Validating Combinations of Fields in JPA 2.0/Hibernate

When using JPA 2.0/Hibernate validation, it's possible to encounter scenarios where the validation of multiple fields in combination is necessary. For instance, consider a model with fields getValue1() and getValue2():

public class MyModel {
    public Integer getValue1() {
        //...
    }
    public String getValue2() {
        //...
    }
}

The model should be considered invalid if both getValue1() and getValue2() are null, indicating invalid data.

Class-Level Constraints: The Solution

To handle such validations, JPA 2.0/Hibernate provides class-level constraints. These constraints operate on the entire class instance instead of individual properties. This approach provides flexibility in validating interrelated fields.

Defining the Constraint

Define a class-level constraint named AddressAnnotation to validate the combination of fields. Set the @Target to ElementType.TYPE to apply this constraint to the class rather than a specific property:

@Constraint(validatedBy = MultiCountryAddressValidator.class)
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface AddressAnnotation {
    String message() default "{error.address}";
    Class>[] groups() default { };
    Class extends Payload>[] payload() default { };
}

Implementing the Validator

Next, create the validator implementation MultiCountryAddressValidator. This class will receive the object instance and perform the combined field validation:

public class MultiCountryAddressValidator implements ConstraintValidator {
    ...
    // Implement the isValid() method to define the validation logic
}

In this implementation, you can access multiple fields of the object instance (Address in this case) and apply necessary validation rules.

Annotating the Model Class

Finally, annotate your MyModel class with the AddressAnnotation:

@AddressAnnotation
public class MyModel {
    ...
}

By utilizing class-level constraints, you can effectively validate combinations of fields in a robust and flexible manner using Hibernate validation.