使用java代码获取新浪微博应用的access token

package test;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URISyntaxException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.params.ConnRoutePNames;
import org.apache.http.impl.client.DefaultHttpClient;
public class WeiboAccessTokenRequest 
{
  static public void main(String[] arg)
  {
    //System.setProperty("http.proxyHost", "proxy.wdf.diablo.corp");
    //System.setProperty("http.proxyPort", "8080");
    HttpClient httpclient = new DefaultHttpClient();   
    HttpPost post = new HttpPost();
    URI url;
    try 
    {
      //url = new URI("https://api.weibo.com/oauth2/access_token");
      String request = "https://api.weibo.com/oauth2/access_token?client_id=3921363495&client_secret=bac53e1f9c1e66514cf7410e39d581dd"
          + "&grant_type=authorization_code&code=7420036e360713bab82f62a5275aaba7&redirect_uri=https://api.weibo.com/oauth2/default.html";
      url = new URI(request);
      post.setURI(url);
      HttpHost proxy = new HttpHost("proxy", 8080);
      httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);
      /*post.addHeader("client_id", "3921363495");
      post.addHeader("client_secret", "bac53e1f9c1e66514cf7410e39d581dd");
      post.addHeader("grant_type", "authorization_code");
      post.addHeader("code", "7420036e360713bab82f62a5275aaba7");
      post.addHeader("redirect_uri", "https://api.weibo.com/oauth2/default.html");*/
      HttpResponse response = httpclient.execute(post);
      HttpEntity entity = response.getEntity();     
      if (entity == null)
      {
        System.out.println("response is null!");
        return;
      }     
      InputStream instreams = entity.getContent();     
      String str = convertStreamToString(instreams);   
      System.out.println("Do something");    
      System.out.println(str);   
    } 
    catch (Exception e) 
    {
      e.printStackTrace();
    }
  }
  public static String convertStreamToString(InputStream is) 
  {       
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));       
    StringBuilder sb = new StringBuilder();       
    String line = null;       
    try {       
      while ((line = reader.readLine()) != null) {   
        sb.append(line + "\n");       
        }       
    } catch (IOException e) {       
      e.printStackTrace();       
    } finally {       
      try {       
        is.close();       
      } catch (IOException e) {       
        e.printStackTrace();       
      }       
    }       
    return sb.toString();       
  }   
}