利用servlet怎么实现一个文件上传功能

package com.learn;

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.ServletFileUpload;
import org.apache.poi.common.usermodel.LineStyle;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;


public class ServletUpload extends HttpServlet {

  private String filePath;
  private String tempFilePath;
  @Override
  public void init(ServletConfig config) throws ServletException {
    super.init(config);
    //获取类文件路径初始化值
    filePath = config.getInitParameter("filePath");
    tempFilePath = config.getInitParameter("tempFilePath");
    System.out.println("init filepath:"+filePath);
    System.out.println("tempFilePath:"+tempFilePath);

    //获取文件路径真实值
    filePath = config.getServletContext().getRealPath(filePath);
    tempFilePath = config.getServletContext().getRealPath(tempFilePath);
    System.out.println("realPath:"+filePath);
    System.out.println("tempFilePath"+tempFilePath);


  }


  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    super.doPost(req, resp);
    //设置返回内容为纯文字内容
    resp.setContentType("text/plain");
    resp.setCharacterEncoding("UTF-8");
    //获取输出对象
    PrintWriter out = resp.getWriter();

    //创建一个基于硬盘的FileItem工厂
    DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
    //设置向硬盘写数据的缓冲区大小，这里为4k
    diskFileItemFactory.setSizeThreshold(4*1024);
    //设置临时目录
    diskFileItemFactory.setRepository(new File(tempFilePath));

    //创建一个文件上传处理器
    ServletFileUpload servletFileUpload = new ServletFileUpload(diskFileItemFactory);
    //设置文件上传的大小
    servletFileUpload.setSizeMax(4*1024*1024);
    //获取参数
    try {
      //获取表单参数
      List list = servletFileUpload.parseRequest(req);
      //获取迭代器
      Iterator iterator = list.iterator();
      //迭代列表
      while(iterator.hasNext()){

        //将参数转型为FileItem类型
        FileItem fileItem = (FileItem) iterator.next();
        if(fileItem.isFormField()){
          System.out.println("处理表单非文件类型数据");
          processFormFiled(fileItem,out);
        } else {
          System.out.println("处理吧表单文件类型数据");
          processUploadFile( fileItem,out);
        }

      }
      System.out.println("关闭输出流");
      out.close();

    } catch (FileUploadException e) {
      e.printStackTrace();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  private void processFormFiled(FileItem fileItem,PrintWriter printWriter){
    //获取表单域的名称
    String name = fileItem.getName();
    //获取表单域的值
    String value = fileItem.getString();
    printWriter.print("name:"+name+"value:"+value);

  }

  private void processUploadFile(FileItem fileItem,PrintWriter printWriter) throws Exception {

    //获取文件名称
    String fileName = fileItem.getName();
    int i = fileName.lastIndexOf("\\");
    fileName = fileName.substring(i+1,fileName.length());
    //获取文件大小
    long fileSize = fileItem.getSize();
    System.out.println("fileName:"+fileName+"| fileSize:"+fileSize);
    if("".equals(fileName) && fileSize == 0)
      return;
    //将文件写入指定位置
    File upload = new File(filePath+File.separator+fileName);
    fileItem.write(upload);
    //输出结果
    printWriter.print(fileName+"is saved");
    System.out.println("处理完毕");
    printWriter.print("the size of "+fileName+" is "+fileSize);
  }
}

  
    upload
    com.learn.ServletUpload
    
      filePath
      file
    
    
      tempFilePath
      temp
    
  
  
    upload
    /upload