为什么是java。网SocketException:socket在java之后关闭。网ConnectException:连接被拒绝'？

Question

我正在尝试连接到一个远程主机，一遍又一遍地等待它出现。然而，在一次连接被拒绝的异常之后（因为服务器还没有运行），它会持续抛出socket关闭异常。为什么插座会被关闭？socket应该与调用失败的connect（）之前处于相同的状态，不是吗

                while(!tcpSock.isConnected()) {
                    try {
                        tcpSock.connect(destination);
                    } catch (SocketException e) {
                        System.err.println(e.toString());
                    }
                }

导致

Setting TCP client mode connecting to remote host localhost/127.0.0.1 port 4500
java.net.ConnectException: Connection refused: connect
java.net.SocketException: Socket closed
java.net.SocketException: Socket closed
java.net.SocketException: Socket closed
java.net.SocketException: Socket closed

期望的行为是

Setting TCP client mode connecting to remote host localhost/127.0.0.1 port 4500
java.net.ConnectException: Connection refused: connect
java.net.ConnectException: Connection refused: connect
java.net.ConnectException: Connection refused: connect
java.net.ConnectException: Connection refused: connect
Established connection to: localhost port 4500

（调试完成后，我将注释掉异常的打印内容。）

Answer 1

看看OpenJDK源代码。。。当connect(...)调用失败时，SocketImpl代码调用Socket上的close()

这是Java 11中的代码（在java.net.AbstractPlainSocketImpl）：

protected void connect(String host, int port)
    throws UnknownHostException, IOException
{
    boolean connected = false;
    try {
        InetAddress address = InetAddress.getByName(host);
        this.port = port;
        this.address = address;

        connectToAddress(address, port, timeout);
        connected = true;
    } finally {
        if (!connected) {
            try {
                close();  // <<   HERE
            } catch (IOException ioe) {
                /* Do nothing. If connect threw an exception then
                   it will be passed up the call stack */
            }
        }
    }
}

对SocketImpl对象的close()调用会导致Socket被标记为关闭

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简而言之，Java Socket对象不支持在连接尝试失败后重试。如果要重试，代码需要创建一个新的Socket对象

关于Socket这样做是否正确的讨论是无关紧要的。只是。。。而且这种情况极不可能改变。唯一可能改变的是，他们可能会在Socketjavadocs中记录这种行为