使用Common-FileUpload 1.2版本(20070103)。此版本提供了能够监视文件上传情况的 ProcessListener接口，
使开发者通过FileUploadBase类对象的setProcessListener方法植入自己的Listener。
FileUploadListener类实现了ProcessListener，在整个文件上传过程中，它对上传进度进行监控，
并且根据上传 情况实时的更新上传状态Bean。源代码如下：

/**
* 本例程演示了通过Web上传文件过程中的进度显示。您可以对本例程进行任何修改和使用。
*
* 如需要转载，请注明作者。
*
* 作者： 刘作晨
*
*/
package liuzuochen.sample.upload;

import org.apache.commons.fileupload.ProgressListener;
import javax.servlet.http.HttpServletRequest;

public class FileUploadListener implements ProgressListener{
private HttpServletRequest request=null;


public FileUploadListener(HttpServletRequest request){
this.request=request;
}

/**
* 更新状态
*/
public void update(long pBytesRead, long pContentLength, int pItems){
FileUploadStatus statusBean= BackGroundService.getStatusBean(request);
statusBean.setUploadTotalSize(pContentLength);
//读取完成
if (pContentLength == -1) {
statusBean.setStatus("完成对" + pItems +"个文件的读取:读取了 " + pBytesRead + " bytes.");
statusBean.setReadTotalSize(pBytesRead);
statusBean.setSuccessUploadFileCount(pItems);
statusBean.setProcessEndTime(System.currentTimeMillis());
statusBean.setProcessRunningTime(statusBean.getProcessEndTime());
//读取中
} else {
statusBean.setStatus("当前正在处理第" + pItems +"个文件:已经读取了 " + pBytesRead + " / " + pContentLength+ " bytes.");
statusBean.setReadTotalSize(pBytesRead);
statusBean.setCurrentUploadFileNum(pItems);
statusBean.setProcessRunningTime(System.currentTimeMillis());
}
BackGroundService.saveStatusBean(request,statusBean);
}
}

  2.1.3. 后台服务类（BackGroundService）

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　　 BackGroundService这个Servlet类负责接收Form Post数据、回应状态轮询请求、处理取消文件上传的请求。
尽管可以把这些功能相互分离开来，但为了简单明了，还是将它们放到Servlet中，只是由不同的方法进行分割。
源代码如下：

/**
* 本例程演示了通过Web上传文件过程中的进度显示。您可以对本例程进行任何修改和使用。
*
* 如需要转载，请注明作者。
*
* 作者： 刘作晨
*
*/
package liuzuochen.sample.upload;

import java.io.File;
import java.io.IOException;
import java.util.List;


import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.*;


public class BackGroundService extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet {

public static final String UPLOAD_DIR = "/upload";
public static final String DEFAULT_UPLOAD_FAILURE_URL = "./result.jsp";

public BackGroundService() {
super();
}


protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
/**
* 从文件路径中取出文件名
*/
private String takeOutFileName(String filePath) {
int pos = filePath.lastIndexOf(File.separator);
if (pos > 0) {
return filePath.substring(pos + 1);
} else {
return filePath;
}
}

/**
* 从request中取出FileUploadStatus Bean
*/
public static FileUploadStatus getStatusBean(
HttpServletRequest request) {
BeanControler beanCtrl = BeanControler.getInstance();
return beanCtrl.getUploadStatus(request.getRemoteAddr());
}
/**
* 把FileUploadStatus Bean保存到类控制器BeanControler
*/
public static void saveStatusBean( HttpServletRequest request, FileUploadStatus statusBean) {
statusBean.setUploadAddr(request.getRemoteAddr());
BeanControler beanCtrl = BeanControler.getInstance();
beanCtrl.setUploadStatus(statusBean);
}

/**
* 删除已经上传的文件
*/
private void deleteUploadedFile(HttpServletRequest request) {
FileUploadStatus satusBean = getStatusBean(request);
for (int i = 0; i < satusBean.getUploadFileUrlList().size(); i++) {
File uploadedFile = new File(request.getRealPath(UPLOAD_DIR) + File.separator + satusBean.getUploadFileUrlList(). get(i));
uploadedFile.delete();
}
satusBean.getUploadFileUrlList().clear();
satusBean.setStatus("删除已上传的文件");
saveStatusBean(request, satusBean);
}

/**
* 上传过程中出错处理
*/
private void uploadExceptionHandle( HttpServletRequest request, String errMsg) throws ServletException, IOException {
//首先删除已经上传的文件
deleteUploadedFile(request);
FileUploadStatus satusBean = getStatusBean(request);
satusBean.setStatus(errMsg);
saveStatusBean(request, satusBean);
}

/**
* 初始化文件上传状态Bean
*/
private FileUploadStatus initStatusBean(HttpServletRequest
request) {
FileUploadStatus satusBean = new FileUploadStatus();
satusBean.setStatus("正在准备处理");
satusBean.setUploadTotalSize(request.getContentLength());
satusBean.setProcessStartTime(System.currentTimeMillis());
satusBean.setBaseDir(request.getContextPath() + UPLOAD_DIR);
return satusBean;
}

/**
* 处理文件上传
*/
private void processFileUpload(HttpServletRequest request,

HttpServletResponse response) throws ServletException, IOException {
DiskFileItemFactory factory = new DiskFileItemFactory();
//设置内存缓冲区，超过后写入临时文件
factory.setSizeThreshold(10240000);
//设置临时文件存储位置
factory.setRepository(new File(request.getRealPath("/upload/temp")));
ServletFileUpload upload = new ServletFileUpload(factory);
//设置单个文件的最大上传值
upload.setFileSizeMax(102400000);
//设置整个request的最大值
upload.setSizeMax(102400000);
upload.setProgressListener(new FileUploadListener(request));
//保存初始化后的FileUploadStatus Bean
saveStatusBean(request, initStatusBean(request));

String forwardURL = "";
try {
List items = upload.parseRequest(request);
//获得返回url
for (int i = 0; i < items.size(); i++) {
FileItem item = (FileItem) items.get(i);
if (item.isFormField()) {
forwardURL = item.getString();
break;
}
}
//处理文件上传
for (int i = 0; i < items.size(); i++) {
FileItem item = (FileItem) items.get(i);

//取消上传
if (getStatusBean(request).getCancel()) {
deleteUploadedFile(request);
break;
}
//保存文件
else if (!item.isFormField() && item.getName().length() > 0) {
String fileName = takeOutFileName(item.getName());
File uploadedFile = new File(request.getRealPath(UPLOAD_DIR) +
File.separator + fileName); item.write(uploadedFile); //更新上传文件列表 FileUploadStatus
satusBean = getStatusBean(request);
satusBean.getUploadFileUrlList().add(fileName);
saveStatusBean(request, satusBean);
Thread.sleep(500);
}
}

} catch (FileUploadException e) {
uploadExceptionHandle(request, "上传文件时发生错误:" + e.getMessage());
} catch (Exception e) {
uploadExceptionHandle(request, "保存上传文件时发生错误:" + e.getMessage());
}
if (forwardURL.length() == 0) {
forwardURL = DEFAULT_UPLOAD_FAILURE_URL;
}
request.getRequestDispatcher(forwardURL).forward(request, response);
}

/**
* 回应上传状态查询
*/
private void responseStatusQuery(HttpServletRequest request,

HttpServletResponse response) throws IOException {
response.setContentType("text/xml");
response.setCharacterEncoding("UTF-8");
response.setHeader("Cache-Control", "no-cache");
FileUploadStatus satusBean = getStatusBean(request);
response.getWriter().write(satusBean.toJSon());
}

/**
* 处理取消文件上传
*/
private void processCancelFileUpload(HttpServletRequest request,

HttpServletResponse response) throws IOException {
FileUploadStatus satusBean = getStatusBean(request);
satusBean.setCancel(true);
saveStatusBean(request, satusBean);
responseStatusQuery(request, response);
}

protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
boolean isMultipart = ServletFileUpload.isMultipartContent(request);
if (isMultipart) {
processFileUpload(request, response);
} else {
request.setCharacterEncoding("UTF-8");

if (request.getParameter("uploadStatus") != null) {
responseStatusQuery(request, response);
}
if (request.getParameter("cancelUpload") != null) {
processCancelFileUpload(request, response);
}

}
}
}

  2.1.4. 文件上传状态控制类（BeanControler）

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