How do I validate my DWR @RemoteMethod input objects?

Question

I’m using DWR 3.0.0-rc2 and Spring 3.1.1.RELEASE.  I was wondering if its possible to validate my @DataTransferObject input object using the Spring style “@Valid” (javax.validation.Valid) annotation.  My specific question is, if this is possible and I set up my remote call like so …

@RemoteMethod
@Override
public String myRemoteMethod(@Valid final MyDto request)
{

how do I test to see if the input object (request) is valid and then throw a corresponding set of errors back to the client? Thanks, - Dave

Answer 1

This looks like a good case to apply some AOP. One way is to create a @Before aspect that inspects the called arguments to see if they are annotated with @Valid, and if so trigger the validation for that argument and treat the results.

The code of this aspect would look like this:

@Aspect
public class ValidatingAspect {

    Validator validator;

    public ValidatingAspect() {
        Configuration<?> configuration = Validation.byDefaultProvider().configure();
        ValidatorFactory factory = configuration.buildValidatorFactory();
        this.validator = factory.getValidator();    
    }

    @Before("execution(* com.yourpackage..*.*(..))")
    public void validateBefore(JoinPoint jp) throws Throwable {
        Object[] args = jp.getArgs();
        MethodSignature ms = (MethodSignature) jp.getSignature();
        Method m = ms.getMethod();

        Annotation[][] parameterAnnotations = m.getParameterAnnotations();

        for (int i = 0; i < parameterAnnotations.length; i++) {
            Annotation[] annotations = parameterAnnotations[i];
            for (Annotation annotation : annotations) {
                if (annotation.annotationType() == Valid.class) {
                    Set<ConstraintViolation<T>> constraintViolations =  validator.validate(jp.getArgs()[i]); 
                       ... handle validation results ...
                }
            }
        }
    } 
}