Spring annotation method purpose

Question

I write simple validation annotation for spring project. Problem is that I don't understand some method purpose. Here is my annotation:

@Constraint(validatedBy = PostCodeValidator.class)
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface PostCode {
    public String value() default "LUV";
    public String message() default "must start with LUV";
    public Class<?>[] groups() default {};
    public Class<? extends Payload>[] payload() default {};

}

Could anyone explain me groups() & payload() method purpose? I'll be very grateful if explanation will be as simple as it possible. Thanks.

Answer 1

1) In Bean Validation Api, groups are used for selecting which fields of bean will be validated. Example : a User with Address property.

public class User {
    @NotNull(groups = GroupUser.class)
    String firstname;
    @NotNull(groups = GroupAddress.class)
    String street;
    @NotNull(groups = GroupAddress.class)
    String city;
}

To validate the whole user you can do :

Set<ConstraintViolation<User>> constraintViolations = validator.validate(user, GroupUser.class, GroupAddress.class);

To validate only the user information without address part you can use :

Set<ConstraintViolation<User>> constraintViolations = validator.validate(user, GroupUserName.class);

2) Payload is used to manage the severity level of error. You can implement Payload interface :

public class Severity {
    public static class Info implements Payload {}
    public static class Error implements Payload {}
}

If you annotate the firstname field with :

@NotNull(payload = {Severity.Error.class})

Then after validation you can add some logic by severity :

for (ConstraintViolation<TestBean> violation : constraintViolations) {
    Set<Class<? extends Payload>> payloads = violation.getConstraintDescriptor().getPayload();
    for (Class<? extends Payload> payload : payloads) {
        if (payload == Severity.Error.class) {
            // logic here   
        }
    }
}