Sending messages in GWT by Errai framework

Question

here you can see how to send a message from client.

I have a client HelloServer.java, when i click on the button I want to send message to a server.

package gwt.user.client;

import org.jboss.errai.bus.client.ErraiBus;
import org.jboss.errai.bus.client.api.base.CommandMessage;
import org.jboss.errai.bus.client.api.base.MessageBuilder;
import org.jboss.errai.bus.client.api.messaging.Message;
import org.jboss.errai.bus.client.api.messaging.MessageBus;
import org.jboss.errai.bus.client.api.messaging.MessageCallback;
import org.jboss.errai.bus.client.api.messaging.RequestDispatcher;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.rpc.ServiceDefTarget;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.DialogBox;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.VerticalPanel;

public class HelloServer implements EntryPoint{

    private MyTable table;
    private MessageBus bus = ErraiBus.get();
    private RequestDispatcher dispatcher = ErraiBus.getDispatcher();
    UserService usrSer;

    private RequestDispatcher getDispatcher(){
        return this.dispatcher;
    }

      public void onModuleLoad() {

        table = new MyTable(null);

        Button button = new Button("Click me");

        // We can add style names
        button.addStyleName("pc-template-btn");
        // or we can set an id on a specific element for styling

        VerticalPanel vPanel = new VerticalPanel();
        vPanel.setWidth("100%");
        vPanel.setHorizontalAlignment(VerticalPanel.ALIGN_CENTER);
        vPanel.add(button);

        vPanel.add(table);

        // add table and button to the RootPanel
        RootPanel.get().add(vPanel);

        // create the dialog box
        final DialogBox dialogBox = new DialogBox();
        dialogBox.setText("Welcome to GWT Server Communication!");
        dialogBox.setAnimationEnabled(true);
        Button closeButton = new Button("close");
        VerticalPanel dialogVPanel = new VerticalPanel();
        dialogVPanel.setWidth("100%");
        dialogVPanel.setHorizontalAlignment(VerticalPanel.ALIGN_CENTER);
        dialogVPanel.add(closeButton);

        closeButton.addClickHandler(new ClickHandler() {
          @Override
          public void onClick(ClickEvent event) {
            dialogBox.hide();
          }
        });

        // Set the contents of the Widget
        dialogBox.setWidget(dialogVPanel);

        button.addClickHandler(new ClickHandler() {
          @Override
          public void onClick(ClickEvent event) {
            UserServiceAsync service = (UserServiceAsync) GWT.create(UserService.class);
            ServiceDefTarget serviceDef = (ServiceDefTarget) service;
            serviceDef.setServiceEntryPoint(GWT.getModuleBaseURL() + "userService");
            UserCallback myUserCallback = new UserCallback(table);

            MessageBuilder.createMessage()
              .toSubject("UserServiceImpl") // (1)
              .signalling() // (2)
              .noErrorHandling() // (3)
              .sendNowWith(getDispatcher()); // (4)

            service.getUserList(myUserCallback);
          }
        });

      }

}

UserServiceImpl.java is the server where I want to receive the message in callback method.

package gwt.user.server;

import gwt.user.client.User;
import gwt.user.client.UserService;

import java.util.ArrayList;
import java.util.List;

import org.jboss.errai.bus.client.api.base.CommandMessage;
import org.jboss.errai.bus.client.api.messaging.Message;
import org.jboss.errai.bus.client.api.messaging.MessageCallback;
import org.jboss.errai.bus.server.annotations.Service;

import com.google.gwt.user.server.rpc.RemoteServiceServlet;

@Service
public class UserServiceImpl extends RemoteServiceServlet implements UserService, MessageCallback {

    private static final long serialVersionUID = 1L;

    private List<User> userList = new ArrayList<User>();

    public UserServiceImpl() {

        User user = new User();
        user.setId("1");
        user.setUsername("Peter");
        user.setNumberOfHits("15");
        userList.add(user);

        user = new User();
        user.setId("2");
        user.setUsername("Hanz");
        user.setNumberOfHits("25");
        userList.add(user);

    }

    public User getUser(String id) {

        for (Object object : userList) {
          if (((User) object).getId().equals(id))
            return ((User) object);
        }
        return null;

    }

    public List<User> getUserList() {
        return userList;
    }

    @Override
    public void callback(Message message) {
        System.out.print("Message received");
    }

    public void callback(CommandMessage message) {
        System.out.print("Message received");
      }
} 

When I click the button I get no subscribers to deliver error message:

org.jboss.errai.bus.client.api.base.NoSubscribersToDeliverTo: no subscribers to deliver to for subject: UserServiceImpl
  org.jboss.errai.bus.client.framework.ClientMessageBusImpl.send(ClientMessageBusImpl.java:812)
  org.jboss.errai.bus.client.ErraiBus$3.dispatch(ErraiBus.java:171)
  org.jboss.errai.bus.client.api.base.CommandMessage.sendNowWith(CommandMessage.java:349)
  org.jboss.errai.bus.client.api.base.DefaultMessageBuilder$1.sendNowWith(DefaultMessageBuilder.java:95)
  gwt.user.client.HelloServer$2.onClick(HelloServer.java:84)

If I annotate UserServiceImpl.java class with @Service("UserServiceImpl"), it doesn't help and I get the same error.

When I add

bus.subscribe("UserServiceImpl", new UserServiceImpl());

before MessageBuilder.createMessage() in HelloServer.java

I get error message

[ERROR] No source code is available for type gwt.user.server.UserServiceImpl; did you forget to inherit a required module?

Does anybody know how to use messaging between Client and Server in GWT applications or show me a basic example?

Answer 1

Answer is in this thread. I forgot to add ErraiApp.properties file.