Intercepting SIGTERM

The 'proper' way to terminate a java process on unix is by sending SIGTERM, waiting a bit, and then sending SIGKILL. This gives java a chance to clean - using Runtime.getRuntime().getShutdownHook().

If you want to intercept this and do some early cleanup, before letting the others do theirs you need to use sun.misc.Signal - which can also be used to intercept other signals.

Things to do in a shutdownHook ? Flush the logs, finish important background processes and much more.

Code to intercept the signal:

oldSigTERM = Signal.handle(new Signal("TERM"),
                new SignalHandler() {
    public void handle(Signal signal) {
      System.err.println("Quit using SIGTERM hook");
      notificationHandler.prepareToQuit();
      if (oldSigTERM != null) {
        oldSigTERM.handle(signal);
      }
    }
  });