dwr初学者问题

我在eclipse环境下发布了个很简单的DWR项目，jdk1.6,tomcat6.0 ,dwr3.0 
以下是具体代码：
web-xml :
 <servlet>
    <servlet-name>dwr-invoker</servlet-name>
    <servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
  </servlet> 
  <servlet-mapping>
    <servlet-name>dwr-invoker</servlet-name>
    <url-pattern>/dwr/*</url-pattern>
   </servlet-mapping>
</web-app>
dwr.xml:
<dwr>
 <allow> 
    <create creator="new" javascript="Hello" scope='application'> 
      <param name="class" value="com.newer.caterpiller.Hello"/> 
    </create> 
  </allow> 
</dwr>
src中:
package com.newer.caterpiller;public class Hello {
public String sayHello(String name) {
return "你好：" + name;
}
}
页面:
<head>
  <script type='text/javascript' src='dwr/interface/Hello.js'></script> 
  <script type='text/javascript' src='dwr/engine.js'></script> 
  <script type='text/javascript' src='dwr/util.js'></script> 
  <script type="text/javascript" >
    function send()
    {
     var user = dwr.util.getValue('name');
     Hello.sayHello(user,show);
    }
    function show(msg)
    {
     alert(msg);
    }
  </script>
  </head>
  <body>
    <input type='text'  id='name'/> <input type='button' value='说' onclick = 'send();'/>
    <div id='statement' ></div> 
  </body>
为什么我运行总是提示：
'dwr'  is undifined.
麻烦各位前辈帮下我！在下实在穷困，分少见谅!