ajax同步：req.open(‘get’,url,false);
實例：
js方法
var g_success =false;//全局變量
function getUser(username){
if("" == username){
alert("登錄名不能為空！");
return;
}
g_success = false;
var url = "<%=path%>/basicdata/gyshtyCheckUsername.do?mode=getUser&username="+encodeURI(encodeURI(username));
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
} elseif (window.ActiveXObject) {
req = new ActiveXObject("Microsoft.XMLHTTP");
}
if (req) {
req.open('get',url,false);//同步
req.setRequestHeader("Content-Length",username.length);
req.setRequestHeader("CONTENT-TYPE","application/x-www-form-urlencoded");
req.send("username="+encodeURI(encodeURI(username)));
if (req.readyState == 4){
if (req.status == 200){
result = req.responseText;
if('no.' == result){
alert("登錄名不存在！");
document.getElementById("username").value ="";
document.forms[0].username.focus();
}else{
g_success = true;
}
}
}
}
}
二、後臺服務類
String username = request.getParameter("username");
Users users = gyshtyService.findUsersByUsername(username);
String jsonStr="no";
if (users!=null) {
jsonStr = users.getUsername();
}else{
jsonStr = "no.";
}
response.setContentType("text/xml;charset=GBK");
response.setHeader("Cache-control","no-cache");
response.getWriter().print(jsonStr);
returnnull;
ajax異步：req.open(‘get’,url,true);
實例：
一、js方法
function getNext(){
if(window.XMLHttpRequest) {
req = new XMLHttpRequest();
} elseif(window.ActiveXObject) {
req = new ActiveXObject("Microsoft.XMLHTTP");
}
if(req) {
var url = “——”;
req.open("GET",url,true);
req.onreadystatechange = completeGetNext; //回調函數
req.send(null);
}
}
function completeGetNext(){
if(req.readyState == 1) {
document.getElementById("loadspan").innerHTML =
"<img src='../image/loading.gif' align='absmiddle'> <font color=red>數據加載中,請等待…</font>";
}
if(req.readyState == 4) {
if(req.status == 200) {
//取到結果之後，開始……
parseMessageNext();
}
}
}
二、後臺服務類
response.setContentType("text/xml;charset=GBK");
response.setHeader("Cache-control","no-cache");
String xml = "<?xml version=\"1.0\" encoding=\"GBK\" ?>";
/*
與數據庫交互，業務邏輯等
*/
response.getWriter().write(xml + str);
個人總結：在使用異步（true）時可以定義回調函數，在使用同步（false）時回調函數不能另定義一個回調函數名字。個人不知道原因所在，希望大傢告訴一下原因。
備註：以上代碼是開發中已經實現功能的代碼。