Exception Handling with RESTEasy's client proxy framework

[olze oli]

Hi, i would like to use resteasys client proxy framework as its nice to have an interface to communicate with.
My interface on the server side looks like:

@Path("/users")
public class UserRessource {

    private final UserService userService;
    private final CaptchaService captchaService;

    public UserRessource(UserService userService, CaptchaService captchaService) {
        this.userService = userService;
        this.captchaService = captchaService;
    }

    @POST
    @Consumes(MediaType.APPLICATION_JSON)
    @Produces(MediaType.APPLICATION_JSON)
    @Path("/")
    public Response registerUser(RegisterUserCommand cmd) throws InvalidCaptcha, RegistrationAlreadyWaitingForApproval, InvalidEmail {
        final String user = userService.registerUser(cmd);
        return Response.status(Response.Status.CREATED).entity(user).build();
    }
}

The code on the client (interface definition) is:

public interface SimpleClient {

    @POST
    @Path("/users")
    @Consumes(MediaType.APPLICATION_JSON)
    @Produces(MediaType.APPLICATION_JSON)
    public Response registerUser(RegisterUserCommand cmd) throws InvalidCaptcha, RegistrationAlreadyWaitingForApproval, InvalidEmail;
}

The client code is:

private final ResteasyClient client;
    private final ResteasyWebTarget target;
    private final SimpleClient simple;

    public RegisterForm() {
        //ClientConfiguration config  = new ClientConfiguration(new LocalResteasyProviderFactory(null));
        //config.register(new ExceptionMapperInvalidCaptcha());
        //client = new ResteasyClientBuilder().withConfig(config).build();
        client = new ResteasyClientBuilder().build();
        target = client.target("http://localhost:8081");
        simple = target.proxy(SimpleClient.class);
        client.getConfiguration();
       Response response = simple.registerUser(new RegisterUserCommand(username, name, password,
                ip, Integer.toString(Page.getCurrent().getWebBrowser().hashCode()), captcha));
            response.close();
    }

When i try to use the client, i do not get an exception as expected. The server throws the exception and puts it into the responses entity. This is working as expected. But on the client side, it seems like the exception is simply ignored. I would at least expect a string representation inside the response's entity of the exception. But there is nothing, it is null.
So i tried to tell resteasy it should use my exceptionmapper (the lines above which are commented), but that does not work neither. I did not find any documentation how to create such a (valid) ClientConfiguration.
The exceptionmapper i created is:

@Provider
public class ExceptionMapperInvalidCaptcha implements ExceptionMapper<InvalidCaptcha>{

    @Override
    public Response toResponse(InvalidCaptcha e) {
        return Response.status(Response.Status.BAD_REQUEST).
                entity(e).
                build();
    }
}

Can someone tell me how i can register this mapper so i can use the client code like this:

try {
            Response response = simple.registerUser(new RegisterUserCommand(username, name, password,
                ip, Integer.toString(Page.getCurrent().getWebBrowser().hashCode()), captcha));
            response.close();
        } catch (RegistrationAlreadyWaitingForApproval ex) {
            Notification.show("Already waiting for approval.", Notification.Type.ERROR_MESSAGE);
        } catch (InvalidCaptcha ex) {
            Notification.show("Wrong captcha.", Notification.Type.ERROR_MESSAGE);
        } catch (InvalidEmail ex) {
            Notification.show("invalid email " + ex.getLocalizedMessage());
        } catch (Exception ex) {
            System.out.println(ex);
        }

Thanks in advance!

[Rob Spoor]

Unfortunately, RESTeasy, Jersey and probably any JAX-RS implementation does not handle server side exceptions the way we would like to. Instead, the code throws an implementation specific exception. In RESTeasy that's (I think) a RedirectionException (3xx), a ClientErrorException (4xx) or a ServerErrorException (5xx). For all, you can get the response from the exception, which you may need to parse to convert into the original exception. Using an ExceptionMapper makes that step easier because you can turn exceptions into responses you can more easily convert back.

[olze oli]

Thanks Rob, can you show me how to register (or where) the ClientErrorException in the client? I use Vaadin as UI technology with jetty. I guess i have to have something like:

 client = new ResteasyClientBuilder().build();
        target = client.target("http://localhost:8081");
        target.register(new ExceptionMapperInvalidCaptcha());

But it is not running into the ExceptionMapper:

@Provider
public class ExceptionMapperInvalidCaptcha implements ExceptionMapper<InvalidCaptcha>{

    @Override
    public Response toResponse(InvalidCaptcha e) {
        return Response.status(Response.Status.BAD_REQUEST).
                entity(e).
                build();
    }

}

Any idea why? Did i register the mapper wrong? I would prefer to configure all this in java, not in .xml, if possible.

[olze oli]

I also tried to use ClientErrorException for the Mapper - but its also not executing it. Also the log shows nothing of that class, what i would expect when it gets registered

[Rob Spoor]

ExceptionMapper is a server-side mechanism - it turns an exception into a response. On the client side it no longer exists. You will need to catch the ClientErrorException separately, and manually convert it back to the proper exception (convert the response back into an exception). There is no mechanism for that in JAX-RS.

[olze oli]

Thanks, but how? The response's entity is null.

The code on the server is:

@Provider
public class InvalidCaptchaExceptionHandler implements ExceptionMapper<InvalidCaptcha> {
    @Override
    public Response toResponse(InvalidCaptcha exception) {
        return Response.serverError().status(Response.Status.BAD_REQUEST).entity("Invalid Captcha!").build();
    }
}

This is executed as expected.
But on the client side when i set a breakpoint after:

Response response = simple.registerUser(new RegisterUserCommand(username, name, password,
                ip, Integer.toString(Page.getCurrent().getWebBrowser().hashCode()), captcha));
            response.close(); //<-- breakpoint here

I see nothing of "Invalid Captcha" in the response to identify what has caused it on the server side. The entity is null. And i dont know why. This is my main problem. Can you tell me why?

[Rob Spoor]

Are you sure it's really null when you retrieve it? The response's entity may be lazily loaded. What happens if you try to actually retrieve the entity using response.getEntity()?

[olze oli]

response.getEntity() also returns null