Chapter 1. Getting started

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)

1.1. Project set up

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

Example 1.1. Hibernate Validator Maven dependency


<dependency>

    <groupId>org.hibernate</groupId>

    <artifactId>hibernate-validator</artifactId>

    <version>5.0.3.Final</version>

</dependency>

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

Hibernate Validator requires an implementation of the Unified Expression Language (JSR 341) for evaluating dynamic expressions in constraint violation messages (see Section 4.1, “Default message interpolation”). When your application runs in a Java EE container such as JBoss AS, an EL implementation is already provided by the container. In a Java SE environment, however, you have to add an implementation as dependency to your POM file. For instance you can add the following two dependencies to use the JSR 341 reference implementation:

Example 1.2. Maven dependencies for Unified EL reference implementation


<dependency>

    <groupId>javax.el</groupId>

    <artifactId>javax.el-api</artifactId>

    <version>2.2.4</version>

</dependency>

<dependency>

    <groupId>org.glassfish.web</groupId>

    <artifactId>javax.el</artifactId>

    <version>2.2.4</version>

</dependency>

1.1.2. CDI

Bean Validation defines integration points with CDI (Contexts and Dependency Injection for Java^TM EE, JSR 346). If your application runs in an environment which does not provide this integration out of the box, you may use the Hibernate Validator CDI portable extension by adding the following Maven dependency to your POM:

Example 1.3. Hibernate Validator CDI portable extension Maven dependency


<dependency>

    <groupId>org.hibernate</groupId>

    <artifactId>hibernate-validator-cdi</artifactId>

    <version>5.0.3.Final</version>

</dependency>

Note that adding this dependency is usually not required for applications running on a Java EE application server. You can learn more about the integration of Bean Validation and CDI in Section 10.3, “CDI”.

1.2. Applying constraints

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

Example 1.4. Class Car annotated with constraints

package org.hibernate.validator.referenceguide.chapter01;


import javax.validation.constraints.Min;

import javax.validation.constraints.NotNull;

import javax.validation.constraints.Size;


public class Car {


    @NotNull

    private String manufacturer;


    @NotNull

    @Size(min = 2, max = 14)

    private String licensePlate;


    @Min(2)

    private int seatCount;


    public Car(String manufacturer, String licencePlate, int seatCount) {

        this.manufacturer = manufacturer;

        this.licensePlate = licencePlate;

        this.seatCount = seatCount;

    }


    //getters and setters ...

}

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

manufacturer must never be null

licensePlate must never be null and must be between 2 and 14 characters long

seatCount must be at least 2
Tip
You can find the complete source code of all examples used in this reference guide in the Hibernate Validator source repository on GitHub.

1.3. Validating constraints

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

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.

1.4. Where to go next?

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 in Chapter 13, Further reading.

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