神奇的Ajax

<form name="form1" action="" method="post">
  用户名
  <input type="text" id="uname" name="username" value=""
    onblur="checkUserExists()" />
  <div id="mess" style="display: inline"/>    
</form>

function checkUserExists() {
  var f = document.form1;
  var username = f.username.value;
  if (username == "") {
  alert("用户名不能为空");
  return false;
  } else {
  doAjax("CheckUserServlet?username=" + username);
  }
}

var xmlhttp;
function doAjax(url) {
  try {
  xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
  } catch (e) {
  try {
    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
  } catch (e) {
    try {
    xmhttp = new XMLHttpRequest();
    if (xmlhttp.overrideMimeType) {
      xmlhttp.overrideMimeType("text/xml");
    }
    } catch (e) {   }
  }
  }
}

function processRequest() {
  var messdiv = document.getElementById(“mess”)；
  if (xmlhttp.readyState == 4)
  if (xmlhttp.status == 200) {
    //responseText表示请求完成后，返回的字符串信息    
            if (xmlhttp.responseText == "false")
    messdiv.innerHTML = "用户名可以使用";      
            else 
    messdiv.innerHTML = "用户名已被使用";    
        } else {
    alert("请求处理返回的数据有错误");    
  }
  }
}

function doAjax(){
  createXMLHttpRequest();
  var name = document.getElementById("uname").value;
  var pwd = document.getElementById("upwd").value;
  if(XMLHttp!=null){
  var url ="LoginServlet?uname="+name+"&upwd="+pwd； 
  XMLHttp.open("POST",url,true);
  XMLHttp.setRequestHeader("Content-Type",
    "application/x-www-form-urlencoded;");
  XMLHttp.onreadystatechange=processRequest;
  XMLHttp.send(null);
  }else{
  alert("不能创建XMLHttpRequest对象实例")
  }
}

public class SearchSuggest extends HttpServlet {
  public void doGet( …) { 
  … 
  String str = request.getParameter("search");
  List strList=new ArrayList();
  try{
    if(str!=null&str.length()>0){  
    …
    rs=stmt.executeQuery("select distinct(title) from 
      suggest where title like '"+str+"%' order by title");
    while(rs.next())
      strList.add(rs.getString("title"));         StringBuffer sbu=new StringBuffer();
    int size = strList.size();
    for(int i=0;i<size;i++)
      sbu.append((String)strList.get(i)+"-");
    out.print(sbu.toString());  
    }
  }catch(Exception e){  e.printStackTrace();  }
  }
}

function processReuqest(){
  if(xmlhttp.readyState==4){
       if(xmlhttp.status==200){
    var sobj=document.getElementById("suggest");
    sobj.innerHTML="";
    var str= xmlhttp.responseText.split("-");
    var suggest="";
    if(str.length>0&&str[0].length>0){
    for(i=0;i<str.length;i++){
      suggest+="<div onmouseover='javascript:suggestOver(this);'";
      suggest+=" onmouseout='javascript:suggestOut(this);'";
      suggest+=" onclick='javascript:setSearch(this.innerHTML);'";
      suggest+=" class='suggest_link'>"+str[i]+"</div>";
    }
    sobj.innerHTML=suggest;
    document.getElementById("suggest").style.display="block";
    }else{
    document.getElementById("suggest").style.display="none";
    }
       }
  }
}