How to Interrupt a Serversocket Accept() Method

How can I interrupt a ServerSocket accept() method?

You can call close() from another thread, and the accept() call will throw a SocketException.

Stopping a ServerSocket accept() loop thread

I would just do

public void stop() {
    running = false;
    try{
        if (server != null) server.close ();
    } catch (IOException ignored){
    }
}

It doesn't appear you even need the running flag. However I would use it in your server accept code to determine if an Exception is expected or not. i.e. when running == false ignore all exceptions.

I would make running volatile.

I would make start()/stop() synchronized if you can run these from different threads.

Java Server Socket Interrupt How to

Here's an example how to close a socket from other thread:

private static volatile ServerSocket serverSocket;

public static void main(String[] args) throws InterruptedException, IOException {
    Thread serverThread = new Thread(new ServerThread());
    serverThread.start();
    Thread.sleep(1000); // wait a  bit, then close
    serverSocket.close();
}

static class ServerThread implements Runnable {

    private BufferedReader input;

    public void run() {
        try {
            serverSocket = new ServerSocket(25);
            while (true) {
                Socket socket = serverSocket.accept();
                // client request handling logic
            }

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

    }
}

How to interrupt a thread if it is to open socket?

ServerSocket.accept() is a blocking call that is not responsive to thread interruption. Almost all the java.net blocking calls (connect, read, accept, etc) do not respond to Thread.interrupt(). This behavior is "as designed".

A way to wake up a thread blocked in .accept() or .read() is to close the underlying socket.

Alternatively you could set SO_TIMEOUT (setSoTimeout) on the ServerSocket, which will cause .accept() to wake up periodically by throwing a SocketTimeoutException. You could catch that exception and use it as an opportunity to check the interrupt status on the thread.

The java.nio package (Java 1.4+) provides an alternate sockets API that is more responsive to interruption.

Java: interrupt accept method without close the server socket

You can set server socket timeout with setSoTimeout.
Once expired a SocketTimeoutException is raised.

Interrupting accept()

The solution here is to not call accept when there's nothing to do. Just use non-blocking select or poll to wait until there's something to accept, then accept at that point. Unless you create a really tiny timeout there won't be any performance implications of waking up from the non-blocking call and going back to wait on that socket again.

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