Java tutorial
/* This file is part of Subsonic. Subsonic is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Subsonic is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Subsonic. If not, see <http://www.gnu.org/licenses/>. Copyright 2009 (C) Sindre Mehus */ package net.sourceforge.subsonic.ajax; import net.sourceforge.subsonic.Logger; import net.sourceforge.subsonic.service.SecurityService; import net.sourceforge.subsonic.util.BoundedList; import org.apache.commons.lang.StringUtils; import org.directwebremoting.WebContext; import org.directwebremoting.WebContextFactory; import javax.servlet.http.HttpServletRequest; import java.io.Serializable; import java.util.ArrayList; import java.util.Date; import java.util.Iterator; import java.util.LinkedList; import java.util.List; import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; /** * Provides AJAX-enabled services for the chatting. * This class is used by the DWR framework (http://getahead.ltd.uk/dwr/). * * @author Sindre Mehus */ public class ChatService { private static final Logger LOG = Logger.getLogger(ChatService.class); private static final String CACHE_KEY = "1"; private static final int MAX_MESSAGES = 10; private static final long TTL_MILLIS = 3L * 24L * 60L * 60L * 1000L; // 3 days. private final LinkedList<Message> messages = new BoundedList<Message>(MAX_MESSAGES); private SecurityService securityService; private long revision = System.identityHashCode(this); /** * Invoked by Spring. */ public void init() { // Delete old messages every hour. ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor(); Runnable runnable = new Runnable() { public void run() { removeOldMessages(); } }; executor.scheduleWithFixedDelay(runnable, 0L, 3600L, TimeUnit.SECONDS); } private synchronized void removeOldMessages() { long now = System.currentTimeMillis(); for (Iterator<Message> iterator = messages.iterator(); iterator.hasNext();) { Message message = iterator.next(); if (now - message.getDate().getTime() > TTL_MILLIS) { iterator.remove(); revision++; } } } public synchronized void addMessage(String message) { WebContext webContext = WebContextFactory.get(); doAddMessage(message, webContext.getHttpServletRequest()); } public synchronized void doAddMessage(String message, HttpServletRequest request) { String user = securityService.getCurrentUsername(request); message = StringUtils.trimToNull(message); if (message != null && user != null) { messages.addFirst(new Message(message, user, new Date())); revision++; } } public synchronized void clearMessages() { messages.clear(); revision++; } /** * Returns all messages, but only if the given revision is different from the * current revision. */ public synchronized Messages getMessages(long revision) { if (this.revision != revision) { return new Messages(new ArrayList<Message>(messages), this.revision); } return null; } public void setSecurityService(SecurityService securityService) { this.securityService = securityService; } public static class Messages implements Serializable { private static final long serialVersionUID = -752602719879818165L; private final List<Message> messages; private final long revision; public Messages(List<Message> messages, long revision) { this.messages = messages; this.revision = revision; } public List<Message> getMessages() { return messages; } public long getRevision() { return revision; } } public static class Message implements Serializable { private static final long serialVersionUID = -1907101191518133712L; private final String content; private final String username; private final Date date; public Message(String content, String username, Date date) { this.content = content; this.username = username; this.date = date; } public String getContent() { return content; } public String getUsername() { return username; } public Date getDate() { return date; } } }