@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; 
        } 
      } 
    });