How to fetch access token in Google AppEngine (OAuth 2.0) us

package com.login.client;


import java.io.BufferedReader;


import java.io.ByteArrayInputStream;


import java.io.IOException;


import java.io.InputStream;


import java.io.InputStreamReader;


import java.net.MalformedURLException;


import java.net.URL;


import java.util.List;



import com.google.appengine.api.urlfetch.HTTPHeader;


import com.google.appengine.api.urlfetch.HTTPMethod;


import com.google.appengine.api.urlfetch.HTTPRequest;


import com.google.appengine.api.urlfetch.HTTPResponse;


import com.google.appengine.api.urlfetch.URLFetchService;


import com.google.appengine.api.urlfetch.URLFetchServiceFactory;



public class FetchUrl {

    private static String client_id = "<Client ID>";

    private static String client_secret = "<client_secret>";

    private static String redirectURL = "http://gfksgnbgfcv.appspot.com/index2.jsp";

    private static URLFetchService fetchService;

    public static String getParseValue(String code){

        HTTPResponse httpResponse=null;

         try {

        String urlStr="https://accounts.google.com/o/oauth2/token";

        URL url = new URL(urlStr);

        HTTPMethod method=HTTPMethod.POST;

        HTTPRequest httpRequest = new HTTPRequest(url,method);

        fetchService = URLFetchServiceFactory.getURLFetchService();

        httpRequest.setHeader(new HTTPHeader("Content-Type", "application/x-www-form-urlencoded"));

        httpRequest.setHeader(new HTTPHeader("Content-length", "250"));

        httpRequest.addHeader(new HTTPHeader("code", code));

        httpRequest.addHeader(new HTTPHeader("client_id", client_id));

        httpRequest.addHeader(new HTTPHeader("client_secret", client_secret));

        httpRequest.addHeader(new HTTPHeader("redirect_uri", redirectURL));

        httpRequest.addHeader(new HTTPHeader("scope", ""));

        httpRequest.addHeader(new HTTPHeader("grant_type", "authorization_code"));

      httpResponse = fetchService.fetch(httpRequest);

      InputStream in=getContentAsStream(httpResponse);

         BufferedReader reader = new BufferedReader( new InputStreamReader(in));

         String line;

         String output="";

         while ((line = reader.readLine()) != null) {

             output=output+line;

     }

     reader.close();

     return output;

         }catch(Exception e){

             e.printStackTrace();

             System.out.println(e.getMessage());

             return e.getMessage();

         }

         
    }

    public static byte[] getContentAsBytes(HTTPResponse httpResponse) {

       return httpResponse.getContent();

      }


      public static InputStream getContentAsStream(HTTPResponse httpResponse) {

       return new ByteArrayInputStream(getContentAsBytes(httpResponse));

      }

}
	
package com.login.client;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;

import com.google.appengine.api.urlfetch.HTTPHeader;
import com.google.appengine.api.urlfetch.HTTPMethod;
import com.google.appengine.api.urlfetch.HTTPRequest;
import com.google.appengine.api.urlfetch.HTTPResponse;
import com.google.appengine.api.urlfetch.URLFetchService;
import com.google.appengine.api.urlfetch.URLFetchServiceFactory;

public class FetchUrl {
	private static String client_id = "<Client ID>";
	private static String client_secret = "<client_secret>";
	private static String redirectURL = "http://gfksgnbgfcv.appspot.com/index2.jsp";
	private static URLFetchService fetchService;
	public static String getParseValue(String code){
		HTTPResponse httpResponse=null;
		  try {
		 String urlStr="https://accounts.google.com/o/oauth2/token";
		 URL url = new URL(urlStr);
		 HTTPMethod method=HTTPMethod.POST;
		 HTTPRequest httpRequest = new HTTPRequest(url,method);
		 fetchService = URLFetchServiceFactory.getURLFetchService();
		 httpRequest.setHeader(new HTTPHeader("Content-Type", "application/x-www-form-urlencoded"));
		 httpRequest.setHeader(new HTTPHeader("Content-length", "250"));
		 httpRequest.addHeader(new HTTPHeader("code", code));
		 httpRequest.addHeader(new HTTPHeader("client_id", client_id));
		 httpRequest.addHeader(new HTTPHeader("client_secret", client_secret));
		 httpRequest.addHeader(new HTTPHeader("redirect_uri", redirectURL));
		 httpRequest.addHeader(new HTTPHeader("scope", ""));
		 httpRequest.addHeader(new HTTPHeader("grant_type", "authorization_code"));
	     httpResponse = fetchService.fetch(httpRequest);
	     InputStream in=getContentAsStream(httpResponse);
		  BufferedReader reader = new BufferedReader( new InputStreamReader(in));
		  String line;
		  String output="";
		  while ((line = reader.readLine()) != null) {
			  output=output+line;
          }
          reader.close();
          return output;
		  }catch(Exception e){
			  e.printStackTrace();
			  System.out.println(e.getMessage());
			  return e.getMessage();
		  }
		  
	}
	public static byte[] getContentAsBytes(HTTPResponse httpResponse) {
	      return httpResponse.getContent();
	    }

	    public static InputStream  getContentAsStream(HTTPResponse httpResponse) {
	      return new ByteArrayInputStream(getContentAsBytes(httpResponse));
	    }
}