Java tutorial
package org.apache.jcs.auxiliary.remote; /* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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. */ import java.io.IOException; import java.io.Serializable; import java.util.Collections; import java.util.Set; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.jcs.auxiliary.remote.behavior.IRemoteCacheService; import org.apache.jcs.engine.ZombieCacheService; import org.apache.jcs.engine.behavior.ICacheElement; import org.apache.jcs.utils.struct.BoundedQueue; import org.apache.jcs.utils.timing.ElapsedTimer; /** * Zombie adapter for the remote cache service. It just balks if there is no queue configured. If a * queue is configured, then events will be added to the queue. The idea is that when proper * operation is restored, the remote cache will walk the queue. The queue must be bounded so it does * not eat memory. * <p> * Much of this is potentially reusable. * <p> * TODO figure out a way to get the propagate method into an interface for Zombies. */ public class ZombieRemoteCacheService extends ZombieCacheService implements IRemoteCacheService { private final static Log log = LogFactory.getLog(ZombieRemoteCacheService.class); private int maxQueueSize = 0; private BoundedQueue queue; /** * Default. */ public ZombieRemoteCacheService() { queue = new BoundedQueue(0); } /** * Sets the maximum number of items that will be allowed on the queue. * <p> * @param maxQueueSize */ public ZombieRemoteCacheService(int maxQueueSize) { this.maxQueueSize = maxQueueSize; queue = new BoundedQueue(maxQueueSize); } /** * Gets the number of items on the queue. * <p> * @return size of the queue. */ public int getQueueSize() { return queue.size(); } /** * Adds an update event to the queue if the maxSize is greater than 0; * <p> * (non-Javadoc) * @see org.apache.jcs.auxiliary.remote.behavior.IRemoteCacheService#update(org.apache.jcs.engine.behavior.ICacheElement, * long) */ public void update(ICacheElement item, long listenerId) { if (maxQueueSize > 0) { PutEvent event = new PutEvent(item, listenerId); queue.add(event); } // Zombies have no inner life return; } /** * Adds a removeAll event to the queue if the maxSize is greater than 0; * <p> * (non-Javadoc) * @see org.apache.jcs.auxiliary.remote.behavior.IRemoteCacheService#remove(java.lang.String, * java.io.Serializable, long) */ public void remove(String cacheName, Serializable key, long listenerId) { if (maxQueueSize > 0) { RemoveEvent event = new RemoveEvent(cacheName, key, listenerId); queue.add(event); } // Zombies have no inner life return; } /** * Adds a removeAll event to the queue if the maxSize is greater than 0; * <p> * (non-Javadoc) * @see org.apache.jcs.auxiliary.remote.behavior.IRemoteCacheService#removeAll(java.lang.String, * long) */ public void removeAll(String cacheName, long listenerId) { if (maxQueueSize > 0) { RemoveAllEvent event = new RemoveAllEvent(cacheName, listenerId); queue.add(event); } // Zombies have no inner life return; } /** * Does nothing. Gets are synchronous and cannot be added to a queue. * <p> * (non-Javadoc) * @see org.apache.jcs.auxiliary.remote.behavior.IRemoteCacheService#get(java.lang.String, * java.io.Serializable, long) */ public ICacheElement get(String cacheName, Serializable key, long requesterId) throws IOException { // Zombies have no inner life return null; } /** * Does nothing. * <p> * (non-Javadoc) * @see org.apache.jcs.auxiliary.remote.behavior.IRemoteCacheService#getGroupKeys(java.lang.String, * java.lang.String) */ public Set getGroupKeys(String cacheName, String groupName) { return Collections.EMPTY_SET; } /** * Walk the queue, calling the service for each queue operation. * <p> * @param service * @throws Exception */ protected void propagateEvents(IRemoteCacheService service) throws Exception { int cnt = 0; if (log.isInfoEnabled()) { log.info("Propagating events to the new RemoteService."); } ElapsedTimer timer = new ElapsedTimer(); while (!queue.isEmpty()) { cnt++; // for each item, call the appropriate service method ZombieEvent event = (ZombieEvent) queue.take(); if (event instanceof PutEvent) { PutEvent putEvent = (PutEvent) event; service.update(putEvent.element, event.requesterId); } else if (event instanceof RemoveEvent) { RemoveEvent removeEvent = (RemoveEvent) event; service.remove(event.cacheName, removeEvent.key, event.requesterId); } else if (event instanceof RemoveAllEvent) { service.removeAll(event.cacheName, event.requesterId); } } if (log.isInfoEnabled()) { log.info("Propagated " + cnt + " events to the new RemoteService in " + timer.getElapsedTimeString()); } } /** * Base of the other events. */ private abstract class ZombieEvent { String cacheName; long requesterId; } /** * A basic put event. */ private class PutEvent extends ZombieEvent { ICacheElement element; /** * Set the element * @param element * @param requesterId */ public PutEvent(ICacheElement element, long requesterId) { this.requesterId = requesterId; this.element = element; } } /** * A basic Remove event. */ private class RemoveEvent extends ZombieEvent { Serializable key; /** * Set the element * @param cacheName * @param key * @param requesterId */ public RemoveEvent(String cacheName, Serializable key, long requesterId) { this.cacheName = cacheName; this.requesterId = requesterId; this.key = key; } } /** * A basic RemoveAll event. */ private class RemoveAllEvent extends ZombieEvent { /** * @param cacheName * @param requesterId */ public RemoveAllEvent(String cacheName, long requesterId) { this.cacheName = cacheName; this.requesterId = requesterId; } } }