Java – GWT requestbuilder – cross site request

I'm trying to create a cross site request using the GWT request builder, but I can't make it work As you can see, this is a sample GWT project that I have completed https://developers.google.com/web-toolkit/doc/latest/tutorial/Xsite. But I still lack something

I publish the code here What did I miss?

package com.gwt.reqbuilder.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.http.client.Request;
import com.google.gwt.http.client.RequestBuilder;
import com.google.gwt.http.client.RequestCallback;
import com.google.gwt.http.client.RequestException;
import com.google.gwt.http.client.Response;
import com.google.gwt.http.client.URL;
import com.google.gwt.user.client.Window;

public class GWTRequestBuilder implements EntryPoint
{
    private static final String JSON_URL = "http://localhost:8000/?q=ABC&callback=callback125";
    public void onModuleLoad()
    {
        GWTPOSTHTTP();
    }

    public void GWTPOSTHTTP()
    {
        String postUrl="http://localhost:8000";
        String requestData="q=ABC&callback=callback125";
        RequestBuilder builder = new RequestBuilder(RequestBuilder.POST,postUrl);
        try {
            builder.sendRequest(requestData.toString(),new RequestCallback() 
            {
                public void onError(Request request,Throwable e) 
                {
                    Window.alert(e.getMessage());
                }
                public void onResponseReceived(Request request,Response response)
            {
                    if (200 == response.getStatusCode())
                    {
                        Window.alert(response.getText());
                    } else {
                        Window.alert("Received HTTP status code other than 200 : "+ response.getStatusText());
                    }
            }
            });
        } catch (RequestException e) {
            // Couldn't connect to server
        Window.alert(e.getMessage());
        }
    }
}

Solution

In fact, if we can set it in the servlet response header, we can issue cross site requests from GWT requestbuilder

Response.setHeader("Access-Control-Allow-Origin","http://myhttpserver");

It's cool. If someone needs GWT project and python servlet, please let me know and I can upload files

GWT Client Code : https://github.com/manikandaraj/MLabs/tree/master/GWT/GWTClient