我正在使用一个简单的 jsp 根据输入参数（邮政编码）在 javascript 中使用 ajax 填充下拉框（以地址作为选项）。javascript 代码能够提取所需的数据，并在 select 元素中设置选项，但在几分之一秒之后，所有更改都消失了，jsp 又回到了初始状态。您能帮我解决此行为的原因吗？提前致谢。
主要 JSP 代码：testajx.jsp
<form name="testform" method="POST" action="testajx.jsp" >
<h1><%=a%> testing <b>Postcode Lookup</b></h1>
<br>
<br>
<input type="text" name="ziporpostalcode" size="10" maxlength="7" value="<%=ziporpostalcode%>"/>
<input type="text" name="ziporpostalcodetest" size="10" maxlength="7" value=""/>
<input type="hidden" name="searchPostCodeHidden" value="">
<input type="button" name="searchPostCode" value="Search" onclick="if(ziporpostalcode.value == ''){alert('enter postcode');}else {searchPostCodeHidden.value = 'TRUE'; this.form.submit();}">
<input type="hidden" name="searchAddressHidden" value="">
<input type="button" name="test" value="test" onclick="alert(userAddress.value);alert('<%=userAddress%>');">
<input type=image name="op_xxx" value="Search Address xxx" src="\jsp\htdocs\assets\images2011\buttons\search_address.gif" alt="Search Address" onclick="sendRequest('GET','testajax.jsp?ziporpostalcode='+ziporpostalcode.value)"href="#" />
<select name="userAddress" value="<%=userAddress%>" onchange="searchAddressHidden.value = userAddress.value; form.submit();">
<option>--- Select ---</option>
<%=addressOptions%>
</select>
<div id="ajax_res">a</div>
</body>
</form>
从 testajax.jsp 收到的结果：
<body>
<select name="userAddress">
<option>--- Select ---</option>
<%
String addressOptions = new String();
Picklist pl = new Picklist();
addressOptions = "";
String ziporpostalcode = request.getParameter("ziporpostalcode");
pl = PostcodeHandler.getAddressList(ziporpostalcode);
PicklistItem[] pli = pl.getItems();
//Iterator li = sAddressList.values().iterator();
for(int i=0; i<pl.getTotal(); i++)
{
addressOptions += "<option label=\""+pli[i].getPartialAddress()+"\" value=\""+pli[i].getMoniker()+"\">"+pli[i].getText()+"</option>";
session.setAttribute("addressOptions", addressOptions);
request.setAttribute("ziporpostalcode", ziporpostalcode);
request.setAttribute("searchPostCodeHidden", ziporpostalcode);
// addressOptions += "<option label='"+sAddressList.get(i).toString()+"' value='"+sAddressList.get(i).toString()+"'>"+sAddressList.get(i).toString()+"</option>";
}
String str="This is JSP string loading from JSP page in ajax, loading time :";
out.print(addressOptions);
%>
</select>
ajax javascript代码是：
<script language="Javascript" type="text/javascript">
function createRequestObject(){
var req;
try {
// Firefox, Opera, Safari
req = new XMLHttpRequest();
} catch (e) {
// Internet Explorer
try {
//For IE 6
req = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
//For IE 5
req = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {
alert('Your browser is not IE 5 or higher, or Firefox or Safari or Opera');
}
}
}
return req;
}
//Make the XMLHttpRequest Object
var http = createRequestObject();
function sendRequest(method, url){
if(method == 'get' || method == 'GET'){
http.open(method,url,true);
http.onreadystatechange = handleResponse;
http.send(null);
}
}
function handleResponse(){
if(http.readyState == 4 && http.status == 200){
var response = http.responseText;
if(response){
document.getElementById("ajax_res").innerHTML = response;
document.getElementById("ziporpostalcodetest").value = 'response';
document.getElementById("testform").action = 'testajax.jsp';
alert('received something from Ajax');
}
}
}