java.lang.NoClassDefFoundError: org/apache/http/client/HttpClient

I am trying to make a get request from the GWT servlet to get JSON response from a web service.Following is the code in my servlet :

public String getQueData() throws IllegalArgumentException {    String message = null;    try {                   HttpClient httpclient = new DefaultHttpClient();         JSONParser parser = new JSONParser();        String url = "working - url";        HttpResponse response = null;        response = httpclient.execute(new HttpGet(url));        JSONObject json_data = null;        json_data = (JSONObject)parser.parse(EntityUtils.toString(response.getEntity()));        JSONArray results = (JSONArray)json_data.get("result");        for (Object queid : results) {            message = message.concat((String) ((JSONObject)queid).get("id"));            message = message.concat("\t");            message = message.concat((String) ((JSONObject)queid).get("owner"));            message = message.concat("\n");        }      } catch (Exception e) {    message = e.toString();    }    return message;}

Getting the following exception on trying to make get request from a GWT servlet.

java.lang.NoClassDefFoundError: org/apache/http/client/HttpClient    at java.lang.Class.getDeclaredConstructors0(Native Method)    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2389)    at java.lang.Class.getConstructor0(Class.java:2699)    at java.lang.Class.newInstance0(Class.java:326)    at java.lang.Class.newInstance(Class.java:308)    at org.mortbay.jetty.servlet.Holder.newInstance(Holder.java:153)    at org.mortbay.jetty.servlet.ServletHolder.initServlet(ServletHolder.java:428)    at org.mortbay.jetty.servlet.ServletHolder.getServlet(ServletHolder.java:339)    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)    at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:35)    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)    at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:60)    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)    at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:122)    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)    at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)    at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:78)    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)    at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:362)    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)    at org.mortbay.jetty.Server.handle(Server.java:326)    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)Caused by: java.lang.ClassNotFoundException: org.apache.http.client.HttpClient    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)    at java.security.AccessController.doPrivileged(Native Method)    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)    at com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:176)    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

What could be the possible cause of this exception?How it could be removed?

I am using jdk1.6.0_30 on ubuntu 10.04.