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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:
Not all constraints can be placed on all of these levels. In fact, none of the default constraints
defined by Bean Validation can be placed at class level. The java.lang.annotation.Target annotation
in the constraint annotation itself determines on which elements a constraint can be placed. See
Chapter 6, Creating custom constraints for more information.
Constraints can be expressed by annotating a field of a class. Example 2.1, “Field-level constraints” shows a field level configuration example:
Example 2.1. Field-level constraints
package org.hibernate.validator.referenceguide.chapter02.fieldlevel;
public class Car {
@NotNull
private String manufacturer;
@AssertTrue
private boolean isRegistered;
public Car(String manufacturer, boolean isRegistered) {
this.manufacturer = manufacturer;
this.isRegistered = isRegistered;
}
//getters and setters...
}When using field-level constraints field access strategy is used to access the value to be validated. This means the validation engine directly accesses the instance variable and does not invoke the property accessor method even if such an accessor exists.
Constraints can be applied to fields of any access type (public, private etc.). Constraints on static fields are not supported, though.
When validating byte code enhanced objects property level constraints should be used, because the byte code enhancing library won’t be able to determine a field access via reflection.
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.
Example 2.2. Property-level constraints
package org.hibernate.validator.referenceguide.chapter02.propertylevel;
public class Car {
private String manufacturer;
private boolean isRegistered;
public Car(String manufacturer, boolean isRegistered) {
this.manufacturer = manufacturer;
this.isRegistered = isRegistered;
}
@NotNull
public String getManufacturer() {
return manufacturer;
}
public void setManufacturer(String manufacturer) {
this.manufacturer = manufacturer;
}
@AssertTrue
public boolean isRegistered() {
return isRegistered;
}
public void setRegistered(boolean isRegistered) {
this.isRegistered = isRegistered;
}
}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.
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.
Starting from Java 8, it is possible to specify constraints directly on the type argument of a
parameterized type. However, this requires that ElementType.TYPE_USE is specified via @Target
in the constraint definition. To maintain backwards compatibility, built-in Bean Validation as well as
Hibernate Validator specific constraints do not yet specify ElementType.TYPE_USE. To make use of
type argument constraints, custom constraints must be used (see Chapter 6, Creating custom constraints).
Hibernate Validator validates type arguments constraints specified on collections, map values,
java.util.Optional, and custom parameterized types.
When applying constraints on an Iterable type argument, Hibernate Validator will validate each
element. Example 2.3, “Type argument constraint on List” shows an example of a
List with a type argument constraint.
Example 2.3. Type argument constraint on List
package org.hibernate.validator.referenceguide.chapter02.typeargument;
public class Car {
@Valid
private List<@ValidPart String> parts = new ArrayList<>();
public void addPart(String part) {
parts.add( part );
}
//...
}Car car = Car();
car.addPart( "Wheel" );
car.addPart( null );
Set<ConstraintViolation<Car>> constraintViolations = validator.validate( car );
assertEquals( 1, constraintViolations.size() );
assertEquals(
"'null' is not a valid car part.",
constraintViolations.iterator().next().getMessage()
);
assertEquals( "parts[1]", constraintViolations.iterator().next().getPropertyPath().toString() );Type argument constraints are also validated for map values. Constraints on the key are ignored.
Example 2.4, “Type argument constraint on maps” shows an example of a Map value with a type
argument constraint.
Example 2.4. Type argument constraint on maps
package org.hibernate.validator.referenceguide.chapter02.typeargument;
public class Car {
public static enum FuelConsumption {
CITY,
HIGHWAY
}
@Valid
private EnumMap<FuelConsumption, @MaxAllowedFuelConsumption Integer> fuelConsumption = new EnumMap<>( FuelConsumption.class );
public void setFuelConsumption(FuelConsumption consumption, int value) {
fuelConsumption.put( consumption, value );
}
//...
}Car car = new Car();
car.setFuelConsumption( Car.FuelConsumption.HIGHWAY, 20 );
Set<ConstraintViolation<Car>> constraintViolations = validator.validate( car );
assertEquals( 1, constraintViolations.size() );
assertEquals( "20 is outside the max fuel consumption.", constraintViolations.iterator().next().getMessage() );When applying a constraint on the type argument of Optional, Hibernate Validator will automatically
unwrap the type and validate the internal value. Example 2.5, “Type argument constraint on Optional” shows
an example of an Optional with a type argument constraint.
Example 2.5. Type argument constraint on Optional
package org.hibernate.validator.referenceguide.chapter02.typeargument;
import java.util.ArrayList;
import java.util.EnumMap;
import java.util.List;
import java.util.Optional;
import javax.validation.Valid;
public class Car {
private Optional<@MinTowingCapacity(1000) Integer> towingCapacity = Optional.empty();
public void setTowingCapacity(Integer alias) {
towingCapacity = Optional.of( alias );
}
//...
}Car car = Car();
car.setTowingCapacity( 100 );
Set<ConstraintViolation<Car>> constraintViolations = validator.validate( car );
assertEquals( 1, constraintViolations.size() );
assertEquals( "Not enough towing capacity.", constraintViolations.iterator().next().getMessage() );
assertEquals( "towingCapacity", constraintViolations.iterator().next().getPropertyPath().toString() );Type arguments constraints can with two restrictions also be used with custom types. First, a
ValidatedValueUnwrapper must be registered for the custom type allowing to retrieve
the value to validate (see Section 11.11, “Unwrapping values”). Second, only types with one type arguments
are supported. Parameterized types with two or more type arguments are not checked for type argument
constraints. This limitation might change in future versions.
Example 2.6, “Type argument constraint on custom parameterized type” shows an example of a custom parameterized type with a type argument constraint.
Example 2.6. Type argument constraint on custom parameterized type
package org.hibernate.validator.referenceguide.chapter02.typeargument;
public class Car {
private GearBox<@MinTorque(100) Gear> gearBox;
public void setGearBox(GearBox<Gear> gearBox) {
this.gearBox = gearBox;
}
//...
}package org.hibernate.validator.referenceguide.chapter02.typeargument;
public class GearBox<T extends Gear> {
private final T gear;
public GearBox(T gear) {
this.gear = gear;
}
public Gear getGear() {
return this.gear;
}
}package org.hibernate.validator.referenceguide.chapter02.typeargument;
public class Gear {
private final Integer torque;
public Gear(Integer torque) {
this.torque = torque;
}
public Integer getTorque() {
return torque;
}
public static class AcmeGear extends Gear {
public AcmeGear() {
super( 100 );
}
}
}package org.hibernate.validator.referenceguide.chapter02.typeargument;
public class GearBoxUnwrapper extends ValidatedValueUnwrapper<GearBox> {
@Override
public Object handleValidatedValue(GearBox gearBox) {
return gearBox == null ? null : gearBox.getGear();
}
@Override
public Type getValidatedValueType(Type valueType) {
return Gear.class;
}
}Car car = Car();
car.setGearBox( new GearBox<>( new Gear.AcmeGear() ) );
Set<ConstraintViolation<Car>> constraintViolations = validator.validate( car );
assertEquals( 1, constraintViolations.size() );
assertEquals( "Gear is not providing enough torque.", constraintViolations.iterator().next().getMessage() );
assertEquals( "gearBox", constraintViolations.iterator().next().getPropertyPath().toString() );Last but not least, a constraint can also be placed on the class level. In this case not a single property is subject of the validation but the complete object. Class-level constraints are useful if the validation depends on a correlation between several properties of an object.
The Car class in Example 2.7, “Class-level constraint” has the two attributes seatCount and passengers and it
should be ensured that the list of passengers has not more entries than seats are available. For
that purpose the @ValidPassengerCount constraint is added on the class level. The validator of that
constraint has access to the complete Car object, allowing to compare the numbers of seats and
passengers.
Refer to Section 6.2, “Class-level constraints” to learn in detail how to implement this custom constraint.
Example 2.7. Class-level constraint
package org.hibernate.validator.referenceguide.chapter02.classlevel;
@ValidPassengerCount
public class Car {
private int seatCount;
private List<Person> passengers;
//...
}When a class implements an interface or extends another class, all constraint annotations declared on the super-type apply in the same manner as the constraints specified on the class itself. To make things clearer let’s have a look at the following example:
Example 2.8. Constraint inheritance
package org.hibernate.validator.referenceguide.chapter02.inheritance;
public class Car {
private String manufacturer;
@NotNull
public String getManufacturer() {
return manufacturer;
}
//...
}package org.hibernate.validator.referenceguide.chapter02.inheritance;
public class RentalCar extends Car {
private String rentalStation;
@NotNull
public String getRentalStation() {
return rentalStation;
}
//...
}Here the class RentalCar is a subclass of Car and adds the property rentalStation. If an instance of
RentalCar is validated, not only the @NotNull constraint on rentalStation is evaluated, but also the
constraint on manufacturer from the parent class.
The same would be true, if Car was not a superclass but an interface implemented by RentalCar.
Constraint annotations are aggregated if methods are overridden. So if RentalCar overrode the
getManufacturer() method from Car, any constraints annotated at the overriding method would be
evaluated in addition to the @NotNull constraint from the superclass.
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 2.9, “Cascaded validation”.
Example 2.9. Cascaded validation
package org.hibernate.validator.referenceguide.chapter02.objectgraph;
public class Car {
@NotNull
@Valid
private Person driver;
//...
}package org.hibernate.validator.referenceguide.chapter02.objectgraph;
public class Person {
@NotNull
private String name;
//...
}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
java.lang.Iterable (especially Collection, List and Set)java.util.Mapcan be annotated with @Valid, which will cause each contained element to be validated, when the
parent object is validated.
Example 2.10. Cascaded validation of a collection
package org.hibernate.validator.referenceguide.chapter02.objectgraph.list;
public class Car {
@NotNull
@Valid
private List<Person> passengers = new ArrayList<Person>();
//...
}So when validating an instance of the Car class shown in Example 2.10, “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 first step towards validating an entity instance is to get hold of a Validator instance. The
road to this instance leads via the Validation class and a ValidatorFactory. The easiest way is to
use the static method Validation#buildDefaultValidatorFactory():
Example 2.11. Validation#buildDefaultValidatorFactory()
ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
Validator validator = factory.getValidator();This bootstraps a validator in the default configuration. Refer to Chapter 8, Bootstrapping to
learn more about the different bootstrapping methods and how to obtain a specifically configured
Validator instance.
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.
Use the validate() method to perform validation of all constraints of a given bean.
Example 2.12, “Using Validator#validate()” shows the validation of an instance of the Car class from
Example 2.2, “Property-level constraints” which fails to satisfy the @NotNull constraint on the manufacturer
property. The validation call therefore returns one ConstraintViolation object.
Example 2.12. Using Validator#validate()
Car car = new Car( null, true );
Set<ConstraintViolation<Car>> constraintViolations = validator.validate( car );
assertEquals( 1, constraintViolations.size() );
assertEquals( "may not be null", constraintViolations.iterator().next().getMessage() );With help of the validateProperty() you can validate a single named property of a given object. The
property name is the JavaBeans property name.
Example 2.13. Using Validator#validateProperty()
Car car = new Car( null, true );
Set<ConstraintViolation<Car>> constraintViolations = validator.validateProperty(
car,
"manufacturer"
);
assertEquals( 1, constraintViolations.size() );
assertEquals( "may not be null", constraintViolations.iterator().next().getMessage() );By using the validateValue() method you can check whether a single property of a given class can be
validated successfully, if the property had the specified value:
Example 2.14. Using Validator#validateValue()
Set<ConstraintViolation<Car>> constraintViolations = validator.validateValue(
Car.class,
"manufacturer",
null
);
assertEquals( 1, constraintViolations.size() );
assertEquals( "may not be null", constraintViolations.iterator().next().getMessage() );
---@Valid is not honored by validateProperty() or validateValue().
Validator#validateProperty() is for example used in the integration of Bean Validation into JSF 2
(see Section 10.2, “JSF & Seam”) to perform a validation of the values entered into a form
before they are propagated to the model.
Now it is time to have a closer look at what a ConstraintViolation is. Using the different methods
of ConstraintViolation a lot of useful information about the cause of the validation failure can be
determined. Table 2.1, “The various ConstraintViolation methods” gives an overview of these methods. The values in the
"Example" column refer to Example 2.12, “Using Validator#validate()”.
Table 2.1. The various ConstraintViolation methods
| Method | Usage | Example |
|---|---|---|
| The interpolated error message | "may not be null" |
| The non-interpolated error message | "{… NotNull.message}" |
| The root bean being validated | car |
| The class of the root bean being validated |
|
| If a bean constraint, the bean instance the constraint is applied on; If a property constraint, the bean instance hosting the property the constraint is applied on |
|
| The property path to the validated value from root bean | contains one node with kind
|
| The value failing to pass the constraint |
|
| Constraint metadata reported to fail | descriptor for |
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").
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
| Annotation | Supported data types | Use | Hibernate metadata impact |
|---|---|---|---|
|
| Checks that the annotated element is false | None |
|
| Checks that the annotated element is true | None |
|
| Checks 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
| None |
|
| Checks 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
| None |
| BigDecimal,
| Checks whether the annotated value is a number having up to
| Defines column precision and scale |
|
| Checks whether the annotated date is in the future | None |
|
| Checks whether the annotated value is less than or equal to the specified maximum | Adds a check constraint on the column |
|
| Checks whether the annotated value is higher than or equal to the specified minimum | Adds a check constraint on the column |
| Any type | Checks that the annotated value is not
| Column(s) are not nullable |
| Any type | Checks that the annotated value is
| None |
|
| Checks whether the annotated date is in the past | None |
|
| Checks if the annotated string matches the regular
expression | None |
|
| Checks if the annotated element’s size is between | Column length will be set to
|
| Any non-primitive type | Performs 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 |
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
| Annotation | Supported data types | Use | Hibernate metadata impact |
|---|---|---|---|
|
| Checks 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 |
|
| Checks that the annotated character sequence is a valid EAN barcode. type determines the type of barcode. The default is EAN-13. | None |
|
| Checks whether the specified character sequence is a valid email address. The optional parameters
| None |
|
| Validates that the annotated character sequence is
between | Column length will be set to max |
|
| Checks that the digits within the annotated character
sequence pass the Luhn checksum algorithm (see also
Luhn algorithm). | None |
|
| Checks that the digits within the annotated character
sequence pass the generic mod 10 checksum algorithm.
| None |
|
| Checks that the digits within the annotated character
sequence pass the mod 11 checksum algorithm.
| None |
|
| Checks that the annotated character sequence is not null
and the trimmed length is greater than 0. The difference to
| None |
|
| Checks whether the annotated element is not null nor empty | None |
|
| Checks whether the annotated value lies between (inclusive) the specified minimum and maximum | None |
|
| Checks whether the annotated value
contains potentially malicious fragments such as | None |
| Any type | Checks 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 |
|
| Checks if the annotated character sequence is a valid URL
according to RFC2396. If any of the optional parameters
| None |
Hibernate Validator offers also some country specific constraints, e.g. for the validation of social security numbers.
If you have to implement a country specific constraint, consider making it a contribution to Hibernate Validator!
Table 2.4. Custom country specific constraints
| Annotation | Supported data types | Use | Country | Hibernate metadata impact |
|---|---|---|---|---|
|
| Checks that the annotated character sequence represents a Brazilian corporate tax payer registry number (Cadastro de Pessoa Juríeddica) | Brazil | None |
|
| Checks that the annotated character sequence represents a Brazilian individual taxpayer registry number (Cadastro de Pessoa Fídsica) | Brazil | None |
|
| Checks that the annotated character sequence represents a Brazilian voter ID card number (Título Eleitoral) | Brazil | None |
In some cases neither the Bean Validation constraints nor the custom constraints provided by Hibernate Validator will fulfill your requirements. In this case you can easily write your own constraint. You can find more information in Chapter 6, Creating custom constraints.