<script language="javascript">
        var xmlHttpRes;  
          
        function createXMLHttpRequest() {
            if(window.XMLHttpRequest) {  
                xmlHttpRes = new XMLHttpRequest();  
            } else if(window.ActiveXObject) {  
                xmlHttpRes = new ActiveXobject("Microsoft.XMLHTTP");  
            }
        }  
          
        function selectchange() {
            createXMLHttpRequest();  
            var department = document.getElementById("department").value;
            var url = "selectChangeServlet?department=" + department;
            xmlHttpRes.open("post", url, true);  
            xmlHttpRes.onreadystatechange = callback;  
            xmlHttpRes.send(null);  
        }  
          
        function callback() { 
            if(xmlHttpRes.readyState == 4) {  
                if(xmlHttpRes.status == 200) {
                    eval(xmlHttpRes.responseText);  
                }  
            }  
        }
        function show(){
            var department = document.getElementById("department").value;
            var classInfo = document.getElementById("classInfo").value;
            alert("您确定是上【" + department + classInfo + "】的课吗？") ;
        }
    </script>

------解决方案--------------------

jsp中：
HTML code
<tr>
    <td>区域 </td>
    <td>
        <select style="width: 155px" id="selectArea" name="issueTracking.areaCode" onchange="whenAreaChange();"></select>
        <s:textfield name="issueTracking.areaName" id="textAreaName" readonly="true" />
    </td>
</tr>
<tr>
    <td>製程</td>
    <td>
        <select style="width: 155px" id="selectProcess" name="issueTracking.process"></select>
        <s:textfield name="issueTracking.processName" id="textProcess" readonly="true" />
    </td>
</tr>