Replacing jsvc for Java daemons

For some time I have been using the Apache Commons Daemon project to run and maintain my Java based services. jsvc did/does a reasonable job but I start to worry when a project has not been touched for a while.

In addition I am in the midst of deploying a Java based service on Mac OS X and so I am in the world of launchd. I wanted a better way of controlling Java based services; particularly one that did not fork multiple processes given launchd's garbage collection.

The principal issue with a Java service running in the background is that you need to have it respond asynchronously to various singals; particularly SIGTERM which of course is issued when the OS is being shutdown. My service needs to shut down gracefully.

Enter in a feature of Java 1.4.2 that I did not realise existed: Shutdown Hooks. In essence Shutdown Hooks provides your Java application an opportunity to respond to the application quitting.

Followers of this blog know that I am an Apache Camel addict. You will not therefore be surprised to find that what follows is an example of how to start up and shutdown a Camel context using Java's Shutdown Hooks.

public class EntryPoint {
  static Logger logger = 
    Logger.getLogger(EntryPoint.class.getName());

  static EntryPoint entryPoint;

  Main main;

  public static void main(String[] args) {
    entryPoint = new EntryPoint();

    Runtime.getRuntime()
     .addShutdownHook(new Thread() {
      public void run() {
        try {
          entryPoint.stop();
        } catch (Exception e) {
          logger.fatal(e.toString());
        }
      }
    });

    try {
      entryPoint.start();
    } catch (Exception e) {
      logger.fatal(e.toString());
    }

  }

  public void start() throws Exception {
    logger.info("Starting up");

    // Start up the context
    main = new Main();
    main.start();

    logger.info("Started");
  }

  public void stop() throws Exception {
    logger.info("Stopping");

    // Shutdown the context
    main.stop();

    logger.info("Stopped");
  }
}