Ajax 返回值 中文乱码 解决

/**
* 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>");
});
}
});