How to avoid java.net.BindException: Address already in use

Question

The following was running for 1 hour and then closed:

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); 
        }
      });
  }

When I re-run the same thing it fails with a 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)

It takes about 3 to 4 minutes before it will execute successfully again. How can I make it work immediately after shutting down?

Follow up:

$ 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)

Solution 1

You will see that your setReuseAddress(true) is being called too late i.e. after the bind throws an exception.

You can create an unbound ServerSocket, make it reusable and then bind it, in three steps.

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

Solution 2

I had a similar problem in one of my programs, but it ended up that I was just actually running an instance of the program from my IDE - which I hadn't noticed. Always double check there isn't something running in the background.

Comments

[Admin]

Thank you! I have tried according to your great advise. But i still could not fix it. Please see above my edit follow up section. There are still few showing ESTABLISHED but actually i have none and even my application is terminated. But i can still do telnet localhost thatport

[user207421]

@YumYumYum the presence of a port in the CLOSE_WAIT state indicates that the application was still running when you took that netstat.

[tobi42]

In my scenario I did not really care for the port number and could therefore use ServerSocket myServer = new ServerSocket(0); final int port = myServer.getLocalPort();

[Vishy]

@tobi42 in that case, you won't be reusing a port so it won't be a problem.