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An abstract description of a simple message bus to be used within an application.
/*
* #%L
* *********************************************************************************************************************
*
* These Foolish Things - Miscellaneous utilities
* http://thesefoolishthings.tidalwave.it - git clone git@bitbucket.org:tidalwave/thesefoolishthings-src.git
* %%
* Copyright (C) 2009 - 2016 Tidalwave s.a.s. (http://tidalwave.it)
* %%
* *********************************************************************************************************************
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
* an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
* specific language governing permissions and limitations under the License.
*
* *********************************************************************************************************************
*
* $Id$
*
* *********************************************************************************************************************
* #L%
*/
package it.tidalwave.messagebus.spi;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.ThreadSafe;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import it.tidalwave.messagebus.MessageBus;
import it.tidalwave.messagebus.MessageBus.Listener;
import lombok.Getter;
import lombok.extern.slf4j.Slf4j;
/***********************************************************************************************************************
*
* A partial implementation of {@link MessageBus}.
*
* @author Fabrizio Giudici
* @version $Id$
*
**********************************************************************************************************************/
@ThreadSafe @Slf4j
public class SimpleMessageBus implements MessageBus
{
private final Map, List>>> listenersMapByTopic = new HashMap<>();
private final MessageDelivery messageDelivery;
@Getter
private final Executor executor;
/*******************************************************************************************************************
*
*
*
******************************************************************************************************************/
public SimpleMessageBus()
{
this(Executors.newFixedThreadPool(10));
}
/*******************************************************************************************************************
*
*
*
******************************************************************************************************************/
public SimpleMessageBus (final @Nonnull Executor executor)
{
this(executor, new SimpleAsyncMessageDelivery());
}
/*******************************************************************************************************************
*
*
*
******************************************************************************************************************/
public SimpleMessageBus (final @Nonnull Executor executor, final @Nonnull MessageDelivery messageDelivery)
{
this.executor = executor;
this.messageDelivery = messageDelivery;
this.messageDelivery.initialize(this);
log.info("MessageBusSupport configured with {}", messageDelivery);
}
/*******************************************************************************************************************
*
* {@inheritDoc}
*
******************************************************************************************************************/
@Override
public void publish (final @Nonnull Topic message)
{
publish((Class)message.getClass(), message);
}
/*******************************************************************************************************************
*
* {@inheritDoc}
*
******************************************************************************************************************/
@Override
public void publish (final @Nonnull Class topic, final @Nonnull Topic message)
{
log.trace("publish({}, {})", topic, message);
messageDelivery.deliverMessage(topic, message);
}
/*******************************************************************************************************************
*
* {@inheritDoc}
*
******************************************************************************************************************/
@Override
public void subscribe (final @Nonnull Class topic, final @Nonnull Listener listener)
{
log.debug("subscribe({}, {})", topic, listener);
findListenersByTopic(topic).add(new WeakReference<>(listener));
}
/*******************************************************************************************************************
*
* {@inheritDoc}
*
******************************************************************************************************************/
@Override
public void unsubscribe (final @Nonnull Listener listener)
{
log.debug("unsubscribe({})", listener);
for (final List>> list : listenersMapByTopic.values())
{
for (final Iterator>> i = list.iterator(); i.hasNext(); )
{
final WeakReference ref = i.next();
if ((ref.get() == null) || (ref.get() == listener))
{
i.remove();
}
}
}
}
/*******************************************************************************************************************
*
*
******************************************************************************************************************/
protected void dispatchMessage (final @Nonnull Class topic, final @Nonnull TOPIC message)
{
final HashSet, List>>>> clone =
new HashSet<>(listenersMapByTopic.entrySet());
for (final Map.Entry, List>>> e : clone)
{
if (e.getKey().isAssignableFrom(topic))
{
final List>> listeners = (List)e.getValue();
for (final WeakReference> listenerReference : listeners)
{
final MessageBus.Listener listener = listenerReference.get();
if (listener != null)
{
try
{
listener.notify(message);
}
catch (Throwable t)
{
log.warn("deliverMessage()", t);
}
}
}
}
}
}
/*******************************************************************************************************************
*
*
******************************************************************************************************************/
@Nonnull
private List>> findListenersByTopic (final @Nonnull Class topic)
{
final List tmp = listenersMapByTopic.get(topic);
List>> listeners = tmp;
if (listeners == null)
{
listeners = new ArrayList<>();
listenersMapByTopic.put(topic, (List)listeners);
}
return listeners;
}
}