微信获取unionid

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/**
 * 通过openid获取Unionid
 * @return
 */
public String getUnionidByOpenid(String openid) {
   try {
      String token_url = "https://api.weixin.qq.com/cgi-bin/user/info";
      String params = "access_token=" + accesstoken + "&openid=" +openid+ "&lang=zh_CN";
      String result = sendGet(token_url, params);
      System.out.println("getUnionidByOpenid:"+result);
      JSONObject json = new JSONObject(result);
      if (json.has("unionid")) {
         return json.get("unionid").toString();
      } else {
         return null;
      }
   } catch (Exception e) {
      error(e);
   }
   return null;
}

/**
 * 向指定URL发送GET方法的请求
 *
 * @param url
 *            发送请求的URL
 * @param param
 *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
 * @return URL 所代表远程资源的响应结果
 */
public  String sendGet(String url, String param) {
   String result = "";
   BufferedReader in = null;
   try {
      String urlNameString = url + "?" + param;
      URL realUrl = new URL(urlNameString);
      // 打开和URL之间的连接
      URLConnection connection = realUrl.openConnection();
      // 设置通用的请求属性
      connection.setRequestProperty("accept", "*/*");
      connection.setRequestProperty("connection", "Keep-Alive");
      connection.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
      // 建立实际的连接
      connection.connect();
      // 定义 BufferedReader输入流来读取URL的响应
      in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
      String line;
      while ((line = in.readLine()) != null) {
         result += line;
      }
   } catch (Exception e) {
      e.printStackTrace();
   } finally {
      try {
         if (in != null) {
            in.close();
         }
      } catch (Exception e2) {
         e2.printStackTrace();
      }
   }
   return result;
}