怎么样在JSP中结合js实现img中src更新请求？

<script type="text/javascript"> 
function changeImage(){ 
 var img = document.getElementById("imgVcode");
 if(img.name == 1){ 
  img.name = 2; 
  img.src = "shop.do?method=registerImage2";
 }else if(img.name == 2){ 
  img.name = 1; 
  img.src = "shop.do?method=registerImage";
 } 
} 
</script>

<td> 
 <img class="yzm_img" id='imgVcode' name="1" src="shop.do?method=registerImage" />
 <input name="code" type="text" id="txtVerifyCode" 
  class="yzm_input" onblur="testCode(this)"/>
 <div class="text_left t1">
  <p class="t1">
   <span id="vcodeValidMsg">请输入图片中的四个字母。</span> 
   <span id="codeInfo" style="color:red"></span> 
   <a href="#" id="imgchange" onclick="changeImage()">看不清楚？换个图片</a>
  </p> 
 </div> 
</td>

public ActionForward registerImage(ActionMapping mapping, ActionForm form, 
  HttpServletRequest request, HttpServletResponse response)
  throws Exception { 
  //将image创建,返回认证码 
  response.setContentType("image/jpeg"); 
  OutputStream out = response.getOutputStream(); 
  String strEnsure = shopManager.createImageInfo(50,20,out);
  //设置到session中 
  request.getSession().setAttribute("strEnsure", strEnsure);
  return null; 
 } 
 public ActionForward registerImage2(ActionMapping mapping, ActionForm form, 
   HttpServletRequest request, HttpServletResponse response)
   throws Exception { 
  //将image创建,返回认证码 
  response.setContentType("image/jpeg"); 
  OutputStream out = response.getOutputStream(); 
  String strEnsure = shopManager.createImageInfo(50,20,out);
  //设置到session中 
  request.getSession().setAttribute("strEnsure", strEnsure);
  return null; 
}