Duplicate Hibernate validation ConstraintViolations on Lombok’s @Data bean: A Comprehensive Guide

If you’re a Java developer working with Hibernate and Lombok, you might have stumbled upon an issue where duplicate ConstraintViolations are thrown when using Hibernate validation on a Lombok @Data bean. This issue can be frustrating, especially when you’re trying to implement robust validation in your application. In this article, we’ll dive into the root cause of the problem, explain how to reproduce it, and provide a step-by-step guide on how to fix it.

What is Lombok’s @Data annotation?

Lombok is a popular Java library that helps reduce boilerplate code in Java classes. One of its most useful features is the @Data annotation, which automatically generates getters, setters, and other boilerplate code for your Java classes. This annotation is particularly useful when working with POJOs (Plain Old Java Objects) that require basic getters and setters.

@Data
public class User {
    private String name;
    private String email;
    private int age;
}

In the above example, Lombok’s @Data annotation will generate getters and setters for the User class, making it easy to work with.

What is Hibernate validation?

Hibernate validation is a mechanism that allows you to validate Java beans using annotations. It provides a robust way to ensure that data conforms to specific rules and constraints, such as data type, length, and format. Hibernate validation is widely used in Java-based applications to ensure data consistency and integrity.

@Entity
public class User {
    @NotEmpty
    private String name;
    
    @Email
    private String email;
    
    @Min(18)
    private int age;
}

In the above example, Hibernate validation annotations such as @NotEmpty, @Email, and @Min are used to specify constraints on the User class. These constraints will be enforced when the object is validated using Hibernate’s Validator API.

The Problem: Duplicate ConstraintViolations

When you combine Lombok’s @Data annotation with Hibernate validation, you might encounter an issue where duplicate ConstraintViolations are thrown when validating an object. This occurs because Lombok’s @Data annotation generates getters and setters that interfere with Hibernate’s validation mechanism.

To reproduce the issue, create a simple Java class with Lombok’s @Data annotation and Hibernate validation annotations:

@Data
public class User {
    @NotEmpty
    private String name;
    
    @Email
    private String email;
    
    @Min(18)
    private int age;
}

Next, create a test class to validate the User object:

public class UserTest {
    @Test
    public void testValidation() {
        User user = new User();
        user.setName("");
        user.setEmail(" invalid_email");
        user.setAge(17);
        
        Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
        Set<ConstraintViolation<User>> violations = validator.validate(user);
        
        for (ConstraintViolation<User> violation : violations) {
            System.out.println(violation.getMessage());
        }
    }
}

When you run the test, you’ll notice that each constraint violation is reported twice. This is because Lombok’s @Data annotation generates getters and setters that are also being validated by Hibernate, resulting in duplicate ConstraintViolations.

Solution: Fixing Duplicate ConstraintViolations

To fix the duplicate ConstraintViolations issue, you need to tell Hibernate to ignore the getters and setters generated by Lombok’s @Data annotation. You can do this by using the @Accessible annotation on the getters and setters.

@Data
public class User {
    @NotEmpty
    @Accessible(Accessible.SET_PROPERTY)
    private String name;
    
    @Email
    @Accessible(Accessible.SET_PROPERTY)
    private String email;
    
    @Min(18)
    @Accessible(Accessible.SET_PROPERTY)
    private int age;
}

The @Accessible annotation tells Hibernate to only validate the properties themselves, ignoring the getters and setters generated by Lombok. By doing so, you ensure that each constraint violation is reported only once.

Additional Tips and Tricks

When working with Lombok and Hibernate validation, here are some additional tips and tricks to keep in mind:

• Make sure to use the correct version of Lombok and Hibernate validation. Incompatible versions can lead to unexpected behavior.
• Use the @Getter and @Setter annotations explicitly on individual fields to control which getters and setters are generated by Lombok.
• Consider using Lombok’s @Value annotation instead of @Data, which generates immutable objects with no setters.
• Use Hibernate’s @Valid annotation on your controller methods to enable automatic validation of incoming requests.

Conclusion

Duplicate ConstraintViolations on Lombok’s @Data bean can be a frustrating issue to deal with, but by understanding the root cause and applying the solution outlined in this article, you can ensure that your Hibernate validation works as expected. Remember to use the @Accessible annotation to tell Hibernate to ignore the getters and setters generated by Lombok, and keep in mind the additional tips and tricks mentioned above to make the most out of Lombok and Hibernate validation.

Keyword	Description
Lombok’s @Data annotation	Automatically generates getters, setters, and other boilerplate code for Java classes.
Hibernate validation	A mechanism that allows you to validate Java beans using annotations.
@Accessible annotation	Tells Hibernate to ignore getters and setters generated by Lombok.

I hope this article has been helpful in resolving the duplicate ConstraintViolations issue on Lombok’s @Data bean. If you have any further questions or need more assistance, feel free to ask in the comments below!

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