Ajax校验是否重复的实现代码有哪些？

@ResponseBody 
@RequestMapping("entityFindByCode") 
public String entityFindByCode(Entity bean, HttpSession httpSession, Model m,HttpServletResponse res) throws IOException{ 
 res.setContentType("text/plain; charset=UTF-8"); 
 //res.reset(); 
 //PrintWriter out = res.getWriter(); 
 String data=null; 
 @SuppressWarnings("unchecked") 
 List<Entity> list = (List<Entity>) this.service.find("beanByCode", "Entity", new Object[]{bean.getCode()}); 
 if(list.size()==0){ 
  data="YES"; 
 }else{ 
  data="NO"; 
 } 
 res.getOutputStream().write(data.getBytes()); 
 //out.print(data); 
 //out.flush(); 
 //out.close(); 
 return data; 
}

$.ajax({ 
   url  :'entityFindByCode', 
   type  :'post', 
   dataType :'text', 
   data  :{code:$("#code").val()},//{key,value} 
   success :function(data) { 
    if (data == "YES"){ 
     document.getElementById("msg-code").innerHTML = "(<fmt:message key='warn.field.required.unique' bundle='${bundle }' />)"; 
     return true; 
    } 
    else { 
     $("#div-code").addClass("has-error"); 
     document.getElementsByName("code")[0].value = ""; 
     //document.getElementsByName("code")[0].setAttribute("placeholder", "<fmt:message key='warn.duplicate' bundle='${bundle }' />"); 
     document.getElementById("msg-code").innerHTML = "(<fmt:message key='warn.duplicate' bundle='${bundle }' /> !!!)"; 
     return false; 
    } 
   } 
  });