在URL.openconnection()时做了什么？

Question

我想知道在URL.openconnection()时做了什么.
我做了一些像这样的测试:

public static void main(String[] args) {
    //    testConnection("http://www.google.com");
    testConnection("http://219.09.34.23.1");
}

private static void testConnection(final String _url) {
    new Thread(new Runnable() {
        String strurl = _url;
        long starttime = 0;
        long endtime = 0;

        public void run() {
            try {
                System.out.println("open:" + strurl);

                starttime = System.currentTimeMillis();
                System.out.println("starttime:" + starttime);

                URL url = new URL(strurl);
                HttpURLConnection conn = (HttpURLConnection) url
                        .openConnection();

                endtime = System.currentTimeMillis();
                System.out.println("openConnection endtime:" + endtime);
                System.out
                        .println("spend:" + (endtime - starttime) + " ms");

                conn.connect();
                endtime = System.currentTimeMillis();
                System.out.println("connect endtime2:" + endtime);
                System.out
                        .println("spend:" + (endtime - starttime) + " ms");

                conn.getResponseCode();
                endtime = System.currentTimeMillis();
                System.out.println("endtime3:" + endtime);
                System.out
                        .println("spend:" + (endtime - starttime) + " ms");
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();

                endtime = System.currentTimeMillis();
                System.out.println("MalformedURLException endtime:"
                        + endtime);
                System.out
                        .println("spend:" + (endtime - starttime) + " ms");
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();

                endtime = System.currentTimeMillis();
                System.out.println(" IOException endtime:" + endtime);
                System.out
                        .println("spend:" + (endtime - starttime) + " ms");
            }

        }
    }).start();
}

当我运行testConnection("http://www.google.com")时,一切正常.
当我运行testConnection("http://219.09.34.23.1"),"219.09.34.23.1"是一个随机的ip可能不存在我写的,它打印这个:

open:http://219.09.34.23.1
starttime:1338978920350
openconnection endtime:1338978920355
spend:5 ms

    java.net.UnknownHostException: 219.09.34.23.1  
    at java.net.PlainSocketImpl.connect(Unknown Source)  
    at java.net.SocksSocketImpl.connect(Unknown Source)  
    at java.net.Socket.connect(Unknown Source)  
    at java.net.Socket.connect(Unknown Source)  
    at sun.net.NetworkClient.doConnect(Unknown Source)  
    at sun.net.www.http.HttpClient.openServer(Unknown Source)  
    at sun.net.www.http.HttpClient.openServer(Unknown Source)  
    at sun.net.www.http.HttpClient.<init>(Unknown Source)  
    at sun.net.www.http.HttpClient.New(Unknown Source)  
    at sun.net.www.http.HttpClient.New(Unknown Source)  
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(Unknown Source)  
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)  
    at sun.net.www.protocol.http.HttpURLConnection.connect(Unknown Source)  
    at Main$1.run(Main.java:37)  
    at java.lang.Thread.run(Unknown Source)

IOException endtime:1338978920393
spend:43 ms

这意味着花了5ms来运行openconnection,花了43ms来发现它是一个未知的主机,我的问题是,当URL.openconnection()为"219.09.34.23.1"是未知主机时,做了什么？谢谢你的帮助!

Answer 1

如果你读了URL.openConnection()的javadocs,你会发现:

返回一个URLConnection实例,该实例表示与URL引用的远程对象的连接.

每次调用此URL的协议处理程序的URLStreamHandler.openConnection(URL)方法时,都会创建一个新的URLConnection实例.

应该注意,URLConnection实例在创建时不建立实际的网络连接.只有在调用URLConnection.connect()时才会发生这种情况.

更新

您在"随机ip"中使用的IP无效; 它应该由4个八位字节组成,而不是5个.这43ms可能用于:(1)在非IP ip上进行DNS查找(2)打印堆栈跟踪.

Answer 2

打开连接不像连接

openconnection不允许你下载肯定的网址内容.你必须打电话给连接.但不是真的:)以下将解释:

您并不总是需要显式调用connect方法来启动连接.依赖于连接的操作(如getInputStream,getOutputStream等)将在必要时隐式执行连接.