<script type="text/javascript">   
        /*
            注册dojo事件用来显示验证码
        */              
        dojo.addOnLoad(function() {
          dojo.event.topic.subscribe('/retrieveUser', this, function(data, type, e){
          if(type == 'load') {
                    showUser(data);
                } else if(type == 'error') {
                    alert('Can not retrieve the Vocde');
                }
            });
        });
        function showUser(strUser) {      
            var UserHolder = document.getElementById('im');
            UserHolder.src ='getVocde.action';
            
        }
        </script>

<s:url id="userUrl" value="getVocde.action" />
<td colspan="2">
                                    验证码
                                    <input maxlength="4" size="2" name="logon.vcode">
                                    <img border="0" src="getVocde.action" width="57" height="22" id="im" 
                                        align="middle">
                                    <a target="main" href="MyCountManager/BSP_User_getpass.jsp">&nbsp;找回密码</a>&nbsp;&nbsp;
                                    <sx:a  href="%{userUrl}"  notifyTopics="/retrieveUser">看不清,换一张</sx:a>

@Action(value ="getVocde", results = {@Result(name = "input",  type = "stream",params={"contentType", "image/jpeg", "contentDisposition", "filename=document.jpeg","bufferSize", "1024"})})
    public String execute()throws IOException {
        VImage v=new VImage();          //这是生成验证码的servlet
        try {
            v.doGet(ServletActionContext.getRequest(), ServletActionContext.getResponse());
        } catch (ServletException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return "input";
    }