原文地址:https://www.cnblogs.com/momo1210/p/6283578.html
DWR 工作原理:
是通过动态把 Java 类生成为 Javascript。它的代码就像 Ajax 一样,你感觉调用就像发生在浏览器端,但是实际上代码调用发生在服务器端,DWR 负责数据的传递和转换。这种从 Java 到JavaScript的远程调用功能的方式使DWR用起来有种非常像RMI或者SOAP的常规RPC机制,而且DWR的优点在于不需要任何的网页浏览器插件就能运行在网页上。
Java 从根本上讲是同步机制,然而 AJAX 却是异步的。所以你调用远程方法时,当数据已经从网络上返回的时候,你需要提供有反调 (callback) 功能的 DWR,即你的js代码调用最后一个参数是一个回调函数,由回调函数处理数据返回后想做的操作。
Comet
Comet方式通俗的说就是一种长连接机制(long lived http)。同样是由Browser端主动发起请求,但是Server端以一种似乎非常慢的响应方式给出回答。这样在这个期间内,服务器端可以使用同一个connection把要更新的数据主动发送给Browser。因此请求可能等待较长的时间,期间没有任何数据返回,但是一旦有了新的数据,它将立即被发送到客户机。Comet又有很多种实现方式,但是总的来说对Server端的负载都会有增加.虽然对于单位操作来说,每次只需要建议一次connection,但是由于connection是保持较长时间的,对于 server端的资源的占用要有所增加。
优点: 实时性好(消息延时小);性能好(能支持大量用户)
缺点: 长期占用连接,丧失了无状态高并发的特点。
应用: 股票系统、实时通讯。
1.先配置web.xml
<!-- dwr start --> <servlet> <!-- dwr框架的核心控制器 --> <servlet-name>dwr-invoker</servlet-name> <servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class> <!-- 在服务器端启用反向ajax --> <init-param> <param-name>activeReverseAjaxEnabled</param-name> <param-value>true</param-value> </init-param> <!-- 为了得到更详细的调试信息 --> <init-param> <param-name>debug</param-name> <param-value>true</param-value> </init-param> <init-param> <param-name>crossDomainSessionSecurity</param-name> <param-value>false</param-value> </init-param> <init-param> <param-name>allowScriptTagRemoting</param-name> <param-value>true</param-value> </init-param> <init-param> <param-name>org.directwebremoting.extend.ScriptSessionManager </param-name> <param-value>com.worklite.core.tools.dwr.DWRScriptSessionManager</param-value> </init-param> <!-- 在服务器启动阶段,该servlet实例被创建 --> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>dwr-invoker</servlet-name> <!-- 发送如下的请求,都会交给dwr的核心控制器处理 --> <url-pattern>/dwr/*</url-pattern> </servlet-mapping> <!-- dwr end -->
2.新建dwr.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN" "http://getahead.org/dwr/dwr30.dtd"> <dwr> <allow> <create creator="new" javascript="DwrPush"> <param name="class" value="com.worklite.core.tools.dwr.DwrPush"/> </create> <create creator="new" javascript="ClientInitUtil"> <param name="class" value="com.worklite.core.tools.dwr.ClientInitUtil"/> </create> <create creator="new" javascript="WebMultiplePushUtil"> <param name="class" value="com.worklite.core.tools.dwr.WebMultiplePushUtil"/> </create> <create creator="new" javascript="WebSinglePushUtil"> <param name="class" value="com.worklite.core.tools.dwr.WebSinglePushUtil"/> </create> <create creator="new" javascript="WebSingleGamePushUtil"> <param name="class" value="com.worklite.core.tools.dwr.WebSingleGamePushUtil"/> </create> </allow> </dwr>
3.编写后台需要的类。
(1)DWRScriptSessionListener
public class DWRScriptSessionListener implements ScriptSessionListener { //维护一个Map key为session的Id, value为ScriptSession对象 public static final Map<String, ScriptSession> scriptSessionMap = new MirrorMap<String, ScriptSession>(); /** * ScriptSession创建事件 */ @Override public void sessionCreated(ScriptSessionEvent event) { WebContext webContext = WebContextFactory. get(); HttpSession session = webContext.getSession(); ScriptSession scriptSession = event.getSession(); scriptSessionMap.put(session.getId(), scriptSession); //添加scriptSession } /** * ScriptSession销毁事件 */ @Override public void sessionDestroyed(ScriptSessionEvent event) { //WebContext webContext = WebContextFactory. get(); //HttpSession session = webContext.getSession(); //scriptSessionMap.remove(session.getId()); //移除scriptSession } /** * 获取所有ScriptSession */ public static Collection<ScriptSession> getScriptSessions(){ return scriptSessionMap.values(); } public static ScriptSession getScriptSession(String str){ Collection<ScriptSession> sessions = DWRScriptSessionListener.getScriptSessions(); //遍历每一个ScriptSession for (ScriptSession scriptSession : sessions){ String tag = (String)scriptSession.getAttribute(str); if ( tag!=null&&str.equals(tag)) { return scriptSession; } } return null; } public static int Count(String wId){ Collection<ScriptSession> sessions = DWRScriptSessionListener.getScriptSessions(); //遍历每一个ScriptSession int i=0; for (ScriptSession scriptSession : sessions){ String tag = (String)scriptSession.getAttribute(wId); if ( tag!=null&&wId.equals(tag)) { i++; } } return i; } public static boolean getCustomList(String wId,int customId){ Collection<ScriptSession> sessions = DWRScriptSessionListener.getScriptSessions(); //遍历每一个ScriptSession for (ScriptSession scriptSession : sessions){ String tagId=customId+wId; String tag = (String)scriptSession.getAttribute(tagId); if(tag!=null&&tagId.equals(tag)){ return true; } } return false; } public static List<String> getCustomList(String wId){ List<String> customList=new ArrayList<String>(); Collection<ScriptSession> sessions = DWRScriptSessionListener.getScriptSessions(); //遍历每一个ScriptSession for (ScriptSession scriptSession : sessions){ Iterator<String> iter = scriptSession.getAttributeNames(); while(iter.hasNext()){ String str=iter.next(); if(str!=null&&str.contains(String.valueOf(","+wId))){ String customId = str.split(",")[0]; if (!customList.contains(customId)) customList.add(customId); } } } return customList; } public void init() throws ServletException { Container container = ServerContextFactory.get().getContainer(); ScriptSessionManager manager = container.getBean(ScriptSessionManager.class); ScriptSessionListener listener = new ScriptSessionListener() { public void sessionCreated(ScriptSessionEvent ev) { WebContext webContext = WebContextFactory. get(); HttpSession session = webContext.getSession(); ScriptSession scriptSession = ev.getSession(); scriptSessionMap.put(session.getId(), scriptSession); //添加scriptSession } public void sessionDestroyed(ScriptSessionEvent ev) { WebContext webContext = WebContextFactory. get(); HttpSession session = webContext.getSession(); ScriptSession scriptSession = scriptSessionMap.remove(session.getId()); //移除scriptSession } }; manager.addScriptSessionListener(listener); } }
(2)DWRScriptSessionManager
public class DWRScriptSessionManager extends DefaultScriptSessionManager { public DWRScriptSessionManager(){ //绑定一个ScriptSession增加销毁事件的监听器 this.addScriptSessionListener( new DWRScriptSessionListener()); Log.debug( "bind DWRScriptSessionListener"); } }
(3)DwrPush注册scriptSession
public class DwrPush { public void onPageLoad(final String tag){ //获取当前的ScriptSession ScriptSession scriptSession = WebContextFactory.get().getScriptSession(); scriptSession.setAttribute( tag, tag); } }
(4)WebMultiplePushUtil 用于群发
public class WebMultiplePushUtil { public void push(final String wId,final String content,final String command){ //过滤器 ScriptSessionFilter filter = new ScriptSessionFilter() { public boolean match(ScriptSession scriptSession) { String tag = (String)scriptSession.getAttribute(wId); if ( tag== null) { return false; } else { return wId.equals(tag); } } }; Runnable run = new Runnable(){ private ScriptBuffer script = new ScriptBuffer(); public void run() { //设置要调用的 js及参数 script.appendCall( "showMessage","{\"wId\":\""+wId+"\",\"content\":\""+content+"\",\"command\":\""+command+"\"}"); //得到所有ScriptSession Collection<ScriptSession> sessions = Browser.getTargetSessions(); //遍历每一个ScriptSession for (ScriptSession scriptSession : sessions){ scriptSession.addScript( script); } } }; //执行推送 Browser. withAllSessionsFiltered(filter, run); //注意这里调用了有filter功能的方法 } }
(5)WebSingleGamePushUtil 用于单发游戏
public class WebSingleGamePushUtil { public void push(final String customId,final String wId,final Webcast_game_push push){ Runnable run = new Runnable(){ private ScriptBuffer script = new ScriptBuffer(); public void run() { //设置要调用的 js及参数 script.appendCall( "show",JSONObject.fromObject(push).toString()); ScriptSession scriptSession =DWRScriptSessionListener.getScriptSession(customId+","+wId); if(null!=scriptSession){ scriptSession.addScript( script); } } }; //执行推送 Browser.withAllSessions(run); } }
(6)WebSinglePushUtil 用于单发通知
public class WebSinglePushUtil { public void push(final String customId,final String wId,final String content,final String command){ //过滤器 ScriptSessionFilter filter = new ScriptSessionFilter() { public boolean match(ScriptSession scriptSession) { String tagId=customId+","+wId; String tag = (String)scriptSession.getAttribute(tagId); if ( tag== null) { return false; } else { return tagId.equals(tag); } } }; Runnable run = new Runnable(){ private ScriptBuffer script = new ScriptBuffer(); public void run() { //设置要调用的 js及参数 script.appendCall( "show","{\"customId\":\""+customId+"\",\"wId\":\""+wId+"\",\"content\":\""+content+"\",\"command\":\""+command+"\"}"); //得到所有ScriptSession Collection<ScriptSession> sessions = Browser.getTargetSessions(); //遍历每一个ScriptSession for (ScriptSession scriptSession : sessions){ scriptSession.addScript( script); } } }; //执行推送 Browser. withAllSessionsFiltered(filter, run); //注意这里调用了有filter功能的方法 } }
4.在jsp页面引入相应的js
<script type="text/javascript" src="/worklite/dwr/engine.js"></script> <script type="text/javascript" src="/worklite/dwr/util.js"></script> <script type="text/javascript" src="/worklite/dwr/interface/DwrPush.js"></script> dwr.engine.setActiveReverseAjax(true); dwr.engine.setAsync(true); dwr.engine._errorHandler = function(message, ex) {dwr.engine._debug("Error: " + ex.name + ", " + ex.message, true);}; <body onload="dwr.engine.setActiveReverseAjax(true);dwr.engine.setNotifyServerOnPageUnload(true);onPageLoad();">
在页面上要先掉用下DwrPush.onPageLoad(),加入scriptSession
function onPageLoad(){ DwrPush.onPageLoad(wId); DwrPush.onPageLoad(""+customId+","+wId); }
然后在代码中调用相应的push方法即可完成推送。