Ajax二级联动菜单

1、JavaScript

<script type="text/javascript">
	var xmlHttp;
	var result;
	function createXMLHttpRequest(){
		if(window.ActiveXObject){
			try{
				xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
			}catch(e1){
				try{
					xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
				}catch(e2){
					alert("创建XMLHttpRequest对象失败");
				}
			}
		}else if(window.XMLHttpRequest){
			xmlHttp=new XMLHttpRequest();
		}
	}
	function updates(){
		var selected=document.all.m.value;
		if(selected==""){
			while(document.all.s.options.length>0){
				document.all.s.removeChild(document.all.s.childNodes[0]);
			}
			var option=document.createElement("option");
			var defaults=document.all.defaults.value;
			option.text=defaults.split(",")[0];
			option.value=defaults.split(",")[1];
			document.all.s.options.add(option);
			return;
		}
		createXMLHttpRequest();
		xmlHttp.onreadystatechange=process;
		xmlHttp.open("get","testAction.do?m="+selected,true);
		xmlHttp.send(null);
	}
	function process(){
		if(xmlHttp.readyState==4){
			if(xmlHttp.status==200){
				result=xmlHttp.responseText;
				while(document.all.s.options.length>0){
					document.all.s.removeChild(document.all.s.childNodes[0]);
				}
				var results=result.split("/");
				for(var i=0;i<results.length;i++){
					var option=document.createElement("option");
					option.text=results[i].split(",")[0];
					option.value=results[i].split(",")[1];
					document.all.s.options.add(option);
				}
			}
		}
	}
</script>

 2、HTML

<select id="m" name="m" onChange="updates()">
   <option>
   <option value="1">
    a
   </option>
   <option value="2">
    b
   </option>
   <option value="3">
    c
   </option>
  </select>
  <select id="s" name="s">
   <option value="1">
    a
   </option>
  </select>
  <input type="hidden" name="defaults" value="a,1">

3、Action

	String s=request.getParameter("m");
	response.setContentType("text/html;charset=utf-8");
	PrintWriter out=response.getWriter();
	StringBuffer sb=new StringBuffer();
	if("1".equals(s)){
		sb.append("a,");
		sb.append("1/");
		sb.append("b,");
		sb.append("2/");
		sb.append("c,");
		sb.append("3");
		
	}else if("2".equals(s)){
		sb.append("aa,");
		sb.append("11/");
		sb.append("bb,");
		sb.append("22/");
		sb.append("cc,");
		sb.append("33");
	}else if("3".equals(s)){
		sb.append("aaa,");
		sb.append("111/");
		sb.append("bbb,");
		sb.append("222/");
		sb.append("ccc,");
		sb.append("333");
	}
	out.println(sb.toString());
	out.flush();
	out.close();
	return null;