主要是通过UploadListener 监听服务端接收了多少字节，返回给客户端，由javascript,div,css来操作进度条的显示
public class UploadListener implements OutputStreamListener
{
??? private HttpServletRequest request;
??? private long delay = 0;
??? private long startTime = 0;
??? private int totalToRead = 0;
??? private int totalBytesRead = 0;
??? private int totalFiles = -1;

??? public UploadListener(HttpServletRequest request, long debugDelay)
??? {
??????? this.request = request;
??????? this.delay = debugDelay;
??????? totalToRead = request.getContentLength();
??????? this.startTime = System.currentTimeMillis();
??? }

??? public void start()
??? {
??????? totalFiles ++;
??????? updateUploadInfo("start");
??? }

??? public void bytesRead(int bytesRead)
??? {
??????? totalBytesRead = totalBytesRead + bytesRead;
??????? updateUploadInfo("progress");

??????? try
??????? {
??????????? Thread.sleep(delay);
??????? }
??????? catch (InterruptedException e)
??????? {
??????????? e.printStackTrace();
??????? }
??? }

??? public void error(String message)
??? {
??????? updateUploadInfo("error");
??? }

??? public void done()
??? {
??????? updateUploadInfo("done");
??? }

??? private long getDelta()
??? {
??????? return (System.currentTimeMillis() - startTime) / 1000;
??? }

??? private void updateUploadInfo(String status)
??? {
??????? long delta = (System.currentTimeMillis() - startTime) / 1000;
??????? request.getSession().setAttribute("uploadInfo", new UploadInfo(totalFiles, totalToRead, totalBytesRead,delta,status));
??? }

}

上面的代码中，原作者为了演示本机操作上的显示效果，特别加入了debugDelay做延时处理，在实际应用中可以删除。

upload.jsp:
<%@ page import="be.telio.mediastore.ui.upload.MonitoredDiskFileItemFactory" %>
<%@ page import="be.telio.mediastore.ui.upload.UploadListener" %>
<%@ page import="org.apache.commons.fileupload.FileItem" %>
<%@ page import="org.apache.commons.fileupload.FileItemFactory" %>
<%@ page import="org.apache.commons.fileupload.FileUploadException" %>
<%@ page import="org.apache.commons.fileupload.servlet.ServletFileUpload" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%--
/* Licence:
*?? Use this however/wherever you like, just don't blame me if it breaks anything.
*
* Credit:
*?? If you're nice, you'll leave this bit:
*
*?? Class by Pierre-Alexandre Losson -- http://www.telio.be/blog
*?? email : plosson@users.sourceforge.net
*/
--%>
<%
??? UploadListener listener = new UploadListener(request, 30);

??? // Create a factory for disk-based file items
??? FileItemFactory factory = new MonitoredDiskFileItemFactory(listener);

??? // Create a new file upload handler
??? ServletFileUpload upload = new ServletFileUpload(factory);

??? try
??? {
??????? // process uploads ..
??????? upload.parseRequest(request);
//....处理上传文件
??? }
??? catch (FileUploadException e)
??? {
??????? e.printStackTrace();? //To change body of catch statement use File | Settings | File Templates.
??? }
%>