An EventBus that persists the most recent event sent.

PersistingAsyncEventBus.java

package com.google.common.eventbus;

import com.google.common.collect.ClassToInstanceMap;
import com.google.common.collect.Multimap;
import com.google.common.collect.MutableClassToInstanceMap;
import roboguice.util.Ln;

import java.util.concurrent.Executor;

/**
 * An {@link EventBus} that persists the most recent event sent.
 *
 * This class has to be in this package because the EventBus isn't really meant for extension. It could potentially
 * stop working with the next Guava release. See
 * http://groups.google.com/group/guava-discuss/browse_thread/thread/80f97e66728fe4dc/cdf758d64f1cf50b
 */
public class PersistingAsyncEventBus extends AsyncEventBus {
    private final HandlerFindingStrategy myFinder = new AnnotatedHandlerFinder();
    private final ClassToInstanceMap<Object> sentEvents = MutableClassToInstanceMap.create();

    public PersistingAsyncEventBus(final String identifier, final Executor executor) {
        super(identifier, executor);
    }

    @Override
    public void post(final Object event) {
        super.post(event);
        sentEvents.put(event.getClass(), event);
    }

    @Override
    public void register(final Object object) {
        super.register(object);

        final Multimap<Class<?>,EventHandler> allHandlers = myFinder.findAllHandlers(object);

        for (Class<?> aClass : allHandlers.keySet()) {
            final Object event = sentEvents.getInstance(aClass);
            if(event != null) {
                for (EventHandler eventHandler : allHandlers.get(aClass)) {
                    Ln.i("Enqueing cached event %s to %s", event, eventHandler);
                    enqueueEvent(event, eventHandler);
                }
            }
        }

        dispatchQueuedEvents();
    }
}