1.獲取HttpURLConnection實例，一般new出一個URL對象并且傳入目標網絡地址，再調用openConnection();
URL url = new URL("http://localhost:8080/TestHttpURLConnectionPro/index.jsp");
HttpURLConnection connection = (HttpURLConnection)url.openConnection();
2.設置Get/Post
connection.setRequestMethod("POST");
3.設置鏈接超時、讀取超時毫秒數，消息頭等
connection.setConnectTimeout(8000);
connection.setReadTimeout(8000);
4.getInputStream()獲取服務器返回的輸入流
InputStream in = connection.getInputStream();
5.關閉HTTP鏈接
connection.disConnect();
