url是對方系統URL，param是json字串

方法體：

private String sendPost(String url, String param) {
        PrintWriter out = null;
        BufferedReader in = null;
        String result = "";
        try {
            // 開啟和URL之間的連線
            HttpURLConnection conn = (HttpURLConnection)new URL(url).openConnection();
            // 設定通用的請求屬性
            conn.setRequestMethod("POST");
			conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");
            // 傳送POST請求必須設定如下兩行
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 獲取URLConnection物件對應的輸出流
            out = new PrintWriter(conn.getOutputStream());
            // 傳送請求引數
            out.print(param);
            // flush輸出流的緩衝
            out.flush();
            // 定義BufferedReader輸入流來讀取URL的響應
            in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("傳送 POST 請求出現異常！"+e);
            e.printStackTrace();
        }
        //使用finally塊來關閉輸出流、輸入流
        finally{
            try{
                if(out!=null){
                    out.close();
                }
                if(in!=null){
                    in.close();
                }
            }
            catch(IOException ex){
                ex.printStackTrace();
            }
        }
        return result;
    }