No Source Code is available for type : GWT Compilation Error

Question

I am trying to make get requests by a servlet in my GWT application. On compiling the code I am getting these errors.

[ERROR] Line 16: No source code is available for type org.apache.http.client.ClientProtocolException; did you forget to inherit a required module?
[ERROR] Line 16: No source code is available for type org.apache.http.ParseException; did you forget to inherit a required module?
[ERROR] Line 16: No source code is available for type org.json.simple.parser.ParseException; did you forget to inherit a required module?

What should I do to remove these errors? Are these classes are not supported by GWT?

Following is the code I am using

public String getJSON() throws ClientProtocolException, IOException, ParseException{
    HttpClient httpclient = new DefaultHttpClient(); 
    JSONParser parser = new JSONParser();
    String url = "some - url - can't disclose";
    HttpResponse response = httpclient.execute(new HttpGet(url));
    JSONObject json_data = (JSONObject)parser.parse(EntityUtils.toString(response.getEntity()));
    JSONArray results = (JSONArray)json_data.get("result");
}

This code is working fine If I use this on a usual java project/ console application.

Answer 1

Java code running in GWT is translated to Javascript, so some classes that work on a JVM won't work with GWT. The HttpClient and related classes are written to work on a JVM with full support for opening sockets, something that isn't allowed in a web browser, so these classes cannot be used.

To open a connection to the server you are using (subject to the browser Same Origin Policy), consider the RequestBuilder class, which allows you to provide a url and an HTTP method, and optionally headers, parameters, data, etc. This class is an abstraction over the XmlHttpRequest object in JavaScript, commonly used for AJAX requests in plain JS.