DWR2中調用Servlet相關類（簡單例子）

DWR2一大特性就是在DWR中可以通路WEB上下文的SERVLET，REQUEST等，主要用到的類是WebContext,WebContextFactory，使用WebContextFacotry.get()方法得到目前的WebContext，原理是将WebContext與目前thread綁定，内部使用ThreadLocal來維護。

use case：

在IE中使用JAVASCRIPT來判斷制定使用者名經是否已經登陸。

client(index.jsp)

<% @ page language = " java "   import = " java.util.* "  pageEncoding = " gb2312 " %>

<%

String path  =  request.getContextPath();

String basePath  =  request.getScheme() + " :// " + request.getServerName() + " : " + request.getServerPort() + path + " / " ;

// 為示範:假設已經登入成功

request.getSession( true ).setAttribute( " cur_user " , " jack " );

%>

<! DOCTYPE HTML PUBLIC  " -//W3C//DTD HTML 4.01 Transitional//EN " >

< html >

   < head >

     < base href = " <%=basePath%> " >

     < script type = ' text/javascript '  src = ' dwr/engine.js ' >   </ script >

     < script type = ' text/javascript '  src = ' dwr/util.js ' >   </ script >

     < script type = ' text/javascript '  src = ' dwr/interface/UserCheck.js ' >   </ script >

     < script language = " javascript " >

        function checkUserIsLogin(name)  ... {

            UserCheck.checkUserIsLogin(name,function(res) ...{

                    var retMsg = ( true == res ) ? "已經登入" : "未登入";

                    DWRUtil.setValue("msg",retMsg);

                }

            );

        }

     </ script >

   </ head >

   < body >

    < input type = " text "  name = " username "   />< input type = " button "  value = " check "  onclick = " checkUserIsLogin(document.all.username.value) "   /> 目前session中儲存為jack

    < br />

    < div id = " msg " ></ div >

   </ body >

</ html >

服務端：UserCheckUtil.java

package  com.dwr;

import  javax.servlet.http.HttpSession;

import  org.directwebremoting.WebContext;

import  org.directwebremoting.WebContextFactory;

public   class  UserCheckUtil  ... {

    public boolean checkUserIsLogin(String username) ...{

        WebContext ctx = WebContextFactory.get();

        HttpSession session = ctx.getSession(false);

        if (null != session && username.equals(String.valueOf(session.getAttribute("cur_user"))))

            return true;

        else

            return false;

    }

}

配置檔案：dwr.xml

<? 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 ="UserCheck" >

       < param  name ="class"  value ="com.dwr.UserCheckUtil" />

     </ create >

   </ allow >

</ dwr >