GWT 2.5 easy Bean validation

The goal of this paper is to setup quickly and smoothly a clean validation process on your DTO. It shows an easy setup using GIN and GWT-Dispatch. An Intro is also available here Gwt 2.5 Validation Intro

The needed libraires to start are: Javax validation (Api), Hibernate validators (Sources and Implementation) and Slf4j (logger).
For the next step we are going to build a custom annotation which will be use into our gwt-dispatch actions:
Here the code for custom validator and his annotation:

@Target({ ElementType.FIELD, ElementType.ANNOTATION_TYPE })
@Constraint(validatedBy = RequiredValidator.class)
public @interface Required {
    String message() default "Value is required";
    Class[] groups() default {};
    Class[] payload() default {};


public class RequiredValidator implements ConstraintValidator {
    public void initialize(Required constraintAnnotation) { }

    public boolean isValid(String value, ConstraintValidatorContext context) {
        return (!Strings.isNullOrEmpty(value));
        // use Guava strings to check null or empty value

Now we can use our required annotation into our action (There is also a possibility to use more than one annotation on our field):

public class SendMailAction extends ActionImpl {
    private String email;
    private SendMailAction(String email) { = email;
  // add accessors

To complete module settings we need a validator factory for the module like it is shown into the Gwt Devguide:

public final class ClientValidatorFactory extends AbstractGwtValidatorFactory {

    // Syntax for multiple class:  @GwtValidation({action1.class, action2.class})
    public interface GwtValidator extends Validator {
    public AbstractGwtValidator createValidator() {
        return GWT.create(GwtValidator.class);

Now we are going to write a generic constraint validation manager which will be provided using Gin Injector. Here it is :

public class ClientValidation extends Validation {
    private Validator validator;
    private Set<ConstraintViolation> constraintViolations;

    public ClientValidation() {
        this.validator = buildDefaultValidatorFactory().getValidator();
    public Set<ConstraintViolation> getConstraintViolations(Object object) {
        this.constraintViolations = validator.validate(object);
        return constraintViolations;
    public String getPrimaryMessage() {
        return constraintViolations.iterator().next().getMessage();

Finally we can configure one single instance into our module:


and use it everywhere on client side with @Inject:

if (!clientValidation.getConstraintViolations(new sendMailAction(email)).isEmpty()) {
} else {
    // do something

Thanks to the GWT team for those enhancements for client side validation.