如何避免java.net.BindException：地址已在使用中

Question

以下代码运行了1个小时，然后关闭：

public class Mp extends JWindow implements MouseListener, MouseMotionListener {
    public static Mp j;
  private int serverPort = 0;
  private ServerSocket serverSock = null;
  private Socket sock = null;

  public static void main(final String[] args) throws IOException, InterruptedException, Exception {
    j = new Mp();
    j.setVisible(true);
    j.waitForConnections();
  }

  public void waitForConnections() {
    while (true) {
      try {
        sock = serverSock.accept();
        System.out.println("[TCPMediaHandler]: Accepted new socket");
        TCPMediaHandler handler = new TCPMediaHandler(sock);
        handler.start();
      } catch (IOException e) {
        e.printStackTrace(System.err);
      }
    }
  }

  public Mp() throws IOException {
    this.serverPort = 38891;
    serverSock = new ServerSocket(serverPort);
    serverSock.setReuseAddress(true);
    //serverSock.setSoTimeout(500);
    //serverSock.setSoLinger(true, 0);
    System.out.println("[TCPMediaHandler]: Server started");      
        this.v1.setBackground(Color.BLACK);
    this.v1.addMouseListener(this);
    /* Close the window */
    this.addWindowListener(new WindowAdapter() {
        public void windowClosing(WindowEvent we) {
          System.exit(0); 
        }
      });
  }

当我重新运行同一件事时，它失败了java.net.BindException：

$ java -cp /var/tmp/dist/Mp.jar test.Mp
Exception in thread "main" java.net.BindException: Address already in use
    at java.net.PlainSocketImpl.socketBind(Native Method)
    at java.net.AbstractPlainSocketImpl.bind(AbstractPlainSocketImpl.java:353)
    at java.net.ServerSocket.bind(ServerSocket.java:336)
    at java.net.ServerSocket.<init>(ServerSocket.java:202)
    at java.net.ServerSocket.<init>(ServerSocket.java:114)
    at test.Mp.<init>(Mp.java)
    at test.Mp.main(Mp.java)

大约需要3至4分钟才能再次成功执行。关闭后如何使它立即工作？

跟进：

$ netstat | grep 38891
tcp       35      0 localhost:38891         localhost:37842         CLOSE_WAIT 
tcp        0      0 localhost:34955         localhost:38891         ESTABLISHED
tcp       32      0 localhost:38891         localhost:37824         CLOSE_WAIT 
tcp        0      0 localhost:38891         localhost:34955         ESTABLISHED

$ lsof -w -n -i tcp:38891
COMMAND    PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
xdg-scree 5254  sun   29u  IPv4 231948      0t0  TCP *:38891 (LISTEN)
xdg-scree 5355  sun   29u  IPv4 231948      0t0  TCP *:38891 (LISTEN)
xdg-scree 5455  sun   29u  IPv4 231948      0t0  TCP *:38891 (LISTEN)
telnet    7058  sun    3u  IPv4 242987      0t0  TCP 127.0.0.1:34955->127.0.0.1:38891 (ESTABLISHED)
sleep     9002  sun   29u  IPv4 231948      0t0  TCP *:38891 (LISTEN)
sleep     9005  sun   29u  IPv4 231948      0t0  TCP *:38891 (LISTEN)
sleep     9008  sun   29u  IPv4 231948      0t0  TCP *:38891 (LISTEN)

Answer 1

您会看到setReuseAddress（true）的调用为时已晚，即在绑定引发异常之后。

您可以通过三个步骤创建一个未绑定的ServerSocket，使其可重用，然后将其绑定。

ServerSocket ss = new ServerSocket();
ss.setReuseAddress(true);
ss.bind(new InetSocketAddress(12345));