GET request using GWT to retrieve XML data?

Oh hello there, fellow SO members,

I have a web service that returns XML data using a simple get request that goes like this :

http://my-service:8082/qc/getData?paramX=0169&paramY=2

the service returns raw xml in the page according to the parameters' values.

I am trying to retrieve this data from a GET request in GWT using RequestBuilder, Request, etc. However, the response gives me empty text, a Status code of ZERO (which doesn't mean anything and isn't supposed to happen), and so on.

Here's the simplified code that doesn't work.

public class SimpleXML implements EntryPoint {

public void onModuleLoad() {

    this.doGet("http://my-service:8082/qc/getData", "0169", "2");
}

public void doGet(String serviceURL, String paramX, String paramY) {
    final String getUrl = serviceURL + "?paramX=" + paramX + "&idTarification=" + paramY;

    RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, getUrl);

    try {
         Request response = builder.sendRequest(null, new RequestCallback() {

            @Override
            public void onResponseReceived(Request request, Response response) {
                response.getStatusCode(); // Gives me 0 (zero)  :(
            }

            @Override
            public void onError(Request request, Throwable exception) {
                // ... doesn't matter for this example
            }
        });
    } catch (RequestException e) {
        // ... doesn't matter for this example
    }
}

}

I don't get why this wouldn't work, since this is REALLY simple, I've seen tutorials and they all show me this way of doing things..

Thanks in advance

Solution

The reason is, that browsers do not allow cross-site requests with AJAX (see Same Origin Policy).

This means, that you can only call a service on the same server, same port (using the same protocol) as your HTML page. If you want to perform cross-site requests, you can use JSONP, as explained in http://code.google.com/webtoolkit/doc/latest/tutorial/Xsite.html.