急啊！为什麽功能实现不了？！

附上我的代码，我要实现的功能是，一个列表，当鼠标放到列表某一行，会自动弹出一个提示框，给出相关信息。client side是javascript,server side是java 服务器是apache.哪里出错了？那位大侠给指点一下！急啊！！！client side:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>
  <head>
    <title>Ajax Tooltip</title>
    <script type="text/javascript">        
        var xmlHttp;
        var dataDiv;
        var dataTable;
        var dataTableBody;
        var offsetEl;        function createXMLHttpRequest() {
            if (window.ActiveXObject) {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            else if (window.XMLHttpRequest) {
                xmlHttp = new XMLHttpRequest();                
            }
        }        function initVars() {
            dataTableBody = document.getElementById("courseDataBody");            
            dataTable = document.getElementById("courseData");
            dataDiv = document.getElementById("popup");
        }        function getCourseData(element) {
            initVars();            
            createXMLHttpRequest();
            offsetEl = element;
            var url = "ToolTipServlet?key=" + escape(element.id);
            
            xmlHttp.open("GET", url, true);
            xmlHttp.onreadystatechange = callback;
            xmlHttp.send(null);
        }        function callback() {
            if (xmlHttp.readyState == 4) {
                if (xmlHttp.status == 200) {
                    setData(xmlHttp.responseXML);
                }
            }
        }
        
        function setData(courseData) {            
            clearData();
            setOffsets();
            var length = courseData.getElementsByTagName("length")[0].firstChild.data;
            var par = courseData.getElementsByTagName("par")[0].firstChild.data;
            
            var row, row2;
            var parData = "Par: " + par
            var lengthData = "Length: " + length;
            
            row = createRow(parData);            
            row2 = createRow(lengthData);
            
            dataTableBody.appendChild(row);
            dataTableBody.appendChild(row2);
        }        function createRow(data) {            
            var row, cell, txtNode;
            row = document.createElement("tr");
            cell = document.createElement("td");            cell.setAttribute("bgcolor", "#FFFAFA");
            cell.setAttribute("border", "0");                                       txtNode = document.createTextNode(data);
            cell.appendChild(txtNode);
            row.appendChild(cell);
           
            return row;  
        }
        
        function setOffsets() {
            var end = offsetEl.offsetWidth;
            var top = calculateOffsetTop(offsetEl);
            dataDiv.style.border = "black 1px solid";
            dataDiv.style.left = end + 15 + "px";
            dataDiv.style.top = top + "px";
        }
        
        function calculateOffsetTop(field) {
          return calculateOffset(field, "offsetTop");
        }        function calculateOffset(field, attr) {
          var offset = 0;
          while(field) {
            offset += field[attr]; 
            field = field.offsetParent;
          }
          return offset;
        }        function clearData() {            
            var ind = dataTableBody.childNodes.length;            
            for (var i = ind - 1; i >= 0 ; i--) {
                dataTableBody.removeChild(dataTableBody.childNodes[i]);       
            }
            dataDiv.style.border = "none";
        }        
    </script>
  </head>
  <body>
    <h1>Ajax Tooltip Example</h1>
    <h3>Golf Courses</h3>
    <table id="courses" bgcolor="#FFFAFA" border="1" cellspacing="0" cellpadding="2"/>
        <tbody>
            <tr><td id="1" onmouseover="getCourseData(this);" onmouseout="clearData();">Augusta National</td></tr>
            <tr><td id="2" onmouseover="getCourseData(this);" onmouseout="clearData();">Pinehurst No. 2</td></tr>
            <tr><td id="3" onmouseover="getCourseData(this);" onmouseout="clearData();">St. Andrews Links</td></tr>
            <tr><td id="4" onmouseover="getCourseData(this);" onmouseout="clearData();">Baltusrol Golf Club</td></tr>
        </tbody>        
    </table>
    <div style="position:absolute;" id="popup">
        <table id="courseData" bgcolor="#FFFAFA" border="0" cellspacing="2" cellpadding="2"/>
            <tbody id="courseDataBody"></tbody>
        </table>
    </div>  </body>
</html>server side:ToolTipServlet.javaimport java.io.*;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.*;
import javax.servlet.http.*;
public class ToolTipServlet extends HttpServlet {
    
    private Map courses = new HashMap();
    public void init(ServletConfig config) throws ServletException {
        CourseData augusta = new CourseData(72, 7290);
        CourseData pinehurst = new CourseData(70, 7214);
        CourseData standrews = new CourseData(72, 6566);
        CourseData baltusrol = new CourseData(70, 7392);
        courses.put(new Integer(1), augusta);
        courses.put(new Integer(2), pinehurst);        
        courses.put(new Integer(3), standrews);        
        courses.put(new Integer(4), baltusrol);
    }
   
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {        
Integer key = Integer.valueOf(request.getParameter("key"));       
CourseData data = (CourseData) courses.get(key);                
PrintWriter out = response.getWriter();       
response.setContentType("text/xml");       
response.setHeader("Cache-Control", "no-cache");        
out.println("<response>");        
out.println("<par>" + data.getPar() + "</par>");        
out.println("<length>" + data.getLength() + "</length>");        
out.println("</response>");        
out.close();    
}           
private class CourseData {       
private int par;       
private int length;                
public CourseData(int par, int length) {            
this.par = par;            
this.length = length;        
}                
public int getPar() {            
return this.par;        
}               
public int getLength() {            
return this.length;       
}    
}
}