GWT - No answer from CallBack from REST Service

Question

I have my REST service : http://localhost:4242/myrestservice/getobject which returns some JSON data

Then, i have my GWT client : http://localhost:4242/gwtclient that client is supposed to do Async calls to the REST service.

Im pretty new to this, so my first idea was to do the following :

RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, URL.encode("http://localhost:4242/myrestservice/getobject"));
builder.setHeader("Accept", "application/json");
builder.setCallback(new MyObjectDescCallback());    
builder.setRequestData("");
Request req  = builder.send();

...

final class MyObjectDescCallback implements RequestCallback {
            public void onError(Request request, Throwable exception) {
                showAlert("error = "+exception.getMessage());

                GWT.log(exception.getMessage());
       }
            public void onResponseReceived(Request request, Response response) {
showAlert("response = " + response.getStatusCode());
//Do my stuff here
}
}
}

Unfortunately,i get no response.

I checked on the Rest service, and it does send the object

It seems that my GWT app doesnt receive the answer.

Any idea how to make it work ?

UPDATE

Here are my results with Firebug :

Response Headers
Server  Apache-Coyote/1.1
Content-Type    application/json
Transfer-Encoding   chunked
Date    Sun, 24 Apr 2011 11:04:15 GMT

Request Headers
Host    127.0.0.1:4242
User-Agent  Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0) Gecko/20100101 Firefox/4.0
Accept  application/json
Accept-Language en-us,en;q=0.5
Accept-Encoding gzip, deflate
Accept-Charset  ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive  115
Connection  keep-alive
Referer http://localhost:4242/gwtclient/gwtclient.html
Origin  http://localhost:4242

But i get response.getStatusCode() = 0 and empty response !

UPDATE 2 :

I feel so dumb now...

The issue was in fact SOP ...

I was using the URL localhost, but in my code i was using 127.0.0.1 !

Damn....

Answer 1

You say you want to use a Async callback but you never use new AsyncCallback<string>() in your code. This is how I make async calls to a server with my gwt application: (I don't use JSON but that doesn't really matter here I think)

request object = new request();
object.getMessageXml("test.php", "GET", null, new AsyncCallback<String>() {

    @Override
    public void onFailure(Throwable caught) {
        //error handling
    }

    @Override
    public void onSuccess(String result) {
        // do some stuff with the result
    }
});

And this is the request class:

public void getMessageXml(String file, String type, String requestData, final AsyncCallback<String> callback) {

        RootLayoutPanel.get().addStyleName("loading");

        final String url = "test/" + file;
        RequestBuilder rb;

        try {
            if(type == "POST") {
                rb = new RequestBuilder(RequestBuilder.POST, URL.encode(url));
            }
            else {
                rb = new RequestBuilder(RequestBuilder.GET, URL.encode(url));
            }

            rb.setHeader("Content-Type", "application/x-javascript; charset:ISO-8859-1");
            rb.sendRequest(requestData, new RequestCallback() {

                @Override
                public void onResponseReceived(Request request, Response response) {

                    if(Response.SC_OK == response.getStatusCode()) {

                        callback.onSuccess(response.getText()); 
                    }
                    else {
                        //error 
                    }
                    RootLayoutPanel.get().removeStyleName("loading");   
                }

                @Override
                public void onError(Request request, Throwable exception) { 
                    callback.onFailure(exception);
                }   
            }); 
        }
        catch(RequestException rex) {
            callback.onFailure(rex);
        }   
    }

[EDIT:] Maybe you find something here: