dwr实现消息精准推送
关于dwr具体概念本文不做赘述，只谈实现。在参考了好几篇网上的博文后，把dwr整合到我的项目里面了，跑起来也没有问题。java推送有许多实现方式，诸如comet4j，websocket等等，还有一些收费的比如goeasy等，有兴趣朋友可以看看，废话不多说开始实现。
一：项目的应用场景
在项目里面有一个审批流程，上级领导把一个线索分配给下级实现，中途还可以变更下级，这样一来就会出现原来的下级正在对线索进行操作，而该线索已经不属于他，这时候我们需要一个消息实时推送给原来的下级，告诉他线索不属于你你甭干了，乖乖去玩吧！
二：实现
1：maven项目引入jar包，非maven项目去dwr官网下载
<dependency> <groupId>org.directwebremoting</groupId> <artifactId>dwr</artifactId> <version>3.0.2-RELEASE</version> </dependency>
2：在web.xml配置
<!-- dwr的配置 -->
<servlet>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
<init-param>
<param-name>debug</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>activeReverseAjaxEnabled</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>pollAndCometEnabled</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>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dwr-invoker</servlet-name>
<url-pattern>/dwr/*</url-pattern>
</servlet-mapping>
3：编写一个java类，用于要通知的页面把用户id传入保存session，这样服务端才能知道给谁发
public class MessagePush {
public void onPageLoad(String userId) {
ScriptSession scriptSession = WebContextFactory.get().getScriptSession();
scriptSession.setAttribute("userId", userId); //把前台传入的id保存
DwrScriptSessionManagerUtil dwrScriptSessionManagerUtil = new DwrScriptSessionManagerUtil();
try {
dwrScriptSessionManagerUtil.init();
} catch (ServletException e) {
e.printStackTrace();
}
}
}
还需要一个DwrScriptSessionManagerUtil工具类
import javax.servlet.ServletException;
import javax.servlet.http.HttpSession;
import org.directwebremoting.Container;
import org.directwebremoting.ServerContextFactory;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.event.ScriptSessionEvent;
import org.directwebremoting.event.ScriptSessionListener;
import org.directwebremoting.extend.ScriptSessionManager;
import org.directwebremoting.servlet.DwrServlet;
/**
* @author Administrator
*
*/
public class DwrScriptSessionManagerUtil extends DwrServlet{
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) {
HttpSession session = WebContextFactory.get().getSession();
String userId = (String) session.getAttribute("userId");
System.out.println(">>>>>>>>>a ScriptSession is created!");
ev.getSession().setAttribute("userId", userId);
}
public void sessionDestroyed(ScriptSessionEvent ev) {
System.out.println(">>>>>>>>a ScriptSession is distroyed");
}
};
manager.addScriptSessionListener(listener);
}
}
4:在与web.xml同级的目录下新建一个dwr.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC
"-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN"
"http://directwebremoting.org/schema/dwr30.dtd">
<dwr>
<allow>
<create javascript="MessagePush" creator="new">
<param name="class" value="com.gtcity.web.util.MessagePush"></param>
</create>
</allow>
</dwr>
value="com.gtcity.web.util.MessagePush"代表对应的java类，javascript="MessagePush"代表页面引用的js名称，dwr目的就是要让js调用java方法
5：需要通知的页面
<script type="text/javascript" src="${pageContext.request.contextPath }/dwr/engine.js"></script>
<script type="text/javascript" src="${pageContext.request.contextPath }/dwr/util.js"></script>
<script type="text/javascript" src="${pageContext.request.contextPath }/dwr/interface/MessagePush.js"></script>这几个写法就是写死的，就是第三个*.js需要对应你在第4步上javascript="MessagePush"里面定义的名字
<body style="overflow-x:hidden;" onload="dwr.engine.setActiveReverseAjax(true);dwr.engine.setNotifyServerOnPageUnload(true);onPageLoad();">
这几个也是必须的
function onPageLoad(){
var userId = '${user.userId}';
MessagePush.onPageLoad(userId);
}
//推送信息
function showMessage(autoMessage){
alert(autoMessage);
}
6：具体写消息推送的类，结合自身项目情景，我这里是在上级更改了下级后写的
A：给一个人发
//修改成功给张三发消息
final String userId = "2"; //这个我写死张三userId=2
final String autoMessage = "上级已经更改了这条线索的归属人了！";
Browser.withAllSessionsFiltered(new ScriptSessionFilter() {
public boolean match(ScriptSession session){ //验证符合条件的发送人
if (session.getAttribute("userId") == null){
return false;
}else {
return (session.getAttribute("userId")).equals(userId);
}
}
}, new Runnable(){
private ScriptBuffer script = new ScriptBuffer();
public void run(){
script.appendCall("showMessage", autoMessage);
Collection<ScriptSession> sessions = Browser
.getTargetSessions();
for (ScriptSession scriptSession : sessions){
scriptSession.addScript(script);
}
}
});
B：给多个人
//修改成功给张三，李四发消息
final String userId = "2,3,***";
final String autoMessage = "上级已经更改了这条线索的归属人了！";
Browser.withAllSessionsFiltered(new ScriptSessionFilter() {
public boolean match(ScriptSession session){
if (session.getAttribute("userId") == null){
return false;
}else {
String attribute = (String) session.getAttribute("userId");
return (userId.contains(attribute));
}
}
}, new Runnable(){
private ScriptBuffer script = new ScriptBuffer();
public void run(){
script.appendCall("showMessage", autoMessage);
Collection<ScriptSession> sessions = Browser
.getTargetSessions();
for (ScriptSession scriptSession : sessions){
scriptSession.addScript(script);
}
}
});
至此，dwr精准推送完毕。如果还想进一步结合spring有兴趣可以看看这篇文章 springMVC+dwr3 实现精确推送信息（2种方法）