GWT RPC how to send any Object

I have a question concer开发者_JAVA技巧ning GWT RPC and self made classes.

So I create class for GWT like

public class B IsSerializable
{
public B(){}
private String b;
public B(String b)
{
this.b=b;
}

public String getB(){return this.b;}

}

And I want to sent the class to the GWT servlet. So I create method in servlet like a

public class TestService extends RemoteServiceServlet{

    public String getServerReply(int a, B b)
    {
    return b.getB()+" and hello from server";
    }
}

But I always get thrown exception in AsyncCallback method like

public void onFailure(Throwable caught) {

 }

So I am confused and ask how to send B class to server?

I am looking forward to your advices

TestService(client-side):

public interface TestService extends RemoteService {
    public B getString();
}

TestServiceAsync(client-side):

public interface TestServiceAsync {
    public void getString(AsyncCallback<B> callback);
}

TestServiceImpl(server-side);

public class TestServiceImpl extends RemoteServiceServlet implements TestService {
    public B getString() {
        return new B("Some String from the server");
    }
}

Making the call and doing somethinbg with the message:

TestServiceAsync service=(TestServiceAsync) GWT.create(TestService.class);
AsyncCallback<B> callback=new AsyncCallback<B>() {
    public void onFailure(Throwable caught) {
        Window.alert(caught.toString());
    }
    public void onSuccess(B result) {
        Window.alert(result.getString());//Will show "Some String from the server"
    }
}
service.getString(callback);

You need three files to make GWT-RPC work, 2 Interfaces(...Service and ...ServiceAsync) on the client and 1 class(...ServiceImpl) on the server.

Thanks :)

I know there should be 2 client side interfaces and so I did... And finally I succeeded to send B and to get a server reply The thing was

A) I forgot to implement the client service interface to my servlet (so the call was blocked)

B) I had to modify my B type into a client one

--Server side--

public String getServerReply(int a, com.mycompany.project.client.B b) 
{ return b.getB()+" and hello from server"; } 

And that worked fine :) But I haven't checked is the getB() is null but first step is done as I hope successfully :)