how to call a method once an endless thread is stopped manually

Question

I have an endless thread running in my code. This thread creates UDP read methods and listens on the connection endlessly.

What I want to do is to execute a piece of code once I stop the thread execution manually (by clicking the stop button in eclipse).

Is their a possible way of achieving this ?

While searching the same I came across a onDestroy() method but sadly that is applicable for Android Java only !!!

Answer 1

1. First of all, the right way to stop a network reading thread is to close the socket. Then read/receive method throws an exception and you catch it

   private final DatagramSocket udpSocket;
   private volatile boolean closed; // or AtomicBoolean
   ...
   
   public synchronized void start() throws IOException {
       if (closed) {
           throw new IOException("Closed");
       }
       new Thread(new Runnable() {
           @Override
           public void run() {
               final byte[] buffer = new byte[1024];
               final DatagramPacket dp = new DatagramPacket(buffer, buffer.length);
               Throwable error = null;
   
               try {
                   while(true) {            
                       udpSocket.receive(dp);
                       final String message = new String(buffer, 0, dp.getLength());
                       System.out.println(message);
                   }
               } catch (Throwable t) {
                   if (!closed) {
                       error = t;
                   }
               }
               if (error != null) {
                   // do some work for error
               }
           }
       }).start();
   }
   
   public void close() throws IOException {
       synchronized(this) {
           if (closed) return;
           closed = true;
       }
       udpSocket.close();
   }
   

2. When you click STOP button in an IDE, usually you terminate (abnormally)/kill immediately your JVM process. I'd suggest to run your process in console and use Ctrl+C to stop the process and add a ShutdownHook:

   public static void main(String[] args) {
       Runtime.getRuntime().addShutdownHook(
           new Thread(
               new Runnable() {
                   @Override
                   public void run() {
                       System.out.println("Shutdown");
                   }
               }));            
   }
   

or run it in Eclipse but stop with taskkill on Windows/kill on Linux from command line interface to close JVM process normally.

See details at http://www.oracle.com/technetwork/java/javase/signals-139944.html https://docs.oracle.com/javase/7/docs/api/java/lang/Runtime.html#addShutdownHook%28java.lang.Thread%29