/**
* 使用ajax检查用户是否存在
*/
public void checkUser(){

try{
System.out.println("userName="+user.getUserName());
HttpServletResponse response=ServletActionContext.getResponse();
response.setContentType("text/xml;charset=utf-8");
response.setHeader("Cache-Control","no-cache");

PrintWriter pw=response.getWriter(); //输出中文，这一句一定要放到response.setContentType("text/xml;charset=utf-8"),response.setHeader("Cache-Control","no-cache")后面，否则中文返回到页面是乱码 if(existUser.contains(user.getUserName())) { pw.print("存在"); }else{ pw.print("不存在"); } pw.close(); }catch(IOException e){ e.printStackTrace(); } } 前台： $.ajax({ type: "POST",url : "${contextPath?if_exists}/resource/cascade.action",data: {firstType:filrstTypevl},contentType:"application/x-www-form-urlencoded;charset=utf-8",dataType: "json",success: function(resp) { $("#secondType option").remove(); $("#secondType").append("<option value=''>－－请选择二级分类－－</option>"); alert(resp); $.each(resp,function(i){ $("#secondType").append("<option value="+resp[i].kdDetail+">"+resp[i].kdDesc+"</option>"); }); } });