LISTING 1

public class InvalidateCacheCommand implements Command {

	private final static Map GLOBAL_CACHE = new HashMap();

	private final String key;

	public InvalidateCacheCommand(String key) {
		if (key == null) {
			throw new IllegalArgumentException("Key is null.");
		}
		this.key = key;
	}

	public void execute() {
		System.out.println("Clearing cache for key: " + key);
		GLOBAL_CACHE.remove(key);
	}
}

LISTING 2

// NOTE: This class uses undocumented private WebLogic APIs not guaranteed to be supported
 by future versions of WebLogic. Use at your own risk.

public final class ClusterNotifier {

	private static MulticastSession session;

	private ClusterNotifier() {}

	public static void notify(Command command) {
		if (command == null) {
			throw new IllegalArgumentException("Command is null.");
		}

		if (session == null) {
		System.out.println("Not running in a cluster.  Invoking command locally..");
		command.execute();
		}
		else
		{
			System.out.println("Running in a cluster.  Sending message to cluster
			 members..");
			try
			{
				session.send(new DelegateMessage(command));
			} catch (IOException io) {
				io.printStackTrace();
				System.err.println("An IO Exception occurred while sending the " +
				 "message to the cluster." + io.getMessage());
			}
		}

	}

	public static void main(String argv[]) {
		Command command = new InvalidateCacheCommand("TestKey");
		ClusterNotifier.notify(command);
	}

	 private static synchronized MulticastSession getSession()
	 {
        if(session == null)
        {
            ClusterServices cluster = ClusterService.getServices();
            if(cluster == null)
                return null;
            session = cluster.createMulticastSession(null, -1, false);
        }
	    return session;
	  }

	public static class DelegateMessage implements GroupMessage {
		private final Command command;

		public DelegateMessage() {
			this(null);
		}

		public DelegateMessage(Command command) {
			this.command = command;
		}

		public void execute(HostID ignoredHostID) {
			if (command != null) {
				command.execute();
			}
		}
	}
}