Ajax的一个问题，求大神们回答！

Question

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

var xmlhttp;
function verify() {
var userName = document.getElementById("username").value;
if(window.XMLHttpRequest) {
xmlhttp = new XMLHttpRequest();
//针对某些特定版本的mozillar浏览器的BUG进行修复
if(xmlhttp.overrideMimeType) {
xmlhttp.overrideMimeType("text/xml");
}
} else if(window.ActiveXObject) {
var activeName = ["MSXML2.XMLHTTP","Micrisoft.XMLHTTP"];

    for(var i = 0; i < activeName.length; i++) {
        //尝试去创建对象，如果创建成功就终止循环
        //如果创建失败然后可以继续循环
        try {
            xmlhttp = new ActiveXObject(activeName[i]);
            break;
        } catch(e) {
    //      e.printStackTrace();
        }

    }
}
xmlhttp.onreadstatechange = callback;
xmlhttp.open("GET", "/AJaxTest/TelonVerify?username="+userName, true);
xmlhttp.send(null); 

}
function callback() {
//判断对象状态是否交互完成
alert("callback");
if(xmlhttp.readyState == 4) {
//判断http交互是否成功
if(xmlhttp.status == 200) {
//获取返回数据
var backText = xmlhttp.responseText;
var divNode = document.getElementById("backText");
divNode.innerHTML = backText;
}
}
}

public class TelonVerify extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setContentType("text/html;charset=utf-8");
PrintWriter out = resp.getWriter();
String userName = req.getParameter("username");
String name = new String(userName.getBytes("iso-8859-1"), "utf-8");

    if("123".equals(userName)) {
        out.println("用户名"+name+"已存在");
    } else {
        out.println("用户名"+name+"可以注册");
    }
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    this.doGet(req, resp);

}

}

Servlet能接受传过来的数据，但是不能out.println()写回到浏览器；
我调试了很久，还没有解决，求大神们回答

Answer 1

亲。你的代码。好多好乱啊。我有点看不懂了。平时写这个写得最多了。随便复制一个我的例子给你看看好了：
$("#firstKindId").change(function(){
var id=document.getElementById("firstKindId").value;
$("#secondKindId option:gt(0)").remove();
var id=$(this).val();
$.post('threeLevel.htm?time='+Math.random(),
{"id":id},
function(data){
var dataArray=eval(data);
for(var i=0;i $(""+dataArray[i].name+"").appendTo($("#secondKindId"));
}
});
});