借鉴别人的代码，自己再总结记录一下：

后台：

package com.sitech.easkLog;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.util.*;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import org.apache.commons.fileupload.FileItem;import org.apache.commons.fileupload.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.ServletFileUpload;/** * * @author administrator */@SuppressWarnings("unchecked")public class UpLoad extends HttpServlet {    /** */    private static final long serialVersionUID = 1L;    protected void processRequest(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        response.setContentType("text/html;charset=GBK");        String action = request.getParameter("action");        if("uploadFile".equals(action)){            this.uploadFile(request,response);  //上传文件        }    }    public void uploadFile(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        response.setContentType("text/html;charset=GBK");        request.setCharacterEncoding("GBK");        HttpSession session=request.getSession();        session.setAttribute("progressBar",0);      //定义指定上传进度的Session变量        String error = "";        int maxSize=50*1024*1024;        //单个上传文件大小的上限        DiskFileItemFactory factory = new DiskFileItemFactory();        //基于磁盘文件项目创建一个工厂对象        ServletFileUpload upload = new ServletFileUpload(factory);  //创建一个新的文件上传对象        try {            List items = upload.parseRequest(request);// 解析上传请求            Iterator itr = items.iterator();// 枚举方法            while (itr.hasNext()) {                FileItem item = (FileItem) itr.next();  //获取FileItem对象                if (!item.isFormField()) {
   // 判断是否为文件域                    if (item.getName() != null && !item.getName().equals("")) {
   // 判断是否选择了文件                        long upFileSize=item.getSize();     //上传文件的大小                        String fileName=item.getName();     //获取文件名                        //System.out.println("上传文件的大小:" + item.getSize());                        if(upFileSize>maxSize){                            error="您上传的文件太大，请选择不超过50M的文件";                            break;                        }                        // 此时文件暂存在服务器的内存中                        File tempFile = new File(fileName);// 构造临时对象                        String uploadPath = this.getServletContext().getRealPath("/upload");                        File file = new File(uploadPath,tempFile.getName());   // 获取根目录对应的真实物理路径                        InputStream is=item.getInputStream();                        int buffer=1024;     //定义缓冲区的大小                        int length=0;                        byte[] b=new byte[buffer];                        double percent=0;                        FileOutputStream fos=new FileOutputStream(file);                        while((length=is.read(b))!=-1){                            percent+=length/(double)upFileSize*100D;        //计算上传文件的百分比                            fos.write(b,0,length);                      //向文件输出流写读取的数据                            session.setAttribute("progressBar",Math.round(percent));    //将上传百分比保存到Session中                        }                        fos.close();                        Thread.sleep(1000);     //线程休眠1秒                    } else {                        error="没有选择上传文件！";                    }                }            }        } catch (Exception e) {            e.printStackTrace();            error = "上传文件出现错误：" + e.getMessage();        }        if (!"".equals(error)) {            request.setAttribute("error", error);            request.getRequestDispatcher("error.jsp").forward(request, response);        }else {            request.setAttribute("result", "文件上传成功！");            request.getRequestDispatcher("upFile_deal.jsp").forward(request, response);        }    }    @Override    protected void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException,            IOException {        processRequest(request, response);    }    @Override    protected void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException,            IOException {        processRequest(request, response);    }    @Override    public String getServletInfo() {        return "Short description";    }// }

上传jsp页面

<%@ page language="java" pageEncoding="UTF-8"%>          
     
         上传用户：
      
      
   上传文件1：
      
      
   上传文件2：
      
      
   
        
     
  

上传成功后：

<%@ page language="java" pageEncoding="UTF-8"%>           ${message}