java发送Http请求

/**
     * 发送主要方法,异常捕获
     * 
     * @param post
     * @param code
     * @return
*/
public static String doHttpRequest(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();
            HttpURLConnection connection = (HttpURLConnection)realUrl.openConnection();

            connection.addRequestProperty("Content-Type", "application/json;charset=UTF-8");
            connection.addRequestProperty("User-Agent", "mytest");
            connection.setConnectTimeout(60000);
            connection.setReadTimeout(60000);
            connection.setRequestMethod("POST");
            connection.setDoOutput(true);
            connection.getOutputStream().write(param.getBytes("utf8"));

// connection.setRequestProperty("Content-Type", "application/json");
int status = connection.getResponseCode();

            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(), "utf-8"));
            StringBuffer message = new StringBuffer();
while (reader.ready()) {
              message.append(reader.readLine());
            }
            reader.close();
            connection.connect();
if (status == 200) {
return  message.toString();
            }

        } catch (Exception e) {
            System.out.println("发送 POST 请求出现异常！"+e);
            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;

    }

记：

①  connection.addRequestProperty("Content-Type", "application/json;charset=UTF-8");如果是json数据这一个属性不添加，会让接收方收不到数据。
② 如果json数据以map<"String, object"> 的形式组装，当key对应得value为null的时候，会报错，如果以jsonobject.getbytes()以流的形式返回就不会出现这种问题。