How to access a field which is described in annotation property

Question

Is it possible to access a field value, where field name is described in annotation which annotate another field in class.

For example:

@Entity
public class User {

    @NotBlank
    private String password;

    @Match(field = "password")
    private String passwordConfirmation;
}

Annotation:

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = FieldMatchValidator.class)
@Documented
public @interface Match {

    String message() default "{}";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};

    String field();
}

Now, is it possible to access field password from class User in ConstraintValidator implementaion class?

---

Edit:

I wrote something like this:

public class MatchValidator implements ConstraintValidator<Match, Object> {

private String mainField;
private String secondField;
private Class clazz;

@Override
public void initialize(final Match match) {
    clazz = User.class;

    final Field[] fields = clazz.getDeclaredFields();
    for (Field field : fields) {
        if (field.isAnnotationPresent(Match.class)) {
            mainField = field.getName();
        }
    }

    secondField = match.field();
}

@Override
public boolean isValid(final Object value, final ConstraintValidatorContext constraintValidatorContext) {
    try {
        Object o; //Now how to get the User entity instance?

        final Object firstObj = BeanUtils.getProperty(o, mainField);
        final Object secondObj = BeanUtils.getProperty(o, secondField);

        return firstObj == null && secondObj == null || firstObj != null && firstObj.equals(secondObj);
    } catch (final Exception ignore) {
        ignore.printStackTrace();
    }
    return true;
}
}

Now the question is how can I get the User object instance and compare fields values?

Answer 1

@Hardy Thenks for tip. Finally wrote some code which matches (more or less) expected result.

I'll paste it here, maybe will help someone to solve his problem.

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Match {

    String field();

    String message() default "";
}

---

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = MatchValidator.class)
@Documented
public @interface EnableMatchConstraint {

    String message() default "Fields must match!";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

---

public class MatchValidator implements  ConstraintValidator<EnableMatchConstraint, Object> {

    @Override
    public void initialize(final EnableMatchConstraint constraint) {}

    @Override
    public boolean isValid(final Object o, final ConstraintValidatorContext context) {
        boolean result = true;
        try {
            String mainField, secondField, message;
            Object firstObj, secondObj;

            final Class<?> clazz = o.getClass();
            final Field[] fields = clazz.getDeclaredFields();

            for (Field field : fields) {
                if (field.isAnnotationPresent(Match.class)) {
                    mainField = field.getName();
                    secondField = field.getAnnotation(Match.class).field();
                    message = field.getAnnotation(Match.class).message();

                    if (message == null || "".equals(message))
                        message = "Fields " + mainField + " and " + secondField + " must match!";

                    firstObj = BeanUtils.getProperty(o, mainField);
                    secondObj = BeanUtils.getProperty(o, secondField);

                    result = firstObj == null && secondObj == null || firstObj != null && firstObj.equals(secondObj);
                    if (!result) {
                        context.disableDefaultConstraintViolation();
                        context.buildConstraintViolationWithTemplate(message).addPropertyNode(mainField).addConstraintViolation();
                        break;
                    }
                }
            }
        } catch (final Exception e) {
            // ignore
            //e.printStackTrace();
        }
        return result;
    }
}

And how to use it...? Like this:

@Entity
@EnableMatchConstraint
public class User {

    @NotBlank
    private String password;

    @Match(field = "password")
    private String passwordConfirmation;
}