小玩dwr实现服务器推送

最近项目有需要用到‘推’，就是服务器端自动把消息推给客户端，就做了个不像样的dwr实现的服务器推送demo，玩玩...

首先少不了dwr的jar包。
然后是在项目中建个dwr.xml的配置文件，当然，同时需要在web.xml中配置。

贴上代码：
web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
	http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
	<servlet>
		<servlet-name>DwrServlet</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>pollAndCometEnabled</param-name>
			<param-value>true</param-value>
		</init-param>
		<load-on-startup>12</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>DwrServlet</servlet-name>
		<url-pattern>/dwr/*</url-pattern>
	</servlet-mapping>


	<welcome-file-list>
		<welcome-file>index.jsp</welcome-file>
	</welcome-file-list>

</web-app>

配置也没什么好解释的，
然后在工程中创建了两个类：

package dwr.reverseAjax;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import javax.servlet.http.HttpSession;

import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.proxy.dwr.Util;
import org.directwebremoting.util.Logger;

import dwr.reverse.StocksPusher;

public class DWRAjaxReverse implements Runnable {
	public static List<DWRAjaxReverse> store = new ArrayList<DWRAjaxReverse>();
	WebContext wctx = null;
	public String currentPage = "";
	private static final Logger log = Logger.getLogger(DWRAjaxReverse .class);

	@SuppressWarnings("unchecked")
	public DWRAjaxReverse() {
		ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(
				1);
		executor.scheduleAtFixedRate(this, 1, 7000, TimeUnit.MILLISECONDS);

		wctx = WebContextFactory.get();
		HttpSession session = wctx.getSession();
		List<DWRAjaxReverse> list = (List<DWRAjaxReverse>) session
				.getAttribute("DWRHelper");
		if (list == null)
			list = new ArrayList<DWRAjaxReverse>();
		list.add(this);
		store.add(this);
	}

	@SuppressWarnings("unchecked")
	public void addMessage(String text) {
		LinkedList messages = new LinkedList();
		if (text != null && text.trim().length() > 0) {
			messages.addFirst(new Message(text));
			while (messages.size() > 10) {
				messages.removeLast();
			}
		}
		wctx = WebContextFactory.get();
		currentPage = wctx.getCurrentPage();

		Util utilThis = new Util(wctx.getScriptSession());
		utilThis.setValue("text", "");

		Collection sessions = wctx.getScriptSessionsByPage(currentPage);
		Util utilAll = new Util(sessions);

		utilAll.removeAllOptions("chatlog");
		// utilAll.addOptions("chatlog", messages, "text");
		utilAll.addFunctionCall("reverseAjax", text);
	}

	@SuppressWarnings("unchecked")
	@Override
	public void run() {
		if (true) {
			log.info("run...");
			Collection sessions = wctx.getScriptSessionsByPage(currentPage);
			Util utilAll = new Util(sessions);
			Date date = new Date();
			LinkedList lst = new LinkedList();
			lst.add(new Message(date.toString()));
			// utilAll.setValue("text", date.toString());
			//utilAll.removeAllOptions("chatlog");
			//utilAll.addOptions("chatlog", lst, "text");
			utilAll.addFunctionCall("reverseAjax", date.toString());
			log.info("current time is : "+date.toString());
		}
	}

}

package dwr.reverseAjax;

import org.directwebremoting.Security;

public class Message {
	private String text;
	private long id = System.currentTimeMillis();
	
	public Message(String newText){
		text = newText;
		if(text.length()>256){
			text = text.substring(0,256);
		}
		text = Security.replaceXmlCharacters(text);
	}

	public String getText() {
		return text;
	}

	public void setText(String text) {
		this.text = text;
	}

	public void setId(long id) {
		this.id = id;
	}

	public long getId() {
		return id;
	}
}

主要操作都在DWRAjaxReverse类中。

然后就是在dwr.xml中配置了，

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://getahead.org/dwr/dwr20.dtd">
<dwr>
	<allow>
	
		<create creator="new" javascript="DWRAjaxReverse">
			<param name="class" value="dwr.reverseAjax.DWRAjaxReverse" />
			<include method="addMessage" />
		</create>
		<convert converter="bean" match="dwr.reverseAjax.Message">
			<param name="include" value="id,text" />
		</convert>


	</allow>
</dwr>

用过dwr的人这个配置你懂的！


现在写个简单的jsp，

<h1>
	DWR AjaxReverse
</h1>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
	<script type='text/javascript' src='/stock/dwr/engine.js'></script>
	<script type='text/javascript' src='/stock/dwr/util.js'></script>
	<script type='text/javascript' src='/stock/dwr/interface/DWRAjaxReverse.js'></script>
	
	<body onload="dwr.engine.setActiveReverseAjax(true);init()">
	
	<script type="text/javascript">
	
	function reverseAjax(messages){
		document.getElementById('time_text').innerHTML= messages;
	}

	function init() {
		DWRAjaxReverse.addMessage("you are welcome!");
	}
</script>
	<hr />
	<ul id="chatlog" style="list-style-type: none;" >
	</ul>
	<span id='time_text' ></span>
	
</body>

不要问我/stock/dwr/engine.js 这样在工程中看不到的js在哪，玩dwr这个是要懂的(其实我也不懂，只知道dwr会自己虚拟的创建)

dwr.engine.setActiveReverseAjax(true) 这句在你的前台页面是不能少的

其中，reverseAjax这个function就是给后台调用的，后台调用前台
到此，这么个demo也算像个样子了