Hibernate.orgCommunity Documentation

Hibernate Validator

JSR 349 Reference Implementation

Reference Guide


Preface
1. Getting started
1.1. Project set up
1.1.1. Unified EL
1.1.2. CDI
1.2. Applying constraints
1.3. Validating constraints
1.4. Where to go next?
2. Declaring and validating bean constraints
2.1. Declaring bean constraints
2.1.1. Field-level constraints
2.1.2. Property-level constraints
2.1.3. Class-level constraints
2.1.4. Constraint inheritance
2.1.5. Object graphs
2.2. Validating bean constraints
2.2.1. Obtaining a Validator instance
2.2.2. Validator methods
2.2.3. ConstraintViolation methods
2.3. Built-in constraints
2.3.1. Bean Validation constraints
2.3.2. Additional constraints
3. Declaring and validating method constraints
3.1. Declaring method constraints
3.1.1. Parameter constraints
3.1.2. Return value constraints
3.1.3. Cascaded validation
3.1.4. Method constraints in inheritance hierarchies
3.2. Validating method constraints
3.2.1. Obtaining an ExecutableValidator instance
3.2.2. ExecutableValidator methods
3.2.3. ConstraintViolation methods for method validation
3.3. Built-in method constraints
4. Interpolating constraint error messages
4.1. Default message interpolation
4.1.1. Special characters
4.1.2. Interpolation with message expressions
4.1.3. Examples
4.2. Custom message interpolation
4.2.1. ResourceBundleLocator
5. Grouping constraints
5.1. Requesting groups
5.2. Defining group sequences
5.3. Redefining the default group sequence
5.3.1. @GroupSequence
5.3.2. @GroupSequenceProvider
5.4. Group conversion
6. Creating custom constraints
6.1. Creating a simple constraint
6.1.1. The constraint annotation
6.1.2. The constraint validator
6.1.3. The error message
6.1.4. Using the constraint
6.2. Class-level constraints
6.2.1. Custom property paths
6.3. Cross-parameter constraints
6.4. Constraint composition
7. Configuring via XML
7.1. Configuring the validator factory in validation.xml
7.2. Mapping constraints via constraint-mappings
8. Bootstrapping
8.1. Retrieving ValidatorFactory and Validator
8.1.1. ValidationProviderResolver
8.2. Configuring a ValidatorFactory
8.2.1. MessageInterpolator
8.2.2. TraversableResolver
8.2.3. ConstraintValidatorFactory
8.2.4. ParameterNameProvider
8.2.5. Adding mapping streams
8.2.6. Provider-specific settings
8.3. Configuring a Validator
9. Using constraint metadata
9.1. BeanDescriptor
9.2. PropertyDescriptor
9.3. MethodDescriptor and ConstructorDescriptor
9.4. ElementDescriptor
9.5. GroupConversionDescriptor
9.6. ConstraintDescriptor
10. Integrating with other frameworks
10.1. ORM integration
10.1.1. Database schema-level validation
10.1.2. Hibernate event-based validation
10.1.3. JPA
10.2. JSF & Seam
10.3. CDI
10.3.1. Dependency injection
10.3.2. Method validation
10.4. Java EE
11. Hibernate Validator Specifics
11.1. Public API
11.2. Fail fast mode
11.3. Programmatic constraint declaration
11.4. Boolean composition of constraints
11.5. ResourceBundleLocator
11.6. Custom contexts
11.6.1. HibernateConstraintValidatorContext
11.6.2. HibernateMessageInterpolatorContext
11.7. ParaNamer based ParameterNameProvider
11.8. Unwrapping values prior to validation
12. Annotation Processor
12.1. Prerequisites
12.2. Features
12.3. Options
12.4. Using the Annotation Processor
12.4.1. Command line builds
12.4.2. IDE builds
12.5. Known issues
13. Further reading

This chapter will show you how to get started with Hibernate Validator, the reference implementation (RI) of Bean Validation. For the following quickstart you need:

  • A JDK >= 6

  • Apache Maven

  • An Internet connection (Maven has to download all required libraries)

In order to use Hibernate Validator within a Maven project, simply add the following dependency to your pom.xml:


This transitively pulls in the dependency to the Bean Validation API (javax.validation:validation-api:1.1.0.Final).

Lets dive directly into an example to see how to apply constraints.


The@NotNull, @Size and @Min annotations are used to declare the constraints which should be applied to the fields of a Car instance:

To perform a validation of these constraints, you use a Validator instance. Let's have a look at a unit test forCar:

Example 1.5. Class CarTest showing validation examples

package org.hibernate.validator.referenceguide.chapter01;


                import java.util.Set;
                import javax.validation.ConstraintViolation;
                import javax.validation.Validation;
                import javax.validation.Validator;
                import javax.validation.ValidatorFactory;
                import org.junit.BeforeClass;
                import org.junit.Test;
                import static org.junit.Assert.assertEquals;
                public class CarTest {
                private static Validator validator;
                @BeforeClass
                public static void setUp() {
                ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
                validator = factory.getValidator();
                }
                @Test
                public void manufacturerIsNull() {
                Car car = new Car( null, "DD-AB-123", 4 );
                Set<ConstraintViolation<Car>> constraintViolations =
                validator.validate( car );
                assertEquals( 1, constraintViolations.size() );
                assertEquals( "may not be null", constraintViolations.iterator().next().getMessage() );
                }
                @Test
                public void licensePlateTooShort() {
                Car car = new Car( "Morris", "D", 4 );
                Set<ConstraintViolation<Car>> constraintViolations =
                validator.validate( car );
                assertEquals( 1, constraintViolations.size() );
                assertEquals(
                "size must be between 2 and 14",
                constraintViolations.iterator().next().getMessage()
                );
                }
                @Test
                public void seatCountTooLow() {
                Car car = new Car( "Morris", "DD-AB-123", 1 );
                Set<ConstraintViolation<Car>> constraintViolations =
                validator.validate( car );
                assertEquals( 1, constraintViolations.size() );
                assertEquals(
                "must be greater than or equal to 2",
                constraintViolations.iterator().next().getMessage()
                );
                }
                @Test
                public void carIsValid() {
                Car car = new Car( "Morris", "DD-AB-123", 2 );
                Set<ConstraintViolation<Car>> constraintViolations =
                validator.validate( car );
                assertEquals( 0, constraintViolations.size() );
                }
                }
            

In the setUp() method a Validator object is retrieved from the ValidatorFactory. A Validator instance is thread-safe and may be reused multiple times. It thus can safely be stored in a static field and be used in the test methods to validate the different Car instances.

The validate() method returns a set of ConstraintViolation instances, which you can iterate over in order to see which validation errors occurred. The first three test methods show some expected constraint violations:

  • The @NotNull constraint on manufacturer is violated in manufacturerIsNull()

  • The @Size constraint on licensePlate is violated in licensePlateTooShort()

  • The @Min constraint on seatCount is violated in seatCountTooLow()

If the object validates successfully, validate() returns an empty set as you can see in carIsValid().

Note that only classes from the package javax.validation are used. These are provided from the Bean Validation API. No classes from Hibernate Validator are directly referenced, resulting in portable code.

That concludes the 5 minute tour through the world of Hibernate Validator and Bean Validation. Continue exploring the code examples or look at further examples referenced inChapter 13, Further reading.

To learn more about the validation of beans and properties, just continue readingChapter 2, Declaring and validating bean constraints. If you are interested in using Bean Validation for the validation of method pre- and postcondition refer toChapter 3, Declaring and validating method constraints. In case your application has specific validation requirements have a look at Chapter 6, Creating custom constraints.

In this chapter you will learn how to declare (see Section 2.1, “Declaring bean constraints”) and validate (see Section 2.2, “Validating bean constraints”) bean constraints. Section 2.3, “Built-in constraints” provides an overview of all built-in constraints coming with Hibernate Validator.

If you are interested in applying constraints to method parameters and return values, refer to Chapter 3, Declaring and validating method constraints.

Constraints in Bean Validation are expressed via Java annotations. In this section you will learn how to enhance an object model with these annotations. There are the following three types of bean constraints:

If your model class adheres to the JavaBeans standard, it is also possible to annotate the properties of a bean class instead of its fields. Example 2.2, “Property-level constraints” uses the same entity as in Example 2.1, “Field-level constraints”, however, property level constraints are used.


Note

The property's getter method has to be annotated, not its setter. That way also read-only properties can be constrained which have no setter method.

When using property level constraints property access strategy is used to access the value to be validated, i.e. the validation engine accesses the state via the property accessor method.

Tip

It is recommended to stick either to field or property annotations within one class. It is not recommended to annotate a field and the accompanying getter method as this would cause the field to be validated twice.

The Bean Validation API does not only allow to validate single class instances but also complete object graphs (cascaded validation). To do so, just annotate a field or property representing a reference to another object with @Valid as demonstrated in Example 2.5, “Cascaded validation”.


If an instance of Car is validated, the referenced Person object will be validated as well, as the driver field is annotated with @Valid. Therefore the validation of a Car will fail if the name field of the referenced Person instance is null.

The validation of object graphs is recursive, i.e. if a reference marked for cascaded validation points to an object which itself has properties annotated with @Valid, these references will be followed up by the validation engine as well. The validation engine will ensure that no infinite loops occur during cascaded validation, for example if two objects hold references to each other.

Note that null values are getting ignored during cascaded validation.

Object graph validation also works for collection-typed fields. That means any attributes that

  • are arrays

  • implement java.lang.Iterable (especially Collection, List and Set)

  • implement java.util.Map

can be annotated with @Valid, which will cause each contained element to be validated, when the parent object is validated.


So when validating an instance of the Car class shown in Example 2.6, “Cascaded validation of a collection”, a ConstraintViolation will be created, if any of the Person objects contained in the passengers list has a null name.

The Validator interface is the most important object in Bean Validation. The next section shows how to obtain an Validator instance. Afterwards you'll learn how to use the different methods of the Validator interface.

The Validator interface contains three methods that can be used to either validate entire entities or just single properties of the entity.

All three methods return a Set<ConstraintViolation>. The set is empty, if the validation succeeds. Otherwise a ConstraintViolation instance is added for each violated constraint.

All the validation methods have a var-args parameter which can be used to specify, which validation groups shall be considered when performing the validation. If the parameter is not specified the default validation group (javax.validation.groups.Default) is used. The topic of validation groups is discussed in detail in Chapter 5, Grouping constraints.

Hibernate Validator comprises a basic set of commonly used constraints. These are foremost the constraints defined by the Bean Validation specification (see Table 2.2, “Bean Validation constraints”). Additionally, Hibernate Validator provides useful custom constraints (see Table 2.3, “Custom constraints” and Table 2.4, “Custom country specific constraints”).

Table 2.2, “Bean Validation constraints” shows purpose and supported data types of all constraints specified in the Bean Validation API. All these constraints apply to the field/property level, there are no class-level constraints defined in the Bean Validation specification. If you are using the Hibernate object-relational mapper, some of the constraints are taken into account when creating the DDL for your model (see column "Hibernate metadata impact").

Note

Hibernate Validator allows some constraints to be applied to more data types than required by the Bean Validation specification (e.g. @Max can be applied to Strings). Relying on this feature can impact portability of your application between Bean Validation providers.

Table 2.2. Bean Validation constraints

AnnotationSupported data typesUseHibernate metadata impact
@AssertFalseBoolean, booleanChecks that the annotated element is falseNone
@AssertTrueBoolean, booleanChecks that the annotated element is trueNone
@DecimalMax(value=, inclusive=)BigDecimal, BigInteger, CharSequence, byte, short, int, long and the respective wrappers of the primitive types; Additionally supported by HV: any sub-type of NumberChecks whether the annotated value is less than the specified maximum, when inclusive=false. Otherwise whether the value is less than or equal to the specified maximum. The parameter value is the string representation of the max value according to the BigDecimal string representation.None
@DecimalMin(value=, inclusive=)BigDecimal, BigInteger, CharSequence, byte, short, int, long and the respective wrappers of the primitive types; Additionally supported by HV: any sub-type of NumberChecks whether the annotated value is larger than the specified minimum, when inclusive=false. Otherwise whether the value is larger than or equal to the specified minimum. The parameter value is the string representation of the min value according to the BigDecimal string representation.None
@Digits(integer=, fraction=)BigDecimal, BigInteger, CharSequence, byte, short, int, long and the respective wrappers of the primitive types; Additionally supported by HV: any sub-type of NumberChecks whether the annoted value is a number having up to integer digits and fraction fractional digitsDefines column precision and scale
@Futurejava.util.Date, java.util.Calendar; Additionally supported by HV, if the Joda Time date/time API is on the class path: any implementations of ReadablePartial and ReadableInstantChecks whether the annotated date is in the futureNone
@Max(value=)BigDecimal, BigInteger, byte, short, int, long and the respective wrappers of the primitive types; Additionally supported by HV: any sub-type of CharSequence (the numeric value represented by the character sequence is evaluated), any sub-type of NumberChecks whether the annotated value is less than or equal to the specified maximumAdds a check constraint on the column
@Min(value=)BigDecimal, BigInteger, byte, short, int, long and the respective wrappers of the primitive types; Additionally supported by HV: any sub-type of CharSequence (the numeric value represented by the char sequence is evaluated), any sub-type of NumberChecks whether the annotated value is higher than or equal to the specified minimumAdds a check constraint on the column
@NotNullAny typeChecks that the annotated value is not null.Column(s) are not nullable
@NullAny typeChecks that the annotated value is nullNone
@Pastjava.util.Date, java.util.Calendar; Additionally supported by HV, if the Joda Time date/time API is on the class path: any implementations of ReadablePartial and ReadableInstantChecks whether the annotated date is in the pastNone
@Pattern(regex=, flag=)CharSequenceChecks if the annotated string matches the regular expression regex considering the given flag matchNone
@Size(min=, max=)CharSequence, Collection, Map and arraysChecks if the annotated element's size is between min and max (inclusive)Column length will be set to max
@ValidAny non-primitive typePerforms validation recursively on the associated object. If the object is a collection or an array, the elements are validated recursively. If the object is a map, the value elements are validated recursively.None

Note

On top of the parameters indicated in Table 2.2, “Bean Validation constraints” each constraint has the parameters message, groups and payload. This is a requirement of the Bean Validation specification.

In addition to the constraints defined by the Bean Validation API Hibernate Validator provides several useful custom constraints which are listed in Table 2.3, “Custom constraints”. With one exception also these constraints apply to the field/property level, only @ScriptAssert is a class-level constraint.

Table 2.3. Custom constraints

AnnotationSupported data typesUseHibernate metadata impact
@CreditCardNumberCharSequenceChecks that the annotated character sequence passes the Luhn checksum test. Note, this validation aims to check for user mistakes, not credit card validity! See also Anatomy of Credit Card Numbers.None
@EANCharSequenceChecks that the annotated character sequence is a valid EAN barcode. type determines the type of barcode. The default is EAN-13.None
@EmailCharSequenceChecks whether the specified character sequence is a valid email address. The optional parameters regexp and flags allow to specify an additional regular expression (including regular expression flags) which the email must match.None
@Length(min=, max=)CharSequenceValidates that the annotated character sequence is between min and max includedColumn length will be set to max
@LuhnCheck(startIndex=, endIndex=, checkDigitIndex=, ignoreNonDigitCharacters=)CharSequenceChecks that the digits within the annotated character sequence pass the Luhn checksum algorithm (see also Luhn algorithm). startIndex and endIndex allow to only run the algorithm on the specified sub-string. checkDigitIndex allows to use an arbitrary digit within the character sequence as the check digit. If not specified it is assumed that the check digit is part of the specified range. Last but not least, ignoreNonDigitCharacters allows to ignore non digit characters.None
@Mod10Check(multiplier=, weight=, startIndex=, endIndex=, checkDigitIndex=, ignoreNonDigitCharacters=)CharSequenceChecks that the digits within the annotated character sequence pass the generic mod 10 checksum algorithm. multiplier determines the multiplier for odd numbers (defaults to 3), weight the weight for even numbers (defaults to 1). startIndex and endIndex allow to only run the algorithm on the specified sub-string. checkDigitIndex allows to use an arbitrary digit within the character sequence as the check digit. If not specified it is assumed that the check digit is part of the specified range. Last but not least, ignoreNonDigitCharacters allows to ignore non digit characters.None
@Mod11Check(threshold=, startIndex=, endIndex=, checkDigitIndex=, ignoreNonDigitCharacters=, treatCheck10As=, treatCheck11As=)CharSequenceChecks that the digits within the annotated character sequence pass the mod 11 checksum algorithm. threshold specifies the threshold for the mod11 multiplier growth; if no value is specified the multiplier will grow indefinitely. treatCheck10As and treatCheck11As specify the check digits to be used when the mod 11 checksum equals 10 or 11, respectively. Default to X and 0, respectively. startIndex, endIndex acheckDigitIndex and ignoreNonDigitCharacters carry the same semantics as in @Mod10Check.None
@NotBlankCharSequenceChecks that the annotated character sequence is not null and the trimmed length is greater than 0. The difference to @NotEmpty is that this constraint can only be applied on strings and that trailing whitespaces are ignored.None
@NotEmptyCharSequence, Collection, Map and arraysChecks whether the annotated element is not null nor emptyNone
@Range(min=, max=)BigDecimal, BigInteger, CharSequence, byte, short, int, long and the respective wrappers of the primitive typesChecks whether the annotated value lies between (inclusive) the specified minimum and maximumNone
@SafeHtml(whitelistType=, additionalTags=, additionalTagsWithAttributes=)CharSequence

Checks whether the annotated value contains potentially malicious fragments such as <script/>. In order to use this constraint, the jsoup library must be part of the class path.

With the whitelistType attribute a predefined whitelist type can be chosen which can be refined via additionalTags or additionalTagsWithAttributes. The former allows to add tags without any attributes, whereas the latter allows to specify tags and optionally allowed attributes using the annotation @SafeHtml.Tag.

None
@ScriptAssert(lang=, script=, alias=)Any typeChecks whether the given script can successfully be evaluated against the annotated element. In order to use this constraint, an implementation of the Java Scripting API as defined by JSR 223 ("Scripting for the JavaTM Platform") must part of the class path. The expressions to be evaluated can be written in any scripting or expression language, for which a JSR 223 compatible engine can be found in the class path.None
@URL(protocol=, host=, port= regexp=, flags=)CharSequenceChecks if the annotated character sequence is a valid URL according to RFC2396. If any of the optional parameters protocol, host or port are specified, the corresponding URL fragments must match the specified values. The optional parameters regexp and flags allow to specify an additional regular expression (including regular expression flags) which the URL must match.None

As of Bean Validation 1.1, constraints can not only be applied to JavaBeans and their properties, but also to the parameters and return values of the methods and constructors of any Java type. That way Bean Validation constraints can be used to specify

  • the preconditions that must be satisfied by the caller before a method or constructor may be invoked (by applying constraints to the parameters of an executable)

  • the postconditions that are guaranteed to the caller after a method or constructor invocation returns (by applying constraints to the return value of an executable)

Note

For the purpose of this reference guide, the term method constraint refers to both, method and constructor constraints, if not stated otherwise. Ocassionally, the term executable is used when referering to methods and constructors.

This approach has several advantages over traditional ways of checking the correctness of parameters and return values:

  • the checks don't have to be performed manually (e.g. by throwing IllegalArgumentExceptions or similar), resulting in less code to write and maintain

  • an executable's pre- and postconditions don't have to be expressed again in its documentation, since the constraint annotations will automatically be included in the generated JavaDoc. This avoids redundancies and reduces the chance of inconsistencies between implementation and documentation

Tip

In order to make annotations show up in the JavaDoc of annoted elements, the annotation types themselves must be annotated with the meta annotation @Documented. This is the case for all built-in constraints and is considered a best practice for any custom constraints.

In the remainder of this chapter you will learn how to declare parameter and return value constraints and how to validate them using the ExecutableValidator API.

You specify the preconditions of a method or constructor by adding constraint annotations to its parameters as demonstrated in Example 3.1, “Declaring method and constructor parameter constraints”.


The following preconditions are declared here:

  • The name passed to the RentalCar constructor must not be null

  • When invoking the rentCar() method, the given customer must not be null, the rental's start date must not be null and must be in the future and the rental duration must be at least one day

Note that declaring method or constructor constraints itself does not automatically cause their validation upon invocation of the executable. Instead, the ExecutableValidator API (see Section 3.2, “Validating method constraints”) must be used to perform the validation, which is often done using a method interception facility such as AOP, proxy objects etc.

Constraints may only be applied to instance methods, i.e. declaring constraints on static methods is not supported. Depending on the interception facility you use for triggering method validation, additional restrictions may apply, e.g. with respect to the visibility of methods supported as target of interception. Refer to the documentation of the interception technology to find out whether any such limitations exist.

Sometimes validation does not only depend on a single parameter but on several or even all parameters of a method or constructor. This kind of requirement can be fulfilled with help of a cross-parameter constraint.

Cross-parameter constraints can be considered as the method validation equivalent to class-level constraints. Both can be used to implement validation requirements which are based on several elements. While class-level constraints apply to several properties of a bean, cross-parameter constraints apply to several parameters of an executable.

In contrast to single-parameter constraints, cross-parameter constraints are declared on the method or constructor as you can see in Example 3.2, “Declaring a cross-parameter constraint”. Here the cross-parameter constraint @LuggageCountMatchesPassengerCount declared on the load() method is used to ensure that no passenger has more than two pieces of luggage.


As you will learn in the next section, return value constraints are also declared on the method level. In order to distinguish cross-parameter constraints from return value constraints, the constraint target is configured in the ConstraintValidator implementation using the @SupportedValidationTarget annotation. You can find out about the details in Section 6.3, “Cross-parameter constraints” which shows how to implement your own cross-parameter constraint.

In some cases a constraint can be applied to an executable's parameters (i.e. it is a cross-parameter constraint), but also to the return value. One example for this are custom constraints which allow to specify validation rules using expression or script languages.

Such constraints must define a member validationAppliesTo() which can be used at declaration time to specify the constraint target. As shown in Example 3.3, “Specifying a constraint's target” you apply the constraint to an executable's parameters by specifying validationAppliesTo = ConstraintTarget.PARAMETERS, while ConstraintTarget.RETURN_VALUE is used to apply the constraint to the executable return value.


Although such a constraint is applicable to the parameters and return value of an executable, the target can often be inferred automatically. This is the case, if the constraint is declared on

  • a void method with parameters (the constraint applies to the parameters)

  • an executable with return value but no parameters (the constraint applies to the return value)

  • neither a method nor a constructor, but a field, parameter etc. (the constraint applies to the annotated element)

In these situations you don't have to specify the constraint target. It is still recommended to do so if it increases readability of the source code. If the constraint target is not specified in situations where it can't be determined automatically, a ConstraintDeclarationException is raised.

Similar to the cascaded validation of JavaBeans properties (see Section 2.1.5, “Object graphs”), the @Valid annotation can be used to mark executable parameters and return values for cascaded validation. When validating a parameter or return value annotated with @Valid, the constraints declared on the parameter or return value object are validated as well.

In Example 3.5, “Marking executable parameters and return values for cascaded validation”, the car parameter of the method Garage#checkCar() as well as the return value of the Garage constructor are marked for cascaded validation.


When validating the arguments of the checkCar() method, the constraints on the properties of the passed Car object are evaluated as well. Similarly, the @NotNull constraint on the name field of Garage is checked when validating the return value of the Garage constructor.

Generally, the cascaded validation works for executables in exactly the same way as it does for JavaBeans properties.

In particular, null values are ignored during cascaded validation (naturally this can't happen during constructor return value validation) and cascaded validation is performed recursively, i.e. if a parameter or return value object which is marked for cascaded validation itself has properties marked with @Valid, the constraints declared on the referenced elements will be validated as well.

Cascaded validation can not only be applied to simple object references but also to collection-typed parameters and return values. This means when putting the @Valid annotation to a parameter or return value which

  • is an array

  • implements java.lang.Iterable

  • or implements java.util.Map

each contained element gets validated. So when validating the arguments of the checkCars() method in Example 3.6, “List-typed method parameter marked for cascaded validation”, each element instance of the passed list will be validated and a ConstraintViolation created when any of the contained Car objects is invalid.


When declaring method constraints in inheritance hierarchies, it is important to be aware of the following rules:

These rules are motivated by the concept of behavioral subtyping which requires that wherever a type T is used, also a subtype S of T may be used without altering the program's behavior.

As an example, consider a class invoking a method on an object with the static type T. If the runtime type of that object was S and S imposed additional preconditions, the client class might fail to satisfy these preconditions as is not aware of them. The rules of behavioral subtyping are also known as the Liskov substitution principle.

The Bean Validation specification implements the first rule by disallowing parameter constraints on methods which override or implement a method declared in a supertype (superclass or interface). Example 3.7, “Illegal method parameter constraint in subtype” shows a violation of this rule.


The @Max constraint on Car#drive() is illegal since this method implements the interface method Vehicle#drive(). Note that parameter constraints on overriding methods are also disallowed, if the supertype method itself doesn't declare any parameter constraints.

Furthermore, if a method overrides or implements a method declared in several parallel supertypes (e.g. two interfaces not extending each other or a class and an interface not implemented by that class), no parameter constraints may be specified for the method in any of the involved types. The types in Example 3.8, “Illegal method parameter constraint in parallel types of a hierarchy” demonstrate a violation of that rule. The method RacingCar#drive() overrides Vehicle#drive() as well as Car#drive(). Therefore the constraint on Vehicle#drive() is illegal.


The previously described restrictions only apply to parameter constraints. In contrast, return value constraints may be added in methods overriding or implementing any supertype methods.

In this case, all the method's return value constraints apply for the subtype method, i.e. the constraints declared on the subtype method itself as well as any return value constraints on overridden/implemented supertype methods. This is legal as putting additional return value constraints in place may never represent a weakening of the postconditions guaranteed to the caller of a method.

So when validating the return value of the method Car#getPassengers() shown in Example 3.9, “Return value constraints on supertype and subtype method”, the @Size constraint on the method itself as well as the @NotNull constraint on the implemented interface method Vehicle#getPassengers() apply.


If the validation engine detects a violation of any of the aforementioned rules, a ConstraintDeclarationException will be raised.

Note

The rules described in this section only apply to methods but not constructors. By definition, constructors never override supertype constructors. Therefore, when validating the parameters or the return value of a constructor invocation only the constraints declared on the constructor itself apply, but never any constraints declared on supertype constructors.

The validation of method constraints is done using the ExecutableValidator interface.

In Section 3.2.1, “Obtaining an ExecutableValidator instance” you will learn how to obtain an ExecutableValidator instance while Section 3.2.2, “ExecutableValidator methods” shows how to use the different methods offered by this interface.

Instead of calling the ExecutableValidator methods directly from within application code, they are usually invoked via a method interception technology such as AOP, proxy objects, etc. This causes executable constraints to be validated automatically and transparently upon method or constructor invocation. Typically a ConstraintViolationException is raised by the integration layer in case any of the constraints is violated.

The ExecutableValidator interface offers altogether four methods:

Just as the methods on Validator, all these methods return a Set<ConstraintViolation> which contains a ConstraintViolation instance for each violated constraint and which is empty if the validation succeeds. Also all the methods have a var-args groups parameter by which you can pass the validation groups to be considered for validation.

The examples in the following sections are based on the methods on constructors of the Car class shown in Example 3.11, “Class Car with constrained methods and constructors”.


In addition to the methods introduced in Section 2.2.3, “ConstraintViolation methods”, ConstraintViolation provides two more methods specific to the validation of executable parameters and return values.

ConstraintViolation#getExecutableParameters() returns the validated parameter array in case of method or constructor parameter validation, while ConstraintViolation#getExecutableReturnValue() provides access to the validated object in case of return value validation.

All the other ConstraintViolation methods generally work for method validation in the same way as for validation of beans. Refer to the JavaDoc to learn more about the behavior of the individual methods and their return values during bean and method validation.

Note that getPropertyPath() can be very useful in order to obtain detailed information about the validated parameter or return value, e.g. for logging purposes. In particular, you can retrieve name and argument types of the concerned method as well as the index of the concerned parameter from the path nodes. How this can be done is shown in Example 3.16, “Retrieving method and parameter information”.


The parameter name is determined using the current ParameterNameProvider (see Section 8.2.4, “ParameterNameProvider”) and defaults to arg0, arg1 etc.

In addition to the built-in bean and property-level constraints discussed in Section 2.3, “Built-in constraints”, Hibernate Validator currently provides one method-level constraint, @ParameterScriptAssert. This is a generic cross-parameter constraint which allows to implement validation routines using any JSR 223 compatible ("Scripting for the JavaTM Platform") scripting language, provided an engine for this language is available on the classpath.

To refer to the executable's parameters from within the expression, use their name as obtained from the active parameter name provider (see Section 8.2.4, “ParameterNameProvider”). Example 3.17, “Using @ParameterScriptAssert” shows how the validation logic of the @LuggageCountMatchesPassengerCount constraint from Example 3.2, “Declaring a cross-parameter constraint” could be expressed with the help of @ParameterScriptAssert.


Message interpolation is the process of creating error messages for violated Bean Validation constraints. In this chapter you will learn how such messages are defined and resolved and how you can plug in custom message interpolators in case the default algorithm is not sufficient for your requirements.

Constraint violation messages are retrieved from so called message descriptors. Each constraint defines its default message descriptor using the message attribute. At declaration time, the default descriptor can be overridden with a specific value as shown in Example 4.1, “Specifying a message descriptor using the message attribute”.


If a constraint is violated, its descriptor will be interpolated by the validation engine using the currently configured MessageInterpolator. The interpolated error message can then be retrieved from the resulting constraint violation by calling ConstraintViolation#getMessage().

Message descriptors can contain message parameters as well as message expressions which will be resolved during interpolation. Message parameters are string literals enclosed in {}, while message expressions are string literals enclosed in ${}. The following algorithm is applied during method interpolation:

  1. Resolve any message parameters by using them as key for the resource bundle ValidationMessages. If this bundle contains an entry for a given message parameter, that parameter will be replaced in the message with the corresponding value from the bundle. This step will be executed recursively in case the replaced value again contains message parameters. The resource bundle is expected to be provided by the application developer, e.g. by adding a file named ValidationMessages.properties to the classpath. You can also create localized error messages by providing locale specific variations of this bundle, such as ValidationMessages_en_US.properties. By default, the JVM's default locale (Locale#getDefault()) will be used when looking up messages in the bundle.

  2. Resolve any message parameters by using them as key for a resource bundle containing the standard error messages for the built-in constraints as defined in Appendix B of the Bean Validation specification. In the case of Hibernate Validator, this bundle is named org.hibernate.validator.ValidationMessages. If this step triggers a replacement, step 1 is executed again, otherwise step 3 is applied.

  3. Resolve any message parameters by replacing them with the value of the constraint annotation member of the same name. This allows to refer to attribute values of the constraint (e.g. Size#min()) in the error message (e.g. "must be at least ${min}").

  4. Resolve any message expressions by evaluating them as expressions of the Unified Expression Language. See Section 4.1.2, “Interpolation with message expressions” to learn more about the usage of Unified EL in error messages.

Tip

You can find the formal definition of the interpolation algorithm in section 5.3.1.1 of the Bean Validation specification.

As of Hibernate Validator 5 (Bean Validation 1.1) it is possible to use the Unified Expression Language (as defined by JSR 341) in constraint violation messages. This allows to define error messages based on conditional logic and also enables advanced formatting options. The validation engine makes the following objects available in the EL context:

  • the attribute values of the constraint mapped to the attribute names

  • the currently validated value (property, bean, method parameter etc.) under the name validatedValue

  • a bean mapped to the name formatter exposing the var-arg method format(String format, Object... args) which behaves like java.util.Formatter.format(String format, Object... args).

The following section provides several examples for using EL expressions in error messages.

Example 4.2, “Specifying message descriptors” shows how to make use of the different options for specifying message descriptors.

Example 4.2. Specifying message descriptors

package org.hibernate.validator.referenceguide.chapter04.complete;


public class Car {
    @NotNull
    private String manufacturer;
    @Size(
            min = 2,
            max = 14,
            message = "The license plate '${validatedValue}' must be between {min} and {max} characters long"
    )
    private String licensePlate;
    @Min(
            value = 2,
            message = "There must be at least {value} seat${value > 1 ? 's' : ''}"
    )
    private int seatCount;
    @DecimalMax(
            value = "350",
            message = "The top speed ${formatter.format('%1$.2f', validatedValue)} is higher " +
                    "than {value}"
    )
    private double topSpeed;
    @DecimalMax(value = "100000", message = "Price must not be higher than ${value}")
    private BigDecimal price;
    public Car(
            String manufacturer,
            String licensePlate,
            int seatCount,
            double topSpeed,
            BigDecimal price) {
        this.manufacturer = manufacturer;
        this.licensePlate = licensePlate;
        this.seatCount = seatCount;
        this.topSpeed = topSpeed;
        this.price = price;
    }
    //getters and setters ...
}

Validating an invalid Car instance yields constraint violations with the messages shown by the assertions in Example 4.3, “Expected error messages”:

  • the @NotNull constraint on the manufacturer field causes the error message "may not be null", as this is the default message defined by the Bean Validation specification and no specific descriptor is given in the message attribute

  • the @Size constraint on the licensePlate field shows the interpolation of message parameters ({min}, {max}) and how to add the validated value to the error message using the EL expression ${validatedValue}

  • the @Min constraint on seatCount demonstrates how use an EL expression with a ternery expression to dynamically chose singular or plural form, depending on an attribute of the constraint ("There must be at least 1 seat" vs. "There must be at least 2 seats")

  • the message for the @DecimalMax constraint on topSpeed shows how to format the validated value using the formatter object

  • finally, the @DecimalMax constraint on price shows that parameter interpolation has precedence over expression evaluation, causing the $ sign to show up in front of the maximum price

Tip

Only actual constraint attributes can be interpolated using message parameters in the form {attributeName}. When referring to the validated value or custom expression variables added to the interpolation context (see Section 11.6.1, “HibernateConstraintValidatorContext”), an EL expression in the form ${attributeName} must be used.


If the default message interpolation algorithm does not fit your requirements it is also possible to plug in a custom MessageInterpolator implementation.

Custom interpolators must implement the interface javax.validation.MessageInterpolator. Note that implementations must be thread-safe. It is recommended that custom message interpolators delegate final implementation to the default interpolator, which can be obtained via Configuration#getDefaultMessageInterpolator().

In order to use a custom message interpolator it must be registered either by configuring it in the Bean Validation XML descriptor META-INF/validation.xml (see Section 7.1, “Configuring the validator factory in validation.xml”) or by passing it when bootstrapping a ValidatorFactory or Validator (see Section 8.2.1, “MessageInterpolator” and Section 8.3, “Configuring a Validator”, respectively).

In some use cases you want to use the message interpolation algorithm as defined by the Bean Validation specification, but retrieve error messages from other resource bundles than ValidationMessages. In this situation Hibernate Validator's ResourceBundleLocator SPI can help.

The default message interpolator in Hibernate Validator, ResourceBundleMessageInterpolator, delegates retrieval of resource bundles to that SPI. Using an alternative bundle only requires passing an instance of PlatformResourceBundleLocator with the bundle name when bootstrapping the ValidatorFactory as shown in Example 4.4, “Using a specific resource bundle”.


Of course you also could implement a completely different ResourceBundleLocator, which for instance returns bundles backed by records in a database. In this case you can obtain the default locator via HibernateValidatorConfiguration#getDefaultResourceBundleLocator(), which you e.g. could use as fallback for your custom locator.

Besides PlatformResourceBundleLocator, Hibernate Validator provides another resource bundle locator implementation out of the box, namely AggregateResourceBundleLocator, which allows to retrieve error messages from more than one resource bundle. You could for instance use this implementation in a multi-module application where you want to have one message bundle per module. Example 4.5, “Using AggregateResourceBundleLocator” shows how to use AggregateResourceBundleLocator.


Note that the bundles are processed in the order as passed to the constructor. That means if several bundles contain an entry for a given message key, the value will be taken from the first bundle in the list containing the key.

All validation methods on Validator and ExecutableValidator discussed in earlier chapters also take a var-arg argument groups. So far we have been ignoring this parameter, but it is time to have a closer look.

Groups allow you to restrict the set of constraints applied during validation. One use case for validation groups are UI wizards where in each step only a specified subset of constraints should get validated. The groups targeted are passed as var-arg parameters to the appropriate validate method.

Let's have a look at an example. The class Person in Example 5.1, “Person” has a @NotNull constraint on name. Since no group is specified for this annotation the default group javax.validation.groups.Default is assumed.

Note

When more than one group is requested, the order in which the groups are evaluated is not deterministic. If no group is specified the default group javax.validation.groups.Default is assumed.


The class Driver in Example 5.2, “Driver” extends Person and adds the properties age and hasDrivingLicense. Drivers must be at least 18 years old (@Min(18)) and have a driving license (@AssertTrue). Both constraints defined on these properties belong to the group DriverChecks which is just a simple tagging interface.

Tip

Using interfaces makes the usage of groups type-safe and allows for easy refactoring. It also means that groups can inherit from each other via class inheritance.


Finally the class Car (Example 5.3, “Car”) has some constraints which are part of the default group as well as @AssertTrue in the group CarChecks on the property passedVehicleInspection which indicates whether a car passed the road worthy tests.


Overall three different groups are used in the example:

  • The constraints on Person.name, Car.manufacturer, Car.licensePlate and Car.seatCount all belong to the Default group

  • The constraints on Driver.age and Driver.hasDrivingLicense belong to DriverChecks

  • The constraint on Car.passedVehicleInspection belongs to the group CarChecks

Example 5.4, “Using validation groups” shows how passing different group combinations to the Validator#validate() method results in different validation results.

Example 5.4. Using validation groups

// create a car and check that everything is ok with it.

Car car = new Car( "Morris", "DD-AB-123", 2 );
Set<ConstraintViolation<Car>> constraintViolations = validator.validate( car );
assertEquals( 0, constraintViolations.size() );
// but has it passed the vehicle inspection?
constraintViolations = validator.validate( car, CarChecks.class );
assertEquals( 1, constraintViolations.size() );
assertEquals(
        "The car has to pass the vehicle inspection first",
        constraintViolations.iterator().next().getMessage()
);
// let's go to the vehicle inspection
car.setPassedVehicleInspection( true );
assertEquals( 0, validator.validate( car ).size() );
// now let's add a driver. He is 18, but has not passed the driving test yet
Driver john = new Driver( "John Doe" );
john.setAge( 18 );
car.setDriver( john );
constraintViolations = validator.validate( car, DriverChecks.class );
assertEquals( 1, constraintViolations.size() );
assertEquals(
        "You first have to pass the driving test",
        constraintViolations.iterator().next().getMessage()
);
// ok, John passes the test
john.passedDrivingTest( true );
assertEquals( 0, validator.validate( car, DriverChecks.class ).size() );
// just checking that everything is in order now
assertEquals(
        0, validator.validate(
        car,
        Default.class,
        CarChecks.class,
        DriverChecks.class
).size()
);

The first validate() call in Example 5.4, “Using validation groups” is done using no explicit group. There are no validation errors, even though the property passedVehicleInspection is per default false. However, the constraint defined on this property does not belong to the default group.

The next validation using the CarChecks group fails until the car passes the vehicle inspection. Adding a driver to the car and validating against DriverChecks again yields one constraint violation due to the fact that the driver has not yet passed the driving test. Only after setting passedDrivingTest to true the validation against DriverChecks passes.

The last validate() call finally shows that all constraints are passing by validating against all defined groups.

By default, constraints are evaluated in no particular order, regardless of which groups they belong to. In some situations, however, it is useful to control the order constraints are evaluated.

In the example from Example 5.4, “Using validation groups” it could for instance be required that first all default car constraints are passing before checking the road worthiness of the car. Finally, before driving away, the actual driver constraints should be checked.

In order to implement such a validation order you just need to define an interface and annotate it with @GroupSequence, defining the order in which the groups have to be validated (see Example 5.5, “Defining a group sequence”). If at least one constraint fails in a sequenced group none of the constraints of the following groups in the sequence get validated.


Warning

Groups defining a sequence and groups composing a sequence must not be involved in a cyclic dependency either directly or indirectly, either through cascaded sequence definition or group inheritance. If a group containing such a circularity is evaluated, a GroupDefinitionException is raised.

You then can use the new sequence as shown in in Example 5.6, “Using a group sequence”.


Besides defining group sequences, the @GroupSequence annotation also allows to redefine the default group for a given class. To do so, just add the @GroupSequence annotation to the class and specify the sequence of groups which substitute Default for this class within the annotation.

Example 5.7, “Class RentalCar with redefined default group” introduces a new class RentalCar with a redefined default group.


With this definition you can evaluate the constraints belonging to RentalChecks, CarChecks and RentalCar by just requesting the Default group as seen in Example 5.8, “Validating an object with redefined default group”.


Note

Since there must no cyclic dependency in the group and group sequence definitions one cannot just add Default to the sequence redefining Default for a class. Instead the class itself has to be added!

The Default group sequence overriding is local to the class it is defined on and is not propagated to associated objects. For the example this means that adding DriverChecks to the default group sequence of RentalCar would not have any effects. Only the group Default will be propagated to the driver association.

Note that you can control the propagated group(s) by declaring a group conversion rule (see Section 5.4, “Group conversion”).

In addition to statically redefining default group sequences via @GroupSequence, Hibernate Validator also provides an SPI for the dynamic redefinition of default group sequences depending on the object state.

For that purpose you need to implement the interface DefaultGroupSequenceProvider and register this implementation with the target class via the @GroupSequenceProvider annotation. In the rental car scenario you could for instance dynamically add the CarChecks as seen in Example 5.9, “Implementing and using a default group sequence provider”.


What if you wanted to validate the car related checks together with the driver checks? Of course you could pass the required groups to the validate call explicitly, but what if you wanted to make these validations occur as part of the Default group validation? Here @ConvertGroup comes into play which allows you during cascaded validation to use a different group than the originally requested one.

Let's have a look at Example 5.10, “@ConvertGroup usage”. Here @GroupSequence({ CarChecks.class, Car.class }) is used to combine the car related constraints under the Default group (see Section 5.3, “Redefining the default group sequence”). There is also a @ConvertGroup(from = Default.class, to = DriverChecks.class) which ensures the Default group gets converted to the DriverChecks group during cascaded validation of the driver association.

Example 5.10. @ConvertGroup usage

package org.hibernate.validator.referenceguide.chapter05.groupconversion;


public class Driver {
    @NotNull
    private String name;
    @Min(
            value = 18,
            message = "You have to be 18 to drive a car",
            groups = DriverChecks.class
    )
    public int age;
    @AssertTrue(
            message = "You first have to pass the driving test",
            groups = DriverChecks.class
    )
    public boolean hasDrivingLicense;
    public Driver(String name) {
        this.name = name;
    }
    public void passedDrivingTest(boolean b) {
        hasDrivingLicense = b;
    }
    // getters and setters ...
}
package org.hibernate.validator.referenceguide.chapter05.groupconversion;


@GroupSequence({ CarChecks.class, Car.class })
public class Car {
    @NotNull
    private String manufacturer;
    @NotNull
    @Size(min = 2, max = 14)
    private String licensePlate;
    @Min(2)
    private int seatCount;
    @AssertTrue(
            message = "The car has to pass the vehicle inspection first",
            groups = CarChecks.class
    )
    private boolean passedVehicleInspection;
    @Valid
    @ConvertGroup(from = Default.class, to = DriverChecks.class)
    private Driver driver;
    public Car(String manufacturer, String licencePlate, int seatCount) {
        this.manufacturer = manufacturer;
        this.licensePlate = licencePlate;
        this.seatCount = seatCount;
    }
    // getters and setters ...
}

As a result the validation in Example 5.11, “Test case for @ConvertGroup” succeeds, even though the constraint on hasDrivingLicense belongs to the DriverChecks group and only the Default group is requested in the validate() call.


You can define group conversions wherever @Valid can be used, namely associations as well as method and constructor parameters and return values. Multiple conversions can be specified using @ConvertGroup.List.

However, the following restrictions apply:

  • @ConvertGroup must only be used in combination with @Valid. If used without, a ConstraintDeclarationException is thrown.

  • It is not legal to have multiple conversion rules on the same element with the same from value. In this case, a ConstraintDeclarationException is raised.

  • The from attribute must not refer to a group sequence. A ConstraintDeclarationException is raised in this situation.

Note

Rules are not executed recursively. The first matching conversion rule is used and subsequent rules are ignored. For example if a set of @ConvertGroup declarations chains group A to B and B to C, the group A will be converted to B and not to C.

The Bean Validation API defines a whole set of standard constraint annotations such as @NotNull, @Size etc. In cases where these buit-in constraints are not sufficient, you cean easily create custom constraints tailored to your specific validation requirements.

To create a custom constraint, the following three steps are required:

This section shows how to write a constraint annotation which can be used to ensure that a given string is either completely upper case or lower case. Later on this constraint will be applied to the licensePlate field of the Car class from Chapter 1, Getting started to ensure, that the field is always an upper-case string.

The first thing needed is a way to express the two case modes. While you could use String constants, a better approach is using a Java 5 enum for that purpose:


The next step is to define the actual constraint annotation. If you've never designed an annotation before, this may look a bit scary, but actually it's not that hard:


An annotation type is defined using the @interface keyword. All attributes of an annotation type are declared in a method-like manner. The specification of the Bean Validation API demands, that any constraint annotation defines

  • an attribute message that returns the default key for creating error messages in case the constraint is violated

  • an attribute groups that allows the specification of validation groups, to which this constraint belongs (see Chapter 5, Grouping constraints). This must default to an empty array of type Class<?>.

  • an attribute payload that can be used by clients of the Bean Validation API to assign custom payload objects to a constraint. This attribute is not used by the API itself. An example for a custom payload could be the definition of a severity:

    public class Severity {
    
        public interface Info extends Payload {
        }
        public interface Error extends Payload {
        }
    }
    public class ContactDetails {
        @NotNull(message = "Name is mandatory", payload = Severity.Error.class)
        private String name;
        @NotNull(message = "Phone number not specified, but not mandatory",
                payload = Severity.Info.class)
        private String phoneNumber;
        // ...
    }

    Now a client can after the validation of a ContactDetails instance access the severity of a constraint using ConstraintViolation.getConstraintDescriptor().getPayload() and adjust its behaviour depending on the severity.

Besides these three mandatory attributes there is another one, value, allowing for the required case mode to be specified. The name value is a special one, which can be omitted when using the annotation, if it is the only attribute specified, as e.g. in @CheckCase(CaseMode.UPPER).

In addition, the constraint annotation is decorated with a couple of meta annotations:

  • @Target({ FIELD, METHOD, PARAMETER, ANNOTATION_TYPE }): Defines the supported target element types for the constraint. @CheckCase may be used on fields (element type FIELD), JavaBeans properties as well as method return values (METHOD) and method/constructor parameters (PARAMETER). The element type ANNOTATION_TYPE allows for the creation of composed constraints (see Section 6.4, “Constraint composition”) based on @CheckCase.

    When creating a class-level constraint (see Section 2.1.3, “Class-level constraints”), the element type TYPE would have to be used. Constraints targetting the return value of a constructor need to support the element type CONSTRUCTOR. Cross-parameter constraints (see Section 6.3, “Cross-parameter constraints”) which are used to validate all the parameters of a method or constructor together, must support METHOD or CONSTRUCTOR, respectively.

  • @Retention(RUNTIME): Specifies, that annotations of this type will be available at runtime by the means of reflection

  • @Constraint(validatedBy = CheckCaseValidator.class): Marks the annotation type as constraint annotation and specifies the validator to be used to validate elements annotated with @CheckCase. If a constraint may be used on several data types, several validators may be specified, one for each data type.

  • @Documented: Says, that the use of @CheckCase will be contained in the JavaDoc of elements annotated with it

Finally, there is an inner annotation type named List. This annotation allows to specify several @CheckCase annotations on the same element, e.g. with different validation groups and messages. While also another name could be used, the Bean Validation specification recommends to use the name List and make the annotation an inner annotation of the corresponding constraint type.

Having defined the annotation, you need to create a constraint validator, which is able to validate elements with a @CheckCase annotation. To do so, implement the interface ConstraintValidator as shown below:


The ConstraintValidator interface defines two type parameters which are set in the implementation. The first one specifies the annotation type to be validated (CheckCase), the second one the type of elements, which the validator can handle (String). In case a constraint supports several data types, a ConstraintValidator for each allowed type has to be implemented and registered at the constraint annotation as shown above.

The implementation of the validator is straightforward. The initialize() method gives you access to the attribute values of the validated constraint and allows you to store them in a field of the validator as shown in the example.

The isValid() method contains the actual validation logic. For @CheckCase this is the check whether a given string is either completely lower case or upper case, depending on the case mode retrieved in initialize(). Note that the Bean Validation specification recommends to consider null values as being valid. If null is not a valid value for an element, it should be annotated with @NotNull explicitly.

Example 6.3, “Implementing a constraint validator for the constraint @CheckCase” relies on the default error message generation by just returning true or false from the isValid() method. Using the passed ConstraintValidatorContext object it is possible to either add additional error messages or completely disable the default error message generation and solely define custom error messages. The ConstraintValidatorContext API is modeled as fluent interface and is best demonstrated with an example:


Example 6.4, “Using ConstraintValidatorContext to define custom error messages” shows how you can disable the default error message generation and add a custom error message using a specified message template. In this example the use of the ConstraintValidatorContext results in the same error message as the default error message generation.

Tip

It is important to add each configured constraint violation by calling addConstraintViolation(). Only after that the new constraint violation will be created.

Refer to Section 6.2.1, “Custom property paths” to learn how to use the ConstraintValidatorContext API to control the property path of constraint violations for class-level constraints.

You can now use the constraint in the Car class from the Chapter 1, Getting started chapter to specify that the licensePlate field should only contain upper-case strings:


Finally, Example 6.7, “Validating objects with the @CheckCase constraint” demonstrates how validating a Car object with an invalid license plate causes the @CheckCase constraint to be violated.


As discussed earlier, constraints can also be applied on the class level to validate the state of an entire object. Class-level constraints are defined in the same was as are property constraints. Example 6.8, “Implementing a class-level constraint” shows constraint annotation and validator of the @ValidPassengerCount constraint you already saw in use in Example 2.3, “Class-level constraint”.


As the example demonstrates, you need to use the element type TYPE in the @Target annotation. This allows the constraint to be put on type definitions. The validator of the constraint in the example receives a Car in the isValid() method and can access the complete object state to decide whether the given instance is valid or not.

By default the constraint violation for a class-level constraint is reported on the level of the annotated type, e.g. Car.

In some cases it is preferable though that the violation's property path refers to one of the involved properties. For instance you might want to report the @ValidPassengerCount constraint against the passengers property instead of the Car bean.

Example 6.9, “Adding a new ConstraintViolation with custom property path” shows how this can be done by using the constraint validator context passed to isValid() to build a custom constraint violation with a property node for the property passengers. Note that you also could add several property nodes, pointing to a sub-entity of the validated bean.


Bean Validation distinguishes between two different kinds of constraints.

Generic constraints (which have been discussed so far) apply to the annotated element, e.g. a type, field, method parameter or return value etc. Cross-parameter constraints, in contrast, apply to the array of parameters of a method or constructor and can be used to express validation logic which depends on several parameter values.

In order to define a cross-parameter constraint, its validator class must be annotated with @SupportedValidationTarget(ValidationTarget.PARAMETERS). The type parameter T from the ConstraintValidator interface must resolve to either Object or Object[] in order to receive the array of method/constructor arguments in the isValid() method.

The following example shows the definition of a cross-parameter constraint which can be used to check that two Date parameters of a method are in the correct order:


The definition of a cross-parameter constraint isn't any different from defining a generic constraint, i.e. it must specify the members message(), groups() and payload() and be annotated with @Constraint. This meta annotation also specifies the corresponding validator, which is shown in Example 6.11, “Generic and cross-parameter constraint”. Note that besides the element types METHOD and CONSTRUCTOR also ANNOTATION_TYPE is specified as target of the annotation, in order to enable the creation of composed constraints based on @ConsistentDateParameters (see Section 6.4, “Constraint composition”).

Note

Cross-parameter constraints are specified directly on the declaration of a method or constructor, which is also the case for return value constraints. In order to improve code readability, it is therefore recommended to chose constraint names - such as @ConsistentDateParameters - which make the constraint target apparent.


As discussed above, the validation target PARAMETERS must be configured for a cross-parameter validator by using the @SupportedValidationTarget annotation. Since a cross-parameter constraint could be applied to any method or constructor, it is considered a best practice to check for the expected number and types of parameters in the validator implementation.

As with generic constraints, null parameters should be considered valid and @NotNull on the individual parameters should be used to make sure that parameters are not null.

Tip

Similar to class-level constraints, you can create custom constraint violations on single parameters instead of all parameters when validating a cross-parameter constraint. Just obtain a node builder from the ConstraintValidatorContext passed to isValid() and add a parameter node by calling addParameterNode(). In the example you could use this to create a constraint violation on the end date parameter of the validated method.

In rare situations a constraint is both, generic and cross-parameter. This is the case if a constraint has a validator class which is annotated with @SupportedValidationTarget({ValidationTarget.PARAMETERS, ValidationTarget.ANNOTATED_ELEMENT}) or if it has a generic and a cross-parameter validator class.

When declaring such a constraint on a method which has parameters and also a return value, the intended constraint target can't be determined. Constraints which are generic and cross-parameter at the same time, must therefore define a member validationAppliesTo() which allows the constraint user to specify the constraint's target as shown in Example 6.12, “Generic and cross-parameter constraint”.


The @ScriptAssert constraint has two validators (not shown), a generic and a cross-parameter one and thus defines the member validationAppliesTo(). The default value IMPLICIT allows to derive the target automatically in situations where this is possible (e.g. if the constraint is declared on a field or on a method which has parameters but no return value).

If the target can not be determined implicitly, it must be set by the user to either PARAMETERS or RETURN_VALUE as shown in Example 6.13, “Specifying the target for a generic and cross-parameter constraint”.


Looking at the licensePlate field of the Car class in Example 6.6, “Applying the @CheckCase constraint”, you see three constraint annotations already. In complexer scenarios, where even more constraints could be applied to one element, this might become a bit confusing easily. Furthermore, if there was a licensePlate field in another class, you would have to copy all constraint declarations to the other class as well, violating the DRY principle.

You can address this kind of problem by creating higher level constraints, composed from several basic constraints. Example 6.14, “Creating a composing constraint @ValidLicensePlate” shows a composed constraint annotation which comprises the constraints @NotNull, @Size and @CheckCase:


To create a composed constraint, simply annotate the constraint declaration with its comprising constraints. If the composed constraint itself requires a validator, this validator is to be specified within the @Constraint annotation. For composed constraints which don't need an additional validator such as @ValidLicensePlate, just set validatedBy() to an empty array.

Using the new composed constraint at the licensePlate field is fully equivalent to the previous version, where the three constraints were declared directly at the field itself:


The set of ConstraintViolations retrieved when validating a Car instance will contain an entry for each violated composing constraint of the @ValidLicensePlate constraint. If you rather prefer a single ConstraintViolation in case any of the composing constraints is violated, the @ReportAsSingleViolation meta constraint can be used as follows:


So far we have used the default configuration source for Bean Validation, namely annotations. However, there also exist two kinds of XML descriptors allowing configuration via XML. The first descriptor describes general Bean Validation behaviour and is provided as META-INF/validation.xml. The second one describes constraint declarations and closely matches the constraint declaration approach via annotations. Let's have a look at these two document types.

The key to enable XML configuration for Hibernate Validator is the file META-INF/validation.xml. If this file exists on the classpath its configuration will be applied when the ValidatorFactory gets created. Example 7.1, “validation-configuration-1.1.xsd” shows a model view of the XML schema to which validation.xml has to adhere.


Example 7.2, “validation.xml” shows the several configuration options of validation.xml. All settings are optional and the same configuration options are also available programmatically through javax.validation.Configuration. In fact the XML configuration will be overridden by values explicitly specified via the programmatic API. It is even possible to ignore the XML configuration completely via Configuration#ignoreXmlConfiguration(). See also Section 8.2, “Configuring a ValidatorFactory”.


Warning

There must only be one file named META-INF/validation.xml on the classpath. If more than one is found an exception is thrown.

The node default-provider allows to choose the Bean Validation provider. This is useful if there is more than one provider on the classpath. message-interpolator, traversable-resolver, constraint-validator-factory and parameter-name-provider allow to customize the used implementations for the interfaces MessageInterpolator, TraversableResolver, ConstraintValidatorFactory and ParameterNameProvider defined in the javax.validation package. See the sub-sections of Section 8.2, “Configuring a ValidatorFactory” for more information about these interfaces.

executable-validation and its subnodes define defaults for method validation. The Bean Validation specification defines constructor and non getter methods as defaults. The enabled attribute acts as global switch to turn method validation on and off (see also Chapter 3, Declaring and validating method constraints).

Via the constraint-mapping element you can list an arbitrary number of additional XML files containing the actual constraint configuration. Mapping file names must be specified using their fully-qualified name on the classpath. Details on writing mapping files can be found in the next section.

Last but not least, you can specify provider specific properties via the property nodes. In the example we are using the Hibernate Validator specific hibernate.validator.fail_fast property (see Section 11.2, “Fail fast mode”).

Expressing constraints in XML is possible via files adhering to the schema seen in Example 7.3, “validation-mapping-1.1.xsd”. Note that these mapping files are only processed if listed via constraint-mapping in validation.xml.


Example 7.4, “Bean constraints configured via XML” shows how the classes Car and RentalCar from Example 5.3, “Car” resp. Example 5.7, “Class RentalCar with redefined default group” could be mapped in XML.

Example 7.4. Bean constraints configured via XML


<constraint-mappings
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://jboss.org/xml/ns/javax/validation/mapping validation-mapping-1.1.xsd"
    xmlns="http://jboss.org/xml/ns/javax/validation/mapping" version="1.1">

    <default-package>org.hibernate.validator.referenceguide.chapter05</default-package>
    <bean class="Car" ignore-annotations="true">
        <field name="manufacturer">
            <constraint annotation="javax.validation.constraints.NotNull"/>
        </field>
        <field name="licensePlate">
            <constraint annotation="javax.validation.constraints.NotNull"/>
        </field>
        <field name="seatCount">
            <constraint annotation="javax.validation.constraints.Min">
                <element name="value">2</element>
            </constraint>
        </field>
        <field name="driver">
            <valid/>
        </field>
        <getter name="passedVehicleInspection" ignore-annotations="true">
            <constraint annotation="javax.validation.constraints.AssertTrue">
                <message>The car has to pass the vehicle inspection first</message>
                <groups>
                    <value>CarChecks</value>
                </groups>
                <element name="max">10</element>
            </constraint>
        </getter>
    </bean>
    <bean class="RentalCar" ignore-annotations="true">
        <class ignore-annotations="true">
            <group-sequence>
                <value>RentalCar</value>
                <value>CarChecks</value>
            </group-sequence>
        </class>
    </bean>
    <constraint-definition annotation="org.mycompany.CheckCase">
        <validated-by include-existing-validators="false">
            <value>org.mycompany.CheckCaseValidator</value>
        </validated-by>
    </constraint-definition>
</constraint-mappings>

Example 7.5, “Method constraints configured via XML” shows how the constraints from Example 3.1, “Declaring method and constructor parameter constraints”, Example 3.4, “Declaring method and constructor return value constraints” and Example 3.3, “Specifying a constraint's target” can be expressed in XML.

Example 7.5. Method constraints configured via XML


<constraint-mappings
        xmlns="http://jboss.org/xml/ns/javax/validation/mapping"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation=
                "http://jboss.org/xml/ns/javax/validation/mapping validation-mapping-1.1.xsd" version="1.1">

    <default-package>org.hibernate.validator.referenceguide.chapter07</default-package>

    <bean class="RentalStation" ignore-annotations="true">
        <constructor>
            <return-value>
                <constraint annotation="ValidRentalStation"/>
            </return-value>
        </constructor>

        <constructor>
            <parameter type="java.lang.String">
                <constraint annotation="javax.validation.constraints.NotNull"/>
            </parameter>
        </constructor>

        <method name="getCustomers">
            <return-value>
                <constraint annotation="javax.validation.constraints.NotNull"/>
                <constraint annotation="javax.validation.constraints.Size">
                    <element name="min">1</element>
                </constraint>
            </return-value>
        </method>

        <method name="rentCar">
            <parameter type="Customer">
                <constraint annotation="javax.validation.constraints.NotNull"/>
            </parameter>
            <parameter type="java.util.Date">
                <constraint annotation="javax.validation.constraints.NotNull"/>
                <constraint annotation="javax.validation.constraints.Future"/>
            </parameter>
            <parameter type="int">
                <constraint annotation="javax.validation.constraints.Min">
                    <element name="value">1</element>
                </constraint>
            </parameter>
        </method>
    </bean>

    <bean class="Garage" ignore-annotations="true">
        <method name="buildCar">
            <parameter type="java.util.List"/>
            <cross-parameter>
                <constraint annotation="ELAssert">
                    <element name="expression">...</element>
                    <element name="validationAppliesTo">PARAMETERS</element>
                </constraint>
            </cross-parameter>
        </method>
        <method name="paintCar">
            <parameter type="int"/>
            <return-value>
                <constraint annotation="ELAssert">
                    <element name="expression">...</element>
                    <element name="validationAppliesTo">RETURN_VALUE</element>
                </constraint>
            </return-value>
        </method>
    </bean>

</constraint-mappings>

The XML configuration is closely mirroring the programmatic API. For this reason it should suffice to just add some comments. default-package is used for all fields where a class name is expected. If the specified class is not fully qualified the configured default package will be used. Every mapping file can then have several bean nodes, each describing the constraints on the entity with the specified class name.

Warning

A given entity can only be configured once across all configuration files. The same applies for constraint definitions for a given constraint annotation. It can only occur in one mapping file. If these rules are violated a ValidationException is thrown.

Setting ignore-annotations to true means that constraint annotations placed on the configured bean are ignored. The default for this value is true. ignore-annotations is also available for the nodes class, fields, getter, constructor, method, parameter, cross-parameter and return-value. If not explicitly specified on these levels the configured bean value applies.

The nodes class, field, getter, constructor and method (and its sub node parameter) determine on which level the constraint gets placed. The constraint node is then used to add a constraint on the corresponding level. Each constraint definition must define the class via the annotation attribute. The constraint attributes required by the Bean Validation specification (message, groups and payload) have dedicated nodes. All other constraint specific attributes are configured using the element node.

The class node also allows to reconfigure the default group sequence (see Section 5.3, “Redefining the default group sequence”) via the group-sequence node. Not shown in the example is the use of convert-group to specify group conversions (see Section 5.4, “Group conversion”). This node is available on field, getter, parameter and return-value and specifies a from and to attribute to specify the groups.

Last but not least, the list of ConstraintValidators associated to a given constraint can be altered via the constraint-definition node. The annotation attribute represents the constraint annotation being altered. The validated-by elements represent the (ordered) list of ConstraintValidator implementations associated to the constraint. If include-existing-validator is set to false, validators defined on the constraint annotation are ignored. If set to true, the list of constraint validators described in XML is concatenated to the list of validators specified on the annotation.

In Section 2.2.1, “Obtaining a Validator instance” you already saw one way for creating a Validator instance - via Validation#buildDefaultValidatorFactory(). In this chapter you will learn how to use the other methods in javax.validation.Validation in order to bootstrap specifically configured validators.

You obtain a Validator by retrieving a ValidatorFactory via one of the static methods on javax.validation.Validation and calling getValidator() on the factory instance.

Example 8.1, “Bootstrapping default ValidatorFactory and Validator” shows how to obtain a validator from the default validator factory:


Tip

The generated ValidatorFactory and Validator instances are thread-safe and can be cached. As Hibernate Validator uses the factory as context for caching constraint metadata it is recommended to work with one factory instance within an application.

Bean Validation supports working with several providers such as Hibernate Validator within one application. If more than one provider is present on the classpath, it is not guaranteed which one is chosen when creating a factory via buildDefaultValidatorFactory().

In this case you can explicitly specify the provider to use via Validation#byProvider(), passing the provider's ValidationProvider class as shown in Example 8.2, “Bootstrapping ValidatorFactory and Validator using a specific provider”.


Note that the configuration object returned by configure() allows to specifically customize the factory before calling buildValidatorFactory(). The available options are discussed later in this chapter.

Similarly you can retrieve the default validator factory for configuration which is demonstrated in Example 8.3, “Retrieving the default ValidatorFactory for configuration”.


Note

If a ValidatorFactory instance is no longer in use, it should be disposed by calling ValidatorFactory#close(). This will free any resources possibly allocated by the factory.

By default, available Bean Validation providers are discovered using the Java Service Provider mechanism.

For that purpose, each provider includes the file META-INF/services/javax.validation.spi.ValidationProvider, containing the fully qualified classname of its ValidationProvider implementation. In the case of Hibernate Validator this is org.hibernate.validator.HibernateValidator.

Depending on your environment and its classloading specifics, provider discovery via the Java's service loader mechanism might not work. In this case you can plug in a custom ValidationProviderResolver implementation which performs the provider retrieval. An example is OSGi, where you could implement a provider resolver which uses OSGi services for provider discovery.

To use a custom provider resolver pass it via providerResolver() as shown shown in Example 8.4, “Using a custom ValidationProviderResolver”.


By default validator factories retrieved from Validation and any validators they create are configured as per the XML descriptor META-INF/validation.xml (see Chapter 7, Configuring via XML), if present.

If you want to disable the XML based configuration, you can do so by invoking Configuration#ignoreXmlConfiguration().

The different values of the XML configuration can be accessed via Configuration#getBootstrapConfiguration(). This can for instance be helpful if you want to integrate Bean Validation into a managed environment and want to create managed instances of the objects configured via XML.

Using the fluent configuration API, you can override one or more of the settings when bootstrapping the factory. The following sections show how to make use of the different options. Note that the Configuration class exposes the default implementations of the different extension points which can be useful if you want to use these as delegates for your custom implementations.

In some cases the validation engine should not access the state of a bean property. The most obvious example for that is a lazily loaded property or association of a JPA entity. Validating this lazy property or association would mean that its state would have to be accessed, triggering a load from the database.

Which properties can be accessed and which ones not is controlled by querying the TraversableResolver interface. Example 8.6, “Using a custom TraversableResolver” shows how to use a custom traversable resolver implementation.


Hibernate Validator provides two TraversableResolvers out of the box which will be enabled automatically depending on your environment. The first is DefaultTraversableResolver which will always return true for isReachable() and isTraversable(). The second is JPATraversableResolver which gets enabled when Hibernate Validator is used in combination with JPA 2.

ConstraintValidatorFactory is the extension point for customizing how constraint validators are instantiated and released.

The default ConstraintValidatorFactory provided by Hibernate Validator requires a public no-arg constructor to instantiate ConstraintValidator instances (see Section 6.1.2, “The constraint validator”). Using a custom ConstraintValidatorFactory offers for example the possibility to use dependency injection in constraint validator implementations.

To configure a custom constraint validator factory call Configuration#constraintValidatorFactory() (see Example 8.7, “Using a custom ConstraintValidatorFactory”.


Warning

Any constraint implementations relying on ConstraintValidatorFactory behaviors specific to an implementation (dependency injection, no no-arg constructor and so on) are not considered portable.

Note

ConstraintValidatorFactory implementations should not cache validator instances as the state of each instance can be altered in the initialize() method.

In case a method or constructor parameter constraint is violated, the ParameterNameProvider interface is used to retrieve the parameter's name and make it available to the user via the constraint violation's property path.

The default implementation returns parameter names in the form arg0, arg1 etc., while custom implementations could e.g. be based on parameter annotations, debug symbols or a feature for retrieving parameter names at runtime possibly provided by future Java versions.

Custom ParameterNameProvider implementations are used as demonstrated in Example 8.8, “Using a custom ParameterNameProvider”.


Tip

Hibernate Validator comes with a custom ParameterNameProvider implementation based on the ParaNamer library which provides several ways for obtaining parameter names at runtime. Refer to Section 11.7, “ParaNamer based ParameterNameProvider” to learn more about this specific implementation.

The Bean Validation specification provides not only a validation engine, but also an API for retrieving constraint metadata in a uniform way, no matter whether the constraints are declared using annotations or via XML mappings. Read this chapter to learn more about this API and its possibilities. You can find all the metadata API types in the package javax.validation.metadata.

The examples presented in this chapter are based on the classes and constraint declarations shown in Example 9.1, “Example classes”.

Example 9.1. Example classes

package org.hibernate.validator.referenceguide.chapter07;


public class Person {
    public interface Basic {
    }
    @NotNull
    private String name;
    //getters and setters ...
}
public interface Vehicle {


    public interface Basic {
    }
    @NotNull(groups = Vehicle.Basic.class)
    String getManufacturer();
}
@ValidCar

public class Car implements Vehicle {
    public interface SeverityInfo extends Payload {
    }
    private String manufacturer;
    @NotNull
    @Size(min = 2, max = 14)
    private String licensePlate;
    private Person driver;
    private String modelName;
    public Car() {
    }
    public Car(
            @NotNull String manufacturer,
            String licencePlate,
            Person driver,
            String modelName) {
        this.manufacturer = manufacturer;
        this.licensePlate = licencePlate;
        this.driver = driver;
        this.modelName = modelName;
    }
    public void driveAway(@Max(75) int speed) {
        //...
    }
    @LuggageCountMatchesPassengerCount(
            piecesOfLuggagePerPassenger = 2,
            validationAppliesTo = ConstraintTarget.PARAMETERS,
            payload = SeverityInfo.class,
            message = "There must not be more than {piecesOfLuggagePerPassenger} pieces of " +
                    "luggage per passenger."
    )
    public void load(List<Person> passengers, List<PieceOfLuggage> luggage) {
        //...
    }
    @Override
    @Size(min = 3)
    public String getManufacturer() {
        return manufacturer;
    }
    public void setManufacturer(String manufacturer) {
        this.manufacturer = manufacturer;
    }
    @Valid
    @ConvertGroup(from = Default.class, to = Person.Basic.class)
    public Person getDriver() {
        return driver;
    }
    //further getters and setters...
}

The entry point into the metadata API is the method Validator#getConstraintsForClass(), which returns an instance of the BeanDescriptor interface. Using this descriptor, you can obtain metadata for constraints declared directly on the bean itself (class- or property-level), but also retrieve metadata descriptors representing single properties, methods and constructors.

Example 9.2, “Using BeanDescriptor” demonstrates how to retrieve a BeanDescriptor for the Car class and how to use this descriptor in form of assertions.

Tip

If a constraint declaration hosted by the requested class is invalid, a ValidationException is thrown.

Example 9.2. Using BeanDescriptor

Validator validator = Validation.buildDefaultValidatorFactory().getValidator();


BeanDescriptor carDescriptor = validator.getConstraintsForClass( Car.class );
assertTrue( carDescriptor.isBeanConstrained() );
//one class-level constraint
assertEquals( 1, carDescriptor.getConstraintDescriptors().size() );
//manufacturer, licensePlate, driver
assertEquals( 3, carDescriptor.getConstrainedProperties().size() );
//property has constraint
assertNotNull( carDescriptor.getConstraintsForProperty( "licensePlate" ) );
//property is marked with @Valid
assertNotNull( carDescriptor.getConstraintsForProperty( "driver" ) );
//constraints from getter method in interface and implementation class are returned
assertEquals(
        2,
        carDescriptor.getConstraintsForProperty( "manufacturer" )
                .getConstraintDescriptors()
                .size()
);
//property is not constrained
assertNull( carDescriptor.getConstraintsForProperty( "modelName" ) );
//driveAway(int), load(List<Person>, List<PieceOfLuggage>)
assertEquals( 2, carDescriptor.getConstrainedMethods( MethodType.NON_GETTER ).size() );
//driveAway(int), getManufacturer(), getDriver(), load(List<Person>, List<PieceOfLuggage>)
assertEquals(
        4,
        carDescriptor.getConstrainedMethods( MethodType.NON_GETTER, MethodType.GETTER )
                .size()
);
//driveAway(int)
assertNotNull( carDescriptor.getConstraintsForMethod( "driveAway", int.class ) );
//getManufacturer()
assertNotNull( carDescriptor.getConstraintsForMethod( "getManufacturer" ) );
//setManufacturer() is not constrained
assertNull( carDescriptor.getConstraintsForMethod( "setManufacturer", String.class ) );
//Car(String, String, Person, String)
assertEquals( 1, carDescriptor.getConstrainedConstructors().size() );
//Car(String, String, Person, String)
assertNotNull(
        carDescriptor.getConstraintsForConstructor(
                String.class,
                String.class,
                Person.class,
                String.class
        )
);

You can determine whether the specified class hosts any class- or property-level constraints via isBeanConstrained(). Method or constructor constraints are not considered by isBeanConstrained().

The method getConstraintDescriptors() is common to all descriptors derived from ElementDescriptor (see Section 9.4, “ElementDescriptor”) and returns a set of descriptors representing the constraints directly declared on the given element. In case of BeanDescriptor, the bean's class-level constraints are returned. More details on ConstraintDescriptor can be found in Section 9.6, “ConstraintDescriptor”.

Via getConstraintsForProperty(), getConstraintsForMethod() and getConstraintsForConstructor() you can obtain a descriptor representing one given property or executable element, identified by its name and, in case of methods and constructors, parameter types. The different descriptor types returned by these methods are described in the following sections.

Note that these methods consider constraints declared at super-types according to the rules for constraint inheritance as described in Section 2.1.4, “Constraint inheritance”. An example is the descriptor for the manufacturer property, which provides access to all constraints defined on Vehicle#getManufacturer() and the implementing method Car#getManufacturer(). null is returned in case the specified element does not exist or is not constrained.

The methods getConstrainedProperties(), getConstrainedMethods() and getConstrainedConstructors() return (potentially empty) sets with all constrained properties, methods and constructors, respectively. An element is considered constrained, if it has at least one constraint or is marked for cascaded validation. When invoking getConstrainedMethods(), you can specify the type of the methods to be returned (getters, non-getters or both).

The interface PropertyDescriptor represents one given property of a class. It is transparent whether constraints are declared on a field or a property getter, provided the JavaBeans naming conventions are respected. Example 9.3, “Using PropertyDescriptor” shows how to use the PropertyDescriptor interface.


Using getConstrainedDescriptors(), you can retrieve a set of ConstraintDescriptors providing more information on the individual constraints of a given property. The method isCascaded() returns true, if the property is marked for cascaded validation (either using the @Valid annotation or via XML), false otherwise. Any configured group conversions are returned by getGroupConversions(). See Section 9.5, “GroupConversionDescriptor” for more details on GroupConversionDescriptor.

Constrained methods and constructors are represented by the interfaces MethodDescriptor and ConstructorDescriptor, respectively. Example 9.4, “Using MethodDescriptor and ConstructorDescriptor” demonstrates how to work with these descriptors.

Example 9.4. Using MethodDescriptor and ConstructorDescriptor

//driveAway(int) has a constrained parameter and an unconstrained return value

MethodDescriptor driveAwayDescriptor = carDescriptor.getConstraintsForMethod(
        "driveAway",
        int.class
);
assertEquals( "driveAway", driveAwayDescriptor.getName() );
assertTrue( driveAwayDescriptor.hasConstrainedParameters() );
assertFalse( driveAwayDescriptor.hasConstrainedReturnValue() );
//always returns an empty set; constraints are retrievable by navigating to
//one of the sub-descriptors, e.g. for the return value
assertTrue( driveAwayDescriptor.getConstraintDescriptors().isEmpty() );
ParameterDescriptor speedDescriptor = driveAwayDescriptor.getParameterDescriptors()
        .get( 0 );
//The "speed" parameter is located at index 0, has one constraint and is not cascaded
//nor does it define group conversions
assertEquals( "arg0", speedDescriptor.getName() );
assertEquals( 0, speedDescriptor.getIndex() );
assertEquals( 1, speedDescriptor.getConstraintDescriptors().size() );
assertFalse( speedDescriptor.isCascaded() );
assert speedDescriptor.getGroupConversions().isEmpty();
//getDriver() has no constrained parameters but its return value is marked for cascaded
//validation and declares one group conversion
MethodDescriptor getDriverDescriptor = carDescriptor.getConstraintsForMethod(
        "getDriver"
);
assertFalse( getDriverDescriptor.hasConstrainedParameters() );
assertTrue( getDriverDescriptor.hasConstrainedReturnValue() );
ReturnValueDescriptor returnValueDescriptor = getDriverDescriptor.getReturnValueDescriptor();
assertTrue( returnValueDescriptor.getConstraintDescriptors().isEmpty() );
assertTrue( returnValueDescriptor.isCascaded() );
assertEquals( 1, returnValueDescriptor.getGroupConversions().size() );
//load(List<Person>, List<PieceOfLuggage>) has one cross-parameter constraint
MethodDescriptor loadDescriptor = carDescriptor.getConstraintsForMethod(
        "load",
        List.class,
        List.class
);
assertTrue( loadDescriptor.hasConstrainedParameters() );
assertFalse( loadDescriptor.hasConstrainedReturnValue() );
assertEquals(
        1,
        loadDescriptor.getCrossParameterDescriptor().getConstraintDescriptors().size()
);
//Car(String, String, Person, String) has one constrained parameter
ConstructorDescriptor constructorDescriptor = carDescriptor.getConstraintsForConstructor(
        String.class,
        String.class,
        Person.class,
        String.class
);
assertEquals( "Car", constructorDescriptor.getName() );
assertFalse( constructorDescriptor.hasConstrainedReturnValue() );
assertTrue( constructorDescriptor.hasConstrainedParameters() );
assertEquals(
        1,
        constructorDescriptor.getParameterDescriptors()
                .get( 0 )
                .getConstraintDescriptors()
                .size()
);

getName() returns the name of the given method or constructor. The methods hasConstrainedParameters() and hasConstrainedReturnValue() can be used to perform a quick check whether an executable element has any parameter constraints (either constraints on single parameters or cross-parameter constraints) or return value constraints.

Note that any constraints are not directly exposed on MethodDescriptor and ConstructorDescriptor, but rather on dedicated descriptors representing an executable's parameters, its return value and its cross-parameter constraints. To get hold of one of these descriptors, invoke getParameterDescriptors(), getReturnValueDescriptor() or getCrossParameterDescriptor(), respectively.

These descriptors provide access to the element's constraints (getConstraintDescriptors()) and, in case of parameters and return value, to its configuration for cascaded validation (isValid() and getGroupConversions()). For parameters, you also can retrieve the index and the name, as returned by the currently used parameter name provider (see Section 8.2.4, “ParameterNameProvider”) via getName() and getIndex().

Tip

Getter methods following the JavaBeans naming conventions are considered as bean properties but also as constrained methods.

That means you can retrieve the related metadata either by obtaining a PropertyDescriptor (e.g. BeanDescriptor.getConstraintsForProperty("foo")) or by examining the return value descriptor of the getter's MethodDescriptor (e.g. BeanDescriptor.getConstraintsForMethod("getFoo").getReturnValueDescriptor()).

The ElementDiscriptor interface is the common base class for the individual descriptor types such as BeanDescriptor, PropertyDescriptor etc. Besides getConstraintDescriptors() it provides some more methods common to all descriptors.

hasConstraints() allows for a quick check whether an element has any direct constraints (e.g. class-level constraints in case of BeanDescriptor). getElementClass() returns the Java type of the element represented by a given descriptor. More specifically, the method returns

  • the object type when invoked on BeanDescriptor,

  • the type of a property or parameter when invoked on PropertyDescriptor or ParameterDescriptor respectively,

  • Object[].class when invoked on CrossParameterDescriptor,

  • the return type when invoked on ConstructorDescriptor, MethodDescriptor or ReturnValueDescriptor. void.class will be returned for methods which don't have a return value.

Example 9.5, “Using ElementDescriptor methods” shows how these methods are used.


Finally, ElementDescriptor offers access to the ConstraintFinder API which allows you to query for constraint metadata in a fine grained way. Example 9.6, “Usage of ConstraintFinder” shows how to retrieve a ConstraintFinder instance via findConstraints() and use the API to query for constraint metadata.

Example 9.6. Usage of ConstraintFinder

PropertyDescriptor manufacturerDescriptor = carDescriptor.getConstraintsForProperty(

        "manufacturer"
);
//"manufacturer" constraints are declared on the getter, not the field
assertTrue(
        manufacturerDescriptor.findConstraints()
                .declaredOn( ElementType.FIELD )
                .getConstraintDescriptors()
                .isEmpty()
);
//@NotNull on Vehicle#getManufacturer() is part of another group
assertEquals(
        1,
        manufacturerDescriptor.findConstraints()
                .unorderedAndMatchingGroups( Default.class )
                .getConstraintDescriptors()
                .size()
);
//@Size on Car#getManufacturer()
assertEquals(
        1,
        manufacturerDescriptor.findConstraints()
                .lookingAt( Scope.LOCAL_ELEMENT )
                .getConstraintDescriptors()
                .size()
);
//@Size on Car#getManufacturer() and @NotNull on Vehicle#getManufacturer()
assertEquals(
        2,
        manufacturerDescriptor.findConstraints()
                .lookingAt( Scope.HIERARCHY )
                .getConstraintDescriptors()
                .size()
);
//Combining several filter options
assertEquals(
        1,
        manufacturerDescriptor.findConstraints()
                .declaredOn( ElementType.METHOD )
                .lookingAt( Scope.HIERARCHY )
                .unorderedAndMatchingGroups( Vehicle.Basic.class )
                .getConstraintDescriptors()
                .size()
);

Via declaredOn() you can search for ConstraintDescriptors declared on certain element types. This is useful to find property constraints declared on either fields or getter methods.

unorderedAndMatchingGroups() restricts the resulting constraints to those matching the given validation group(s).

lookingAt() allows to distinguish between constraints directly specified on the element (Scope.LOCAL_ELEMENT) or constraints belonging to the element but hosted anywhere in the class hierarchy (Scope.HIERARCHY).

You can also combine the different options as shown in the last example.

Warning

Order is not respected by unorderedAndMatchingGroups(), but group inheritance and inheritance via sequence are.

Last but not least, the ConstraintDescriptor interface describes a single constraint together with its composing constraints. Via an instance of this interface you get access to the constraint annotation and its parameters.

Example 9.8, “Using ConstraintDescriptor” shows how to retrieve default constraint attributes (such as message template, groups etc.) as well as custom constraint attributes (piecesOfLuggagePerPassenger) and other metadata such as the constraint's annotation type and its validators from a ConstraintDescriptor.

Example 9.8. Using ConstraintDescriptor

//descriptor for the @LuggageCountMatchesPassengerCount constraint on the

//load(List<Person>, List<PieceOfLuggage>) method
ConstraintDescriptor<?> constraintDescriptor = carDescriptor.getConstraintsForMethod(
        "load",
        List.class,
        List.class
).getCrossParameterDescriptor().getConstraintDescriptors().iterator().next();
//constraint type
assertEquals(
        LuggageCountMatchesPassengerCount.class,
        constraintDescriptor.getAnnotation().annotationType()
);
//standard constraint attributes
assertEquals( SeverityInfo.class, constraintDescriptor.getPayload().iterator().next() );
assertEquals(
        ConstraintTarget.PARAMETERS,
        constraintDescriptor.getValidationAppliesTo()
);
assertEquals( Default.class, constraintDescriptor.getGroups().iterator().next() );
assertEquals(
        "There must not be more than {piecesOfLuggagePerPassenger} pieces of luggage per " +
        "passenger.",
        constraintDescriptor.getMessageTemplate()
);
//custom constraint attribute
assertEquals(
        2,
        constraintDescriptor.getAttributes().get( "piecesOfLuggagePerPassenger" )
);
//no composing constraints
assertTrue( constraintDescriptor.getComposingConstraints().isEmpty() );
//validator class
assertEquals(
        Arrays.<Class<?>>asList( LuggageCountMatchesPassengerCount.Validator.class ),
        constraintDescriptor.getConstraintValidatorClasses()
);

Hibernate Validator is intended to be used to implement multi-layered data validation, where constraints are expressed in a single place (the annotated domain model) and checked in various different layers of the application. For this reason there are multiple integration points with other technologies.

Hibernate Validator integrates with both Hibernate and all pure Java Persistence providers.

Hibernate Validator has a built-in Hibernate event listener - org.hibernate.cfg.beanvalidation.BeanValidationEventListener - which is part of Hibernate Annotations (as of Hibernate 3.5.x). Whenever a PreInsertEvent, PreUpdateEvent or PreDeleteEvent occurs, the listener will verify all constraints of the entity instance and throw an exception if any constraint is violated. Per default objects will be checked before any inserts or updates are made by Hibernate. Pre deletion events will per default not trigger a validation. You can configure the groups to be validated per event type using the properties javax.persistence.validation.group.pre-persist, javax.persistence.validation.group.pre-update and javax.persistence.validation.group.pre-remove. The values of these properties are the comma-separated, fully specified class names of the groups to validate. Example 10.1, “Manual configuration of BeanValidationEvenListener” shows the default values for these properties. In this case they could also be omitted.

On constraint violation, the event will raise a runtime ConstraintViolationException which contains a set of ConstraintViolations describing each failure.

If Hibernate Validator is present in the classpath, Hibernate Annotations (or Hibernate EntityManager) will use it transparently. To avoid validation even though Hibernate Validator is in the classpath set javax.persistence.validation.mode to none.

Note

If the beans are not annotated with validation annotations, there is no runtime performance cost.

In case you need to manually set the event listeners for Hibernate Core, use the following configuration in hibernate.cfg.xml:


If you are using JPA 2 and Hibernate Validator is in the classpath the JPA2 specification requires that Bean Validation gets enabled. The properties javax.persistence.validation.group.pre-persist, javax.persistence.validation.group.pre-update and javax.persistence.validation.group.pre-remove as described in Section 10.1.2, “Hibernate event-based validation” can in this case be configured in persistence.xml. persistence.xml also defines a node validation-mode which can be set to AUTO, CALLBACK, NONE. The default is AUTO.

In a JPA 1 you will have to create and register Hibernate Validator yourself. In case you are using Hibernate EntityManager you can add a customized version of the BeanValidationEventListener described in Section 10.1.2, “Hibernate event-based validation” to your project and register it manually.

When working with JSF2 or JBoss Seam™ and Hibernate Validator (Bean Validation) is present in the runtime environment, validation is triggered for every field in the application. Example 10.2, “Usage of Bean Validation within JSF2” shows an example of the f:validateBean tag in a JSF page. The validationGroups attribute is optional and can be used to specify a comma seperated list of validation groups. The default is javax.validation.groups.Default. For more information refer to the Seam documentation or the JSF 2 specification.


Tip

The integration between JSF 2 and Bean Validation is described in the "Bean Validation Integration" chapter of JSR-314. It is interesting to know that JSF 2 implements a custom MessageInterpolator to ensure ensure proper localization. To encourage the use of the Bean Validation message facility, JSF 2 will per default only display the generated Bean Validation message. This can, however, be configured via the application resource bundle by providing the following configuration ({0} is replaced with the Bean Validation message and {1} is replaced with the JSF component label):

javax.faces.validator.BeanValidator.MESSAGE={1}: {0}

The default is:

javax.faces.validator.BeanValidator.MESSAGE={0}

As of version 1.1, Bean Validation is integrated with CDI (Contexts and Dependency Injection for JavaTM EE).

This integration provides CDI managed beans for Validator and ValidatorFactory and enables dependency injection in constraint validators as well as custom message interpolators, traversable resolvers, constraint validator factories and parameter name providers.

Furthermore, parameter and return value constraints on the methods and constructors of CDI managed beans will automatically be validated upon invocation.

When your application runs on a Jave EE container, this integration is enabled by default. When working with CDI in a Servlet container or in a pure Java SE environment, you can use the CDI portable extension provided by Hibernate Validator. To do so, add the portable extension to your class path as described in Section 1.1.2, “CDI”.

CDI's dependency injection mechanism makes it very easy to retrieve ValidatorFactory and Validator instances and use them in your managed beans. Just annotate instance fields of your bean with @javax.inject.Inject as shown in Example 10.3, “Retrieving validator factory and validator via @Inject”.


The injected beans are the default validator factory and validator instances. In order to configure them - e.g. to use a custom message interpolator - you can use the Bean Validation XML descriptors as discussed in Chapter 7, Configuring via XML.

If you are working with several Bean Validation providers you can make sure that factory and validator from Hibernate Validator are injected by annotating the injection points with the @HibernateValidator qualifier which is demonstrated in Example 10.4, “Using the @HibernateValidator qualifier annotation”.


Via @Inject you also can inject dependencies into constraint validators and other Bean Validation objects such as MessageInterpolator implementations etc.

Example 10.5, “Constraint validator with injected bean” demonstrates how an injected CDI bean is used in a ConstraintValidator implementation to determine whether the given constraint is valid or not. As the example shows, you also can work with the @PostConstruct and @PreDestroy callbacks to implement any required construction and destruction logic.


The method interception facilities of CDI allow for a very tight integration with Bean Validation's method validation functionality. Just put constraint annotations to the parameters and return values of the executables of your CDI beans and they will be validated automatically before (parameter constraints) and after (return value constraints) a method or constructor is invoked.

Note that no explicit interceptor binding is required, instead the required method validation interceptor will automatically be registered for all managed beans with constrained methods and constructors.

You can see an example in Example 10.6, “CDI managed beans with method-level constraints”.


Here the RentalStation bean hosts several method constraints. When invoking one of the RentalStation methods from another bean such as RentCarRequest, the constraints of the invoked method are automatically validated. If any illegal parameter values are passed as in the example, a ConstraintViolationException will be thrown by the method interceptor, providing detailed information on the violated constraints. The same is the case if the method's return value violates any return value constraints.

Similarly, constructor constraints are validated automatically upon invocation. In the example the RentalStation object returned by the constructor will be validated since the constructor return value is marked with @Valid.

Bean Validation allows for a fine-grained control of the executable types which are automatically validated. By default, constraints on constructors and non-getter methods are validated. Therefore the @NotNull constraint on the method RentalStation#getAvailableCars() in Example 10.6, “CDI managed beans with method-level constraints” gets not validated when the method is invoked.

You have the following options to configure which types of executables are validated upon invocation:

If several sources of configuration are specified for a given executable, @ValidateOnExecution on the executable level takes precedence over @ValidateOnExecution on the type level and @ValidateOnExecution generally takes precedence over the globally configured types in META-INF/validation.xml.

Example 10.7, “Using @ValidateOnExecution” shows how to use the @ValidateOnExecution annotation:


Here the method rentCar() won't be validated upon invocation because it is annotated with @ValidateOnExecution(type = ExecutableType.NONE). In contrast, the constructor and the method getAvailableCars() will be validated due to @ValidateOnExecution(type = ExecutableType.ALL) being given on the type level. ExecutableType.ALL is a more compact form for explicitly specifying all the types CONSTRUCTORS, GETTER_METHODS and NON_GETTER_METHODS.

Tip

Executable validation can be turned off globally by specifying <executable-validation enabled="false"/> in META-INF/validation.xml. In this case, any @ValidateOnExecution annotations are ignored.

Note that when a method overrides or implements a super-type method the configuration will be taken from that overridden or implemented method (as given via @ValidateOnExecution on the method itself or on the super-type). This protects a client of the super-type method from an unexpected alteration of the configuration, e.g. disabling validation of an overridden executable in a sub-type.

In case a CDI managed bean overrides or implements a super-type method and this super-type method hosts any constraints, it can happen that the validation interceptor is not properly registered with the bean, resulting in the bean's methods not being validated upon invocation. In this case you can specify the executable type IMPLICIT on the sub-class as shown in Example 10.8, “Using ExecutableType.IMPLICIT”, which makes sure that all required metadata is discovered an the validation interceptor kicks in when the methods on ExpressRentalStation are invoked.


In this chapter you will learn how to make use of several features provided by Hibernate Validator in addition to the functionality defined by the Bean Validation specification. This includes the fail fast mode, the API for programmatic constraint configuration and the boolean composition of constraints.

Note

Using the features described in the following sections may result in application code which is not portable between Bean Validation providers.

Let's start, however, with a look at the public API of Hibernate Validator. Table 11.1, “Hibernate Validator public API” lists all packages belonging to this API and describes their purpose. Note that when a package is part of the public this is not necessarily true for its sub-packages.

Table 11.1. Hibernate Validator public API

PackagesDescription
org.hibernate.validatorClasses used by the Bean Validation bootstrap mechanism (eg. validation provider, configuration class); For more details see Chapter 8, Bootstrapping.
org.hibernate.validator.cfg, org.hibernate.validator.cfg.context, org.hibernate.validator.cfg.defsHibernate Validator's fluent API for constraint declaration; In org.hibernate.validator.cfg you will find the ConstraintMapping interface and in org.hibernate.validator.cfg.defs all constraint definitions. Refer to Section 11.3, “Programmatic constraint declaration” for the details.
org.hibernate.validator.constraints, org.hibernate.validator.constraints.brSome useful custom constraints provided by Hibernate Validator in addition to the built-in constraints defined by the Bean Validation specification; The constraints are described in detail in Section 2.3.2, “Additional constraints”.
org.hibernate.validator.constraintvalidationExtended constraint validator context which allows to set custom attributes for message interpolation. Section 11.6.1, “HibernateConstraintValidatorContext” describes how to make use of that feature.
org.hibernate.validator.group, org.hibernate.validator.spi.groupThe group sequence provider feature which allows you to define dynamic default group sequences in function of the validated object state; The specifics can be found in Section 5.3, “Redefining the default group sequence”.
org.hibernate.validator.messageinterpolation, org.hibernate.validator.resourceloading, org.hibernate.validator.spi.resourceloadingClasses related to constraint message interpolation; The first package contains Hibernate Validator's default message interpolator, ResourceBundleMessageInterpolator. The latter two packages provide the ResourceBundleLocator SPI for the loading of resource bundles (see Section 4.2.1, “ResourceBundleLocator”) and its default implementation.
org.hibernate.validator.parameternameproviderA ParameterNameProvider based on the ParaNamer library, see Section 11.7, “ParaNamer based ParameterNameProvider”.
org.hibernate.validator.valuehandling, org.hibernate.validator.spi.valuehandlingClasses related to the processing of values prior to their validation, see Section 11.8, “Unwrapping values prior to validation”.

Note

The public packages of Hibernate Validator fall into two categories: while the actual API parts are intended to be invoked or used by clients (e.g. the API for programmatic constraint declaration or the custom constraints), the SPI (service provider interface) packages contain interfaces which are intended to be implemented by clients (e.g. ResourceBundleLocator).

Any packages not listed in that table are internal packages of Hibernate Validator and are not intended to be accessed by clients. The contents of these internal packages can change from release to release without notice, thus possibly breaking any client code relying on it.

Using the fail fast mode, Hibernate Validator allows to return from the current validation as soon as the first constraint violation occurs. This can be useful for the validation of large object graphs where you are only interested in a quick check whether there is any constraint violation at all.

Example 11.1, “Using the fail fast validation mode” shows how to bootstrap and use a fail fast enabled validator.


Here the validated object actually fails to satisfy both the constraints declared on the Car class, yet the validation call yields only one ConstraintViolation since the fail fast mode is enabled.

Refer to Section 8.2.6, “Provider-specific settings” to learn about the different ways of enabling the fail fast mode when bootstrapping a validator.

As per the Bean Validation specification, you can declare constraints using Java annotations and XML based constraint mappings.

In addition, Hibernate Validator provides a fluent API which allows for the programmatic configuration of constraints. Use cases include the dynamic addition of constraints at runtime depending on some application state or tests where you need entities with different constraints in different scenarios but don't want to implement actual Java classes for each test case.

By default, constraints added via the fluent API are additive to constraints configured via the standard configuration capabilities. But it is also possible to ignore annotation and XML configured constraints where required.

The API is centered around the ConstraintMapping interface. You obtain a new mapping via HibernateValidatorConfiguration#createConstraintMapping() which you then can configure in a fluent manner as shown in Example 11.2, “Programmatic constraint declaration”.


Constraints can be configured on multiple classes and properties using method chaining. The constraint definition classes NotNullDef and SizeDef are helper classes which allow to configure constraint parameters in a type-safe fashion. Definition classes exist for all built-in constraints in the org.hibernate.validator.cfg.defs package. By calling ignoreAnnotations() any constraints configured via annotations or XML are ignored for the given element.

Note

Each element (type, property, method etc.) may only be configured once within all the constraint mappings used to set up one validator factory. Otherwise a ValidationException is raised.

Note

It is not supported to add constraints to non-overridden supertype properties and methods by configuring a subtype. Instead you need to configure the supertype in this case.

Having configured the mapping, you must add it back to the configuration object from which you then can obtain a validator factory.

For custom constraints you can either create your own definition classes extending ConstraintDef or you can use GenericConstraintDef as seen in Example 11.3, “Programmatic declaration of a custom constraint”.


By invoking valid() you can mark a member for cascaded validation which is equivalent to annotating it with @Valid. Configure any group conversions to be applied during cascaded validation using the convertGroup() method (equivalent to @ConvertGroup). An example can be seen in Example 11.4, “Marking a property for cascaded validation”.


You can not only configure bean constraints using the fluent API but also method and constructor constraints. As shown in Example 11.5, “Programmatic declaration of method and constructor constraints” constructors are identified by their parameter types and methods by their name and parameter types. Having selected a method or constructor, you can mark its parameters and/or return value for cascaded validation and add constraints as well as cross-parameter constraints.


Last but not least you can configure the default group sequence or the default group sequence provider of a type as shown in the following example.


Bean Validation specifies that the constraints of a composed constraint (see Section 6.4, “Constraint composition”) are all combined via a logical AND. This means all of the composing constraints need to return true in order for an overall successful validation.

Hibernate Validator offers an extension to this and allows you to compose constraints via a logical OR or NOT. To do so you have to use the ConstraintComposition annotation and the enum CompositionType with its values AND, OR and ALL_FALSE.

Example 11.7, “OR composition of constraints” shows how to build a composed constraint @PatternOrSize where only one of the composing constraints needs to be valid in order to pass the validation. Either the validated string is all lower-cased or it is between two and three characters long.


Tip

Using ALL_FALSE as composition type implicitly enforces that only a single violation will get reported in case validation of the constraint composition fails.

As described in Section 4.2, “Custom message interpolation”, Bean Validation allows to plug in custom message interpolator implementations.

With ResourceBundleLocator, Hibernate Validator provides an additional SPI which allows to retrieve error messages from other resource bundles than ValidationMessages while still using the actual interpolation algorithm as defined by the specification. Refer to Section 4.2.1, “ResourceBundleLocator” to learn how to make use of that SPI.

The Bean Validation specification offers at several points in its API the possibility to unwrap a given interface to a implementor specific subtype. In the case of constraint violation creation in ConstraintValidator implementations as well as message interpolation in Messageinterpolator instances, there exist unwrap() methods for the provided context instances - ConstraintValidatorContext respectively MessageInterpolatorContext. Hibernate Validator provides custom extensions for both of these interfaces.

HibernateConstraintValidatorContext is a subtype of ConstraintValidatorContext which allows you to set arbitrary parameters for interpolation via the Expression Language message interpolation facility (see Section 4.1.2, “Interpolation with message expressions”). For example the default error message for the @Future constraint is "must be in the future". What if you would like to include the current date to make the message more explicit? Example 11.8, “Custom @Future validator with message parameters” shows how this could be achieved.


Note

Note that the parameters specified via addExpressionVariable(String, Object) are global and apply for all constraint violations created by this isValid() invocation. This includes the default constraint violation, but also all violations created by the ConstraintViolationBuilder. You can, however, update the parameters between invocations of ConstraintViolationBuilder#addConstraintViolation().

Warning

This functionality is currently experimental and might change in future versions.

Hibernate Validator comes with a ParameterNameProvider implementation which leverages the ParaNamer library.

This library provides several ways for obtaining parameter names at runtime, e.g. based on debug symbols created by the Java compiler, constants with the parameter names woven into the bytecode in a post-compile step or annotations such as the @Named annotation from JSR 330.

In order to use ParanamerParameterNameProvider, either pass an instance when bootstrapping a validator as shown in Example 8.8, “Using a custom ParameterNameProvider” or specify org.hibernate.validator.parameternameprovider.ParanamerParameterNameProvider as value for the <parameter-name-provider> element in the META-INF/validation.xml file.

Tip

When using this parameter name provider, you need to add the ParaNamer library to your classpath. It is available in the Maven Central repository with the group id com.thoughtworks.paranamer and the artifact id paranamer.

By default ParanamerParameterNameProvider retrieves parameter names from constants added to the byte code at build time (via DefaultParanamer) and debug symbols (via BytecodeReadingParanamer). Alternatively you can specify a Paranamer implementation of your choice when creating a ParanamerParameterNameProvider instance.

Sometimes it is required to unwrap values prior to the validation. E.g. in Example 11.10, “Using@UnwrapValidatedValue” property types as specified by JavaFX are used to define an element of some domain model.


Note

The concept of value unwrapping is considered experimental at this time and may evolve into more general means of value handling in future releases. Please let us know about your use cases for such functionality.

In JavaFX, bean properties are typically not of simple data types like String or int, but are wrapped in Property types which allows to make them observable, use them for data binding etc. When applying a constraint such as @Size to an element of type Property<String> without further preparation, an exception would be raised, indicating that no suitable validator for that constraint and data type can be found. Thus the validated value must be unwrapped from the containing property object before looking up a validator and invoking it.

To do so, put the @UnwrapValidatedValue annotation to the element in question. This will advice the validation engine to look for an unwrapper implementation which returns the data type to be used for constraint validator resolution and unwraps the validated value. Unwrapper types must extend the SPI class ValidatedValueUnwrapper as shown in Example 11.11, “Implementing the ValidatedValueUnwrapper interface”.


Value unwrappers must be registered when obtaining a Validator instance as follows:


Several unwrapper implementations can be registered when working with different kinds of wrapper types in one application. Note that it is not specified which of the unwrapper implementations is chosen when more than one implementation is suitable to unwrap a given element.

Alternatively, the fully-qualified names of one ore more unwrapper implementations can be specified via the configuration property hibernate.validator.validated_value_handlers which can be useful when configuring the default validator factory using the descriptor META-INF/validation.xml (see Chapter 7, Configuring via XML).

Have you ever caught yourself by unintentionally doing things like

  • specifying constraint annotations at unsupported data types (e.g. by annotating a String with @Past)

  • annotating the setter of a JavaBeans property (instead of the getter method)

  • annotating static fields/methods with constraint annotations (which is not supported)?

Then the Hibernate Validator Annotation Processor is the right thing for you. It helps preventing such mistakes by plugging into the build process and raising compilation errors whenever constraint annotations are incorrectly used.

Tip

You can find the Hibernate Validator Annotation Processor as part of the distribution bundle on Sourceforge or in the usual Maven repositories such as Maven Central under the GAV org.hibernate:hibernate-validator-annotation-processor:5.1.0.Final.

This section shows in detail how to integrate the Hibernate Validator Annotation Processor into command line builds (javac, Ant, Maven) as well as IDE-based builds (Eclipse, IntelliJ IDEA, NetBeans).

When compiling on the command line using javac, specify the JAR hibernate-validator-annotation-processor-5.1.0.Final.jar using the "processorpath" option as shown in the following listing. The processor will be detected automatically by the compiler and invoked during compilation.


There are several options for integrating the annotation processor with Apache Maven. Generally it is sufficient to add the Hibernate Validator Annotation Processor as dependency to your project:


The processor will then be executed automatically by the compiler. This basically works, but comes with the disadavantage that in some cases messages from the annotation processor are not displayed (see MCOMPILER-66).

Another option is using the Maven Annotation Plugin. To work with this plugin, disable the standard annotation processing performed by the compiler plugin and configure the annotation plugin by specifying an execution and adding the Hibernate Validator Annotation Processor as plugin dependency (that way the processor is not visible on the project's actual classpath):


Do the following to use the annotation processor within the Eclipse IDE:

  • Right-click your project, choose "Properties"

  • Go to "Java Compiler" and make sure, that "Compiler compliance level" is set to "1.6". Otherwise the processor won't be activated

  • Go to "Java Compiler - Annotation Processing" and choose "Enable annotation processing"

  • Go to "Java Compiler - Annotation Processing - Factory Path" and add the JAR hibernate-validator-annotation-processor-5.1.0.Final.jar

  • Confirm the workspace rebuild

You now should see any annotation problems as regular error markers within the editor and in the "Problem" view:

The following steps must be followed to use the annotation processor within IntelliJ IDEA (version 9 and above):

  • Go to "File", then "Settings",

  • Expand the node "Compiler", then "Annotation Processors"

  • Choose "Enable annotation processing" and enter the following as "Processor path": /path/to/hibernate-validator-annotation-processor-5.1.0.Final.jar

  • Add the processor's fully qualified name org.hibernate.validator.ap.ConstraintValidationProcessor to the "Annotation Processors" list

  • If applicable add you module to the "Processed Modules" list

Rebuilding your project then should show any erronous constraint annotations:

Starting with version 6.9, also the NetBeans IDE supports using annotation processors within the IDE build. To do so, do the following:

  • Right-click your project, choose "Properties"

  • Go to "Libraries", tab "Processor", and add the JAR hibernate-validator-annotation-processor-5.1.0.Final.jar

  • Go to "Build - Compiling", select "Enable Annotation Processing" and "Enable Annotation Processing in Editor". Add the annotation processor by specifying its fully qualified name org.hibernate.validator.ap.ConstraintValidationProcessor

Any constraint annotation problems will then be marked directly within the editor:

The following known issues exist as of May 2010:

  • HV-308: Additional validators registered for a constraint using XML are not evaluated by the annotation processor.

  • Sometimes custom constraints can't be properly evaluated when using the processor within Eclipse. Cleaning the project can help in these situations. This seems to be an issue with the Eclipse JSR 269 API implementation, but further investigation is required here.

  • When using the processor within Eclipse, the check of dynamic default group sequence definitions doesn't work. After further investigation, it seems to be an issue with the Eclipse JSR 269 API implementation.

Last but not least, a few pointers to further information.

A great source for examples is the Bean Validation TCK which is available for anonymous access on GitHub. In particular the TCK's tests might be of interest. The JSR 349 specification itself is also a great way to deepen your understanding of Bean Validation resp. Hibernate Validator.

If you have any further questions to Hibernate Validator or want to share some of your use cases have a look at the Hibernate Validator Wiki and the Hibernate Validator Forum.

In case you would like to report a bug use Hibernate's Jira instance. Feedback is always welcome!