Running your first Jakarta Bean Validation 2.0 code

Jakarta Bean Validation is a Java specification that basically helps you to protect your data. Through its API, you can validate fields and parameters, express constraints using annotations, and extend your customs validation rules.

It can be used both with Java SE and Jakarta EE.

In this recipe, you will have a glimpse of Jakarta Bean Validation 2.0. It doesn't matter whether you are new to it or are already using version 1.1; this content will help to familiarize you with some of its new features.

Getting ready

First, you need to add the right Jakarta Bean Validation dependency to your project, as follows:

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.hibernate.validator</groupId>
        <artifactId>hibernate-validator</artifactId>
        <version>6.0.15.Final</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish</groupId>
        <artifactId>javax.el</artifactId>
        <version>3.0.1-b11</version>
    </dependency>
</dependencies>

How to do it...

We need to perform the following steps to try this recipe:

1. First, we need to create an object with some fields to be validated:

public class User {

    @NotBlank
    private String name;
    
    @Email
    private String email;
    
    @NotEmpty
    private List<@PositiveOrZero Integer> profileId;

    
    public User(String name, String email, List<Integer> profileId) {
        this.name = name;
        this.email = email;
        this.profileId = profileId;
    }
}

2. Then, we create a UserTest class to validate those constraints:

public class UserTest {
 
    private static Validator validator;
 
    @BeforeClass
    public static void setUpClass() {
        validator = Validation.buildDefaultValidatorFactory()
        .getValidator();
    }
 
    @Test
    public void validUser() {
        User user = new User(
            "elder", 
            "[e-mail]", 
            asList(1,2));
 
            Set<ConstraintViolation<User>> cv = validator
            .validate(user);
            assertTrue(cv.isEmpty());
    }
 
    @Test
    public void invalidName() {
        User user = new User(
            "", 
            "[e-mail]", 
            asList(1,2));
 
            Set<ConstraintViolation<User>> cv = validator
            .validate(user);
            assertEquals(1, cv.size());
    }

    @Test
    public void invalidEmail() {
        User user = new User(
        "elder",

        "elder-eldermoraes_com", 
        asList(1,2));
 
        Set<ConstraintViolation<User>> cv = validator
        .validate(user);
        assertEquals(1, cv.size());
    } 
 
    @Test
    public void invalidId() {
        User user = new User(
            "elder", 
            "[e-mail]", 
            asList(-1,-2,1,2));
 
            Set<ConstraintViolation<User>> cv = validator
            .validate(user);
            assertEquals(2, cv.size());
    } 
}

After this, let's see how the recipe works.

How it works...

Our User class uses four of the new constraints introduced by Jakarta Bean Validation 2.0:

• @NotBlank: This ensures that the value is not null, empty, or an empty string (it trims the value before evaluation, to make sure there aren't spaces).
• @Email: This allows only a valid email format. Forget those crazy JavaScript functions!
• @NotEmpty: This ensures that a list has at least one item.
• @PositiveOrZero: This guarantees that a number is equal to or greater than zero.

Then, we create a test class (using JUnit) to test our validations. It first instantiates Validator, as follows:

@BeforeClass
public static void setUpClass() {
    validator = Validation.buildDefaultValidatorFactory().getValidator();
}

Validator is an API that validates beans according to the constraints defined for them.

Our first test method tests a valid user, which is a User object that has the following:

• Name not empty
• Valid email
• A profileId list only with integers greater than zero

This is shown in the following code snippet:

User user = new User(
   "elder", 
   "[e-mail]", 
   asList(1,2));

And finally, we have the validation:

Set<ConstraintViolation<User>> cv = validator.validate(user);

The validate() method from Validator returns a set of constraint violations found, if any, or an empty set if there are no violations at all.

So, for a valid user, it should return an empty set:

assertTrue(cv.isEmpty());

For the other methods that work with variations around this model, we have the following:

• invalidName(): Uses an empty name
• invalidEmail(): Uses a malformed email
• invalidId(): Adds some negative numbers to the list

Note that the invalidId() method adds two negative numbers to the list:

asList(-1,-2,1,2));

So, we expect two constraint violations:

assertEquals(2, cv.size());

In other words, Validator checks not only the constraints violated, but how many times they are violated.

See also

• You can check the Jakarta Bean Validation 2.0 specification at http://beanvalidation.org/2.0/spec/.
• The full source code of this recipe is at https://github.com/eldermoraes/javaee8-cookbook/tree/master/chapter01/ch01-beanvalidation/.