DWR构建的简单聊天程序-供初学者学习
更新:HHH   时间:2023-1-7


DWR允许客户端脚本远程调用服务器端的类方法。使用它可以很容易的构建ajax程序。在此,简要说明一下如何通过DWR构建一个简单的一对一聊天程序。

1.首先配置web.xml


<!-- 配置spring -->
<context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/applicationContext*.xml</param-value>
</context-param>
<listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<!-- 配置DwrServlet -->
<display-name>DWR (Direct Web Remoting)</display-name>
<description>A Simple Demo DWR</description>
<servlet>
 <servlet-name>dwr-invoker</servlet-name>
 <servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
<init-param><!--开启debug为true后,可以通过访问ContextPath/dwr/index.html进行调试-->
      <param-name>debug</param-name>
      <param-value>true</param-value>
</init-param>
<init-param><!--该选项为true时,轮询和反向ajax会被启用-->
      <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>-1</param-value>
</init-param>                                                 
 <init-param><!--该参数为true时,允许远程服务器将javascript代码动态添加到客户端页面中-->
   <param-name>allowScriptTagRemoting</param-name>
   <param-value>true</param-value>
 </init-param>
 <load-on-startup>3</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>dwr-invoker</servlet-name>
    <url-pattern>/dwr/*</url-pattern>
</servlet-mapping>
  <!-- 监听scriptSession -->
  <servlet>
  <servlet-name>scriptSessionListener</servlet-name>
  <servlet-class>com.hb.util.InitScriptSessionListener</servlet-class>
  <load-on-startup>8</load-on-startup>
  </servlet>


2.配置dwr.xml

<create creator="spring" javascript="MessageService" scope="application">
      <param name="beanName" value="dwrMessageService"/>
 </create>
<convert converter="bean" match="com.entity.Message" />

dwr中create元素中creator属性为spring,表示,名为“dwrMessageService”的bean由spring进行管理,javascript属性值表示如何在客户端调用该bean,即通过该属性的值调用。dwr可以自动对javascript对象和java对象进行转化。convert元素的match属性即表示哪个java bean交由dwr进行互转。

3.spring配置文件如下

<bean id="dwrMessageService" class="com.dwr.MyMessageService" scope="prototype">
<property name="messageService">
 <ref bean="messageService"/>
</property>
</bean>

4.(1)com.dwr.MyMessageService类部分代码如下:


import com.util.initParam;
public boolean pushMessageToSomeOne(String userId,Message msg){
         /*将消息保存到数据库*/
           try {
               messageService.saveMessage(msg);
           } catch (Exception e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           }
//调用接收方客户端的showMessageFromOne(msg)函数,将msg消息传递给接收方
ScriptBuffer script = new ScriptBuffer();           script.appendScript("showMessageFromOne(").
appendData(msg).appendScript(");");
      ScriptSession s1= initParam.sc.get(userId); //获取接收方的ScriptSession
      s1.addScript(script);
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
           return true;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
       }

(2)com.util.initParam类

package com.util;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import org.directwebremoting.ScriptSession;
import com.dwr.ScriptSessionAndUser;
public class initParam {
 public static Map<String,ScriptSession> sc  =newHashMap<String,ScriptSession>();  // 保存用户id和该用户对应的ScriptSession
    public initParam(){}
}

(3)用来监听ScriptSession的Servlet:InitScriptSessionListener

package com.util;
import java.io.IOException;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpSession;
import org.directwebremoting.Container;
import org.directwebremoting.ScriptSession;
import org.directwebremoting.ServerContextFactory;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.event.ScriptSessionEvent;
import org.directwebremoting.event.ScriptSessionListener;
import org.directwebremoting.extend.ScriptSessionManager;
public class InitScriptSessionListener extends GenericServlet {
   /* 监控ScriptSessionListener状态*/
 public void init()
    {
 Container container = ServerContextFactory.get().getContainer();
 ScriptSessionManager manager =container.getBean(ScriptSessionManager.class);
ScriptSessionListener listener = new AddScriptSessionListener();
        manager.addScriptSessionListener(listener);
    }
    @Override
    public void service(ServletRequest arg0, ServletResponse arg1)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        init();
                                                                                                                                                                                                                                                                                                                                                                                                                         
    }
                                                                                                                                                                                                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                                                                                                                                                     
}

(4)AddScriptSessionListener类


package com.util;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import javax.servlet.http.HttpSession;
import org.directwebremoting.ScriptSession;
import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.event.ScriptSessionEvent;
import org.directwebremoting.event.ScriptSessionListener;
public class AddScriptSessionListener implements ScriptSessionListener{
    public void sessionCreated(ScriptSessionEvent se) {
 /*客户端刷新页面后,将用户的session信息和ScriptSession重新绑定*/       
WebContext ct = WebContextFactory.get();
HttpSession session =ct.getHttpServletRequest().getSession();
initParam.sc.put(session.getAttribute("UsersId").toString(),
se.getSession());
                                                                                                                                                                                                                                                                                                                                                                                                 
    public void sessionDestroyed(ScriptSessionEvent se) {
        System.out.println(se.getSession()+"销毁");
    }
                                                                                                                                                                                                                                                                                                                                                                                             
}

5.客户端代码


<script type="text/javascript" src="<%=basePath%>dwr/engine.js"</script>
<script type="text/javascript" src="<%=basePath%>dwr/interface/MessageService.js"></script>
<script type="text/javascript">
   dwr.engine.setActiveReverseAjax(true);   //启用dwr反向ajax
   dwr.engine.setNotifyServerOnPageUnload(true);//刷新页面后销毁当前scriptsession
   dwr.engine.setErrorHandler(function()
           {
       //alert("错误");
           }); //自定义错误处理方式
  function sendMessageTo(userId)
  {
 var content=document.getElementById("content").innerHTML;
 document.getElementById("content").innerHTML="";
document.getElementById("message").innerHTML=getId("message").innerHTML+"<li><span>${session.username}"+content+"</span></li>";
var msg={};
msg.getId=userId;
msg.content=content;
msg.sendId=${session.userId};//将发送的信息显示到信息框
MessageService.pushMessageToSomeOne(userId,msg,function(data){});
//通过MessageService对象调用远程MyMessageService类的 public boolean pushMessageToSomeOne(String userId,Message msg)方法,最后一个参数为回调函数
  }
 function showMessageFromOne(msg)
  { var htmls="<li><span>"+msg.sendId+"+msg.content+"</span></li>";       document.getElementById("message").innerHTML=document.getElementById("message").innerHTML+htmls+"<br />";
          }
    }
<script type="text/javascript" src="<%=basePath%>dwr/engine.js"</script>
<script type="text/javascript" src="<%=basePath%>dwr/interface/MessageService.js"></script>
<script type="text/javascript">
   dwr.engine.setActiveReverseAjax(true);   //启用dwr反向ajax
   dwr.engine.setNotifyServerOnPageUnload(true);//刷新页面后销毁当前scriptsession
   dwr.engine.setErrorHandler(function()
           {
       //alert("错误");
           }); //自定义错误处理方式
  function sendMessageTo(userId)
  {
 var content=document.getElementById("content").innerHTML;
 document.getElementById("content").innerHTML="";
document.getElementById("message").innerHTML=getId("message").innerHTML+"<li><span>${session.username}"+content+"</span></li>";
var msg={};
msg.getId=userId;
msg.content=content;
msg.sendId=${session.userId};//将发送的信息显示到信息框
MessageService.pushMessageToSomeOne(userId,msg,function(data){});
//通过MessageService对象调用远程MyMessageService类的 public boolean pushMessageToSomeOne(String userId,Message msg)方法,最后一个参数为回调函数
  }
}
<div id="container">
<div id="message"></div>
<div id="content"></div>
<input type="button" data-role="button"  onclick="sendMessageTo(${getUsers.id})">发送</a>
</div>


6.现在解释一下ScriptSession.我们知道,一般的Session会在用户初次访问时创建,然后在用户的整个访问过程中一直存在,直到用户在一定时间内未进行任何访问后销毁。 而DWR中的ScriptSession则是用户每次刷新或重新请求一个dwr控制的页面时,重新创建。因此,在本例中我们创建了ScriptSession的监听器,每当重新创建新的ScriptSession时,将当前用户的session与新的ScriptSession重新绑定,以便可以确切的将消息发送给目标用户,而不是调用一个已经不存在的ScriptSession。 通过在页面加载后调用dwr.engine.setNotifyServerOnPageUnload(true);可以使DWR在创建一个新的ScriptSession后自动销毁之前的ScriptSession。

7.本例是本人在测试的项目当中挖取的一部分主要内容,可能不够全面,也存在一些问题。望大家批评指正。谢谢。

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