Why can't I use any Ports with Java.net?

Question

I'm trying to make an online Chat but when I launch the code I always get java.net.BindException: Address already in use (Bind failed). I've tried changing the Port several times but I always get the same Exception. Sometimes the Code still executes and Everything works fine but the exception is still a problem for me. I know there are questions similar to mine but there are only solutions for windows users and I am a Mac user. Here's the code(It's not completely finished and the error occurs on the Server part @ new ServerSocket();)

public Server(Client c) {

    try {
        ServerSocket serverSocket = new ServerSocket(65531);
        while (true) {
            Socket s = serverSocket.accept();
            new Thread() {
                @Override
                public void run() {
                    super.run();

                    try {
                        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(s.getInputStream()));
                        String message = bufferedReader.readLine();
                        System.out.println("Antwort vom Client: " + message);
                        c.receivedMessage(message);
                        System.out.println("Adresse: "+s.getInetAddress().toString());
                        System.out.println(s.getInetAddress().getHostAddress());
                        s.close();
                    } catch (Exception e) {

                    }
                }
            }.run();


        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

EDIT:

I've checked the port before after and while the application was running and it is only used when running so the Server Socket is kinda working but I still get an exception

BTW, `new Thread().run()` is kind of pointless. Did you mean `.start()`? — glglgl, May 28 '19 at 08:21
I don't know. I'm new at Multithreading. this was just code I copied from a website. But changing it didn't solve it(It also worked with run. — Lukas Sokcevic, May 28 '19 at 08:22
Did you try to research what that exception is trying to tell you? — f1sh, May 28 '19 at 08:24
Yes, it means the Port is already being used but I checked with Nmap and there shouldn't be any service running on it — Lukas Sokcevic, May 28 '19 at 08:25
`nmap` is checking it from the outside on the network layer. You should check your processlist — f1sh, May 28 '19 at 08:27
@f1sh There are only solutions for windows user but I am a Mac user. I even tried to "translate it to Mac" but it still didn't work — Lukas Sokcevic, May 28 '19 at 09:06
There are solutions for Mac on that question, eg https://stackoverflow.com/a/15153736/466862 — Mark Rotteveel, May 28 '19 at 09:53
@MarkRotteveel I've already tried that and someone has commented it on my post but it didn't work — Lukas Sokcevic, May 28 '19 at 09:54

Matthew · Answer 1 · 2019-05-28T08:50:48.160

The exception java.net.BindException: Address already in use is trying to tell you that a Java application is trying to connect on a certain port but that port is already used by some other process and JVM Bind to that particular port.

You need to find out which process is already using that port and kill it before trying to connect to the socket. This is how you can do that:

Enter the following in cmd (as administrator):

netstat -ano | findstr :<yourPortNumber>

Then you execute this command after identify the PID:

taskkill /PID <typeyourPIDhere> /F

Run the first command again to make sure the process has been successfully terminated. You will get an empty line if the previous operation succeeded.

Read more: https://javarevisited.blogspot.com/2011/12/address-already-use-jvm-bind-exception.html#ixzz5pCppM2qn

EDIT: Here is how to kill the process on Mac:

netstat -vanp tcp | grep <port number>

If you are using macOS El Capitan or Centos 7 see this answer.

I ran this command and it gave me a long output but the exception is still there — Lukas Sokcevic, May 28 '19 at 08:56

Björn Böing · Answer 2 · 2019-05-28T08:28:52.913

0

Most likely the port is still in use because of a previous run of your program and you did not close the socket correctly. So after an error or incomplete run the socket is still open and therefore the port is used.

Maybe you want to read about try-with-resource or add a finally where you make sure to close your socket if it was created successfully.

Make sure to close all running java processes and/or simply restart your PC to free the port for sure. Then edit your code to handle the port closing correctly and try again.

edited May 28 '19 at 08:28

answered May 28 '19 at 08:27

Björn Böing

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The application might also still be running. It might even be a previous instance of this very application, still running in the background inside the IDE. – f1sh May 28 '19 at 08:28
I terminated the application but it still won't work – Lukas Sokcevic May 28 '19 at 08:48
What exactly wont work, are you still getting the same error? – Matthew May 28 '19 at 08:53
Still getting the same exception – Lukas Sokcevic May 28 '19 at 08:58

Why can't I use any Ports with Java.net?

2 Answers2