在最近的一个项目中，有一个上传功能：上传一个cvs文件，然后解析此文件并写入数据库

由于经常需要传很大的文件，客户完成此功能往往需要40分钟，在这个过程中，页面也没有任何提示，用户体验非常不好？

为何不用ajax作一个进度条呢？

分两步完成此需求：

一：写一个简单的ajax，实现最简单的进度条功能。

二：把此进度条改造为项目可用的进度条。

一：最简单的进度条

1。客户端每2秒发送一个createXMLHttpRequest请求给服务端.并得到服务端返回的进度数据.根据服务端返回的数据,用Javascript 更新一个table的width,

这样就模拟了一个进度条.

progressBar.html.内容如下：

Ajax Progress Bar

var xmlHttp;

var key;

function createXMLHttpRequest() {

if (window.ActiveXObject) {

xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");

}

else if (window.XMLHttpRequest) {

xmlHttp = new XMLHttpRequest();

}

}

function go() {

createXMLHttpRequest();

clearBar();

var url = "ProgressBarServlet?task=create";

var button = document.getElementById("go");

button.disabled = true;

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 = "ProgressBarServlet?task=poll&key=" + key;

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 progress = document.getElementById("progress");

var progressPersent = document.getElementById("progressPersent");

progress.width = percent_complete + "%";

progressPersent.innerHTML = percent_complete + "%";

if (percent_complete < 100) {

setTimeout("pollServer()", 2000);

} else {

document.getElementById("complete").innerHTML = "Complete!";

//document.getElementById("go").disabled = false;

}

}

}

}

function clearBar() {

var progress_bar = document.getElementById("progressBar");

var progressPersent = document.getElementById("progressPersent");

var complete = document.getElementById("complete");

progress_bar.style.visibility = "visible"

progressPersent.innerHTML = " ";

complete.innerHTML = "Begin to upload this file...";

}

2：一个模拟servlet：ProgressBarServlet.java，内容如下：

package com.cyberobject.lcl.ajax;

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

/**

*

* @author nate

* @version

*/

public class ProgressBarServlet extends HttpServlet {

private int counter = 1;

/** Handles the HTTP GET method.

* @param request servlet request

* @param response servlet response

*/

protected void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

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 + "";

}

PrintWriter out = response.getWriter();

response.setContentType("text/xml");

response.setHeader("Cache-Control", "no-cache");

out.println("");

out.println(res);

out.println("");

out.close();

}

/** Handles the HTTP POST method.

* @param request servlet request

* @param response servlet response

*/

protected void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

doGet(request, response);

}

/** Returns a short description of the servlet.

*/

public String getServletInfo() {

return "Short description";

}

}

3：在web。xml中配置好servlet映射：

ProgressBarServlet

ProgressBarServlet

com.cyberobject.lcl.ajax.ProgressBarServlet

ProgressBarServlet

/ProgressBarServlet

此时进度条已经可以运行了。接下来的工作就是把它移植到我们的系统。

二：

1：在写数据库的class DbOperater中，增加一个progress属性

private int progress;

2:在写数据库的class中，增加一个getProgress()方法:

public int getProgress()

{

return progress;

}

3: 在写库的for循环中, progress++;

4:在调用DbOperater的servlet中调用DbOperater的getProgress()方法,这样就为进度条提供了实时数据.

5:另外:servlet的doGet()用来获得进度数据,doPost()用来上传文件和写库操作.彼此分工明确.

特此存档.