public static String sendPost(String url, String param) {
      PrintWriter out = null;
      BufferedReader in = null;
      String result = "";
      try {
        URL realUrl = new URL(url);
        // 打开和URL之间的连接
        URLConnection conn = realUrl.openConnection();
        // 设置通用的请求属性
        conn.setRequestProperty("accept", "*/*");
        conn.setRequestProperty("connection", "Keep-Alive");
        conn.setRequestProperty("user-agent",
            "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
        conn.setConnectTimeout(4000);
        conn.setReadTimeout(4000);
        // 发送POST请求必须设置如下两行
        conn.setDoOutput(true);
        conn.setDoInput(true);
        // 获取URLConnection对象对应的输出流
        out = new PrintWriter(conn.getOutputStream());
        // 发送请求参数
        out.print(param);
        // flush输出流的缓冲
        out.flush();
        // 定义BufferedReader输入流来读取URL的响应
        in = new BufferedReader(
            new InputStreamReader(conn.getInputStream()));
        String line;
        while ((line = in.readLine()) != null) {
          result += line;
        }
      } catch (Exception e) {
        System.out.println("发送 POST 请求出现异常！");
        //e.printStackTrace();
      }
      //使用finally块来关闭输出流、输入流
      finally{
        try{
          if(out!=null){
            out.close();
          }
          if(in!=null){
            in.close();
          }
        }
        catch(IOException ex){
          //ex.printStackTrace();
        }
      }
      return result;
    }