1．服务器端代码
服务器端代码主要实现依据客户端的请求信息，返回相应百分比数字。打开记事本，输入下列代码：
案例10-5
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<%!
int counter = 1;//注意：多用户将共享此变量，此进度条只适合单用户
%>
<%
String task = request.getParameter("task");
String res = "";
if (task.equals("create")) {
res = "1";
counter = 1;
}
else {
String percent = "";
switch (counter) {
case 1: percent = "10"; break;
case 2: percent = "23"; break;
case 3: percent = "35"; break;
case 4: percent = "51"; break;
case 5: percent = "64"; break;
case 6: percent = "73"; break;
case 7: percent = "89"; break;
case 8: percent = "100"; break;
}
counter++;
res = "<percent>" + percent + "</percent>";
}
response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
out.println("<response>");
out.println(res);
out.println("</response>");
out.close();
%>
将上述代码保存，名称为ProgressBarJsp.jsp。在该文件中，声明了一个变量counter，并赋值为1，该变 量是进度条返回百分比数字的依据。在下面使用request对象获取客户端传送的变量task的值，如果该值为“create”，表示需要重新创建进度 条，并设定counter的值为1。如果task不是create，则会依据counter的值返回百分比数字，完成一次操作，counter值加1。
2．客户端代码
本案例的客户端代码主要实现依据返回百分比数字显示进度条的状态。打开记事本，输入下列代码：
案例10-5
<html>
<head>
<title>JSP+Ajax 进度条</title>
<script type="text/javascript">
var xmlHttp;
var bar_color = 'blue';
var span_id = "yellow";
var clear = " "
function createXMLHttpRequest() {
if (window.ActiveXObject) {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
else if (window.XMLHttpRequest) {
xmlHttp = new XMLHttpRequest();
}
}
function go() {
createXMLHttpRequest();
checkDiv();
var url = "ProgressBarJsp.jsp?task=create";
xmlHttp.open("GET", url, true);
xmlHttp.onreadystatechange = goCallback;
xmlHttp.send(null);
}
function goCallback() {
if (xmlHttp.readyState == 4) {
if (xmlHttp.status == 200) {
setTimeout("pollServer()", 2000);
}
}
}
function pollServer() {
createXMLHttpRequest();
var url = "ProgressBarJsp.jsp?task=poll";
xmlHttp.open("GET", url, true);
xmlHttp.onreadystatechange = pollCallback;
xmlHttp.send(null);
}
function pollCallback() {
if (xmlHttp.readyState == 4) {
if (xmlHttp.status == 200) {
var percent_complete = xmlHttp.responseXML.getElementsByTagName("percent")[0].firstChild.data;
var index = processResult(percent_complete);
for (var i = 1; i <= index; i++) {
var elem = document.getElementById("block" + i);
elem.innerHTML = clear;
elem.style.backgroundColor = bar_color;
var next_cell = i + 1;
if (next_cell > index && next_cell <= 9) {
document.getElementById("block" + next_cell).innerHTML = percent_complete + "%";
}
}
if (index < 9) {
setTimeout("pollServer()", 2000);
} else {
document.getElementById("complete").innerHTML = "网站已完成加载!";
}
}
}
}
function processResult(percent_complete) {
var ind;
if (percent_complete.length == 1) {
ind = 1;
} else if (percent_complete.length == 2) {
ind = percent_complete.substring(0, 1);
} else {
ind = 9;
}
return ind;
}
function checkDiv() {
var progress_bar = document.getElementById("progressBar");
if (progress_bar.style.visibility == "visible") {
clearBar();
document.getElementById("complete").innerHTML = "";
} else {
progress_bar.style.visibility = "visible"
}
}
function clearBar() {
for (var i = 1; i < 10; i++) {
var elem = document.getElementById("block" + i);
elem.innerHTML = clear;
elem.style.backgroundColor = "white";
}
}
</script>
</head>
<body onload="go();">
<h1 align=center>网站正在加载中，请稍候</h1>
<p>
<table align="center">
<tbody>
<tr><td>
<div id="progressBar" style="padding:2px;border:solid yellow 2px;visibility:hidden">
<span id="block1"> </span>
<span id="block2"> </span>
<span id="block3"> </span>
<span id="block4"> </span>
<span id="block5"> </span>
<span id="block6"> </span>
<span id="block7"> </span>
<span id="block8"> </span>
<span id="block9"> </span>
</div>
</td></tr>
<tr><td align="center" id="complete"></td></tr>
</tbody>
</table>
</body>
</html>
------------------------以下是从跳转action的实例--------------