dwr消息推送

闲来无事，把自己关于对dwr消息推送的实现过程描述一番。

首先第一步，当然在工程中是加入dwr.jar了，接着在web.xml中配置以下代码

<servlet>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
<init-param>
<param-name>config</param-name>
<param-value>/WEB-INF/config/dwr.xml</param-value>
</init-param>
<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>classes</param-name>
<param-value>java.lang.Object</param-value>
</init-param>
<init-param>
<param-name>activeReverseAjaxEnabled</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>initApplicationScopeCreatorsAtStartup</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>maxWaitAfterWrite</param-name>
<param-value>3000</param-value>
</init-param>
<init-param>
<param-name>logLevel</param-name>
<param-value>WARN</param-value>
</init-param>
<load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dwr-invoker</servlet-name>
<url-pattern>/dwr/*</url-pattern>
</servlet-mapping>

从配置中可以看出需要新建一个dwr配置文件，如下

<?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 javascript="udao" creator="spring"> <param name="beanName"
value="udao" /> <include method="getUserPage"/> </create> <convert converter="bean"
match="com.cpsoft.app.web.domain.PageModel" /> -->

<create javascript="MessagePush" creator="spring">
<param name="beanName" value="messagePush" />
</create>
<convert converter="bean" match="java.lang.StackTraceElement" />
<convert converter="exception" match="java.lang.Exception" />
</allow>
</dwr>

那么大家可以看到，我配置了一个messagePush这个对象，那么我就来说说这个对象吧

@Component
public class MessagePush {

final public static String SCRIPT_SESSION_USERID = "SCRIPT_SESSION_USERID";
final public static String SCRIPT_SESSION_MSG = "showMessage"; //这是页面上当后台消息推送时，自动触发的js方法名称

private Logger log = Logger.getLogger(this.getClass());
private ScriptSessionListener listener;
private boolean isInit = false;

public boolean isInit(){
return isInit;
}
/**
* 获取scriptSession的监听对象，只需要实例化一次
* @return
*/
public ScriptSessionListener getListener() {
if(listener == null){
listener = new ScriptSessionListener() {
public void sessionCreated(ScriptSessionEvent ev) {
HttpSession session = WebContextFactory.get().getSession();
Staff staff = SessionUtil.getStaff(session);
if(staff!=null){
ev.getSession().setAttribute(SCRIPT_SESSION_USERID, staff.getId()); //与当前登录用户相关联
log.info("a ScriptSession["+staff.getId()+"] is created!");
Map<String, Staff> onlineStaffMap = CacheUtil.getOnlineStaffMap(); //获取当前的在线用户
if(!onlineStaffMap.containsKey(staff.getId())) onlineStaffMap.put(staff.getId(), staff); //如果不存在，则将当前用户加入到缓存中
}
if(!isInit) isInit = true;
}

public void sessionDestroyed(ScriptSessionEvent ev) {
String userId = (String) ev.getSession().getAttribute(SCRIPT_SESSION_USERID);
log.info("a ScriptSession["+userId+"] is distroyed!");
}
};
}
return listener;
}

/**
* 初始化dwr监听，只在程序中调用一次即可
*/
public void init(){
if(listener == null){
Container container = ServerContextFactory.get().getContainer();
ScriptSessionManager manager = container
.getBean(ScriptSessionManager.class);
manager.addScriptSessionListener(getListener());
log.info("the dwr client is inited!");
}
}

}

这个类的主要作用是初始化监听，接着如果有了监听，那现在就可以推送消息了，请看代码

/**
* 采用dwr的方式向前台推送消息
* @param userId 用户Id
* @param autoMessage 消息内容
*/
private static void sendMessageAuto(final String userId, final String autoMessage) {
Browser.withAllSessionsFiltered(new ScriptSessionFilter() {
public boolean match(ScriptSession session) {
String id = (String) session.getAttribute(MessagePush.SCRIPT_SESSION_USERID);
if (id == null || !userId.equals(id)) { //匹配接收人的Id
return false;
}
return true;
}
}, new Runnable() {
private ScriptBuffer script = new ScriptBuffer();
public void run() {
script.appendCall(MessagePush.SCRIPT_SESSION_MSG, autoMessage); //推送消息(我在这里用的是json字符串)
Collection<ScriptSession> sessions = Browser.getTargetSessions(); //获取当前的目标客户端对象
for (ScriptSession scriptSession : sessions) {
scriptSession.addScript(script);
}
}
});
}

说到这里，后台工作就告一段落了，接着来说说前台，首先引入js吧

<!-- 消息推送 -->
<script type='text/javascript' src='${ctx}/dwr/engine.js'></script>
<script type='text/javascript' src='${ctx}/dwr/util.js'></script>
<script type="text/javascript" src="${ctx}/dwr/interface/MessagePush.js"></script>

在onload 加入

<body onload="dwr.engine.setActiveReverseAjax(true);dwr.engine.setNotifyServerOnPageUnload(true);">

那么现在大工告成了，只要后台调用上面的推送方法，前台就好自动触发

function showMessage(autoMessage){
//alert(autoMessage);
if(!callCometShowMsg){
eval("var json="+ autoMessage);
g_showTip("消息类型:"+json.MESSAGE_TYPE+"<br />消息内容:"+json.MESSAGE_DATA);
}else{
callCometShowMsg(autoMessage);
}
}

最后说说总结一下把，实测了一下，发现Ie8下反应慢一点，对于chrome，我用的这个版本会有问题， 火狐表现良好

有什么问题可以留言，看到第一时间回复