Basic use of gwt-comet for GWT

Question

I'm trying out the gwt-comet extension here. I cant get any messages from the server to the client.

I have a basic GWT application with a RPC service implementation.

Client: MockGui.java

public class MockGui implements EntryPoint {
    @SerialTypes({
        Message.class
    })

    public static abstract class MyMessageSerializer extends CometSerializer {
    }

    public void onModuleLoad() {
    ...

        goServer();
    }

    public void goServer() {
        GreetingServiceAsync service = GWT.create(GreetingService.class);
        service.greetServer(new Message(), new AsyncCallback<Void>() {

            @Override
            public void onSuccess(Void result) {
                // TODO Auto-generated method stub

            }

            @Override
            public void onFailure(Throwable caught) {
                // TODO Auto-generated method stub

            }
        });

        CometListener listener = new CometListener() {
            public void onConnected(int heartbeat) {
            }

            public void onDisconnected() {
            }

            public void onHeartbeat() {
            }

            public void onRefresh() {
            }

            public void onError(Throwable exception, boolean connected) {
               // warn the user of the connection error
            }

            public void onMessage(List<? extends Serializable> messages) {
                for (Serializable message : messages) {
                    if (message.getClass().equals(Message.class)) {
                        Message myMessage = (Message) message;
                        Window.alert(myMessage .getMessage());

                        Log.info("This is a 'INFO' test message");
                        Log.warn("This is a 'WARN' test message");
                    }
                }
            }
        };

        String serverUrl = GWT.getModuleBaseURL() + "greet";

        CometSerializer serializer = GWT.create(MyMessageSerializer.class);

        CometClient client = new CometClient(serverUrl, serializer, listener);

        client.start();
}

Server: GreetingServiceImpl.java

public class GreetingServiceImpl extends RemoteServiceServlet implements
        GreetingService {
    List<Message> messages = new ArrayList<Message>();

    public void greetServer(Message message) throws IllegalArgumentException {
        HttpSession httpSession = getThreadLocalRequest().getSession();

        CometSession cometSession = CometServlet.getCometSession(httpSession);

        Message m = new Message();
        m.setMessage("test from server");

        cometSession.enqueue(m);
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>

    <!-- Servlets -->
    <servlet>
        <servlet-name>greetServlet</servlet-name>
        <servlet-class>test.mock.gui.server.GreetingServiceImpl</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>greetServlet</servlet-name>
        <url-pattern>/mockgui/greet</url-pattern>
    </servlet-mapping>

    <!-- the comet servlet for streaming messages to the client -->
    <servlet>
        <servlet-name>myComet</servlet-name>
        <servlet-class>net.zschech.gwt.comet.server.CometServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>myComet</servlet-name>
       <url-pattern>/mockgui/comet</url-pattern>
    </servlet-mapping>

    <!-- Default page to serve -->
    <welcome-file-list>
        <welcome-file>MockGui.html</welcome-file>
    </welcome-file-list>

</web-app>

I expect the comet listener on the client side (listener) to be triggered - yet, nothing seems to happen. I don't know how I can debug the problem any further - nothing fails to execute.

Is there any way I can see when the comet servlet (myComet) is triggered and what it's doing?

Answer 1

It seems this is the URL you are using for the comet request:

String serverUrl = GWT.getModuleBaseURL() + "greet";

But your comet URL in web.xml is /mockgui/comet. Can you at least try replacing the above line with this?:

String serverUrl = GWT.getModuleBaseURL() + "comet";

and if it still doesn't work, do a

Window.alert(serverUrl);

and see if the URL is actually pointing to the comet servlet.

Good luck!