URLConnection分析

// url是一個http地址
URL url = new URL("http://127.0.0.1:8080/index.jsp");
URLConnection urlConnection = url.openConnection();
HttpURLConnection httpURLConnection = (HttpURLConnection)urlConnection;
// 底層的正在實現類
System.out.println("httpURLConnection: " + httpURLConnection);
// 真正獲取獲取鏈接
httpURLConnection.connect();