环境配置：导入依赖 jar 包。

• commons-fileupload-1.4.jar

  commons-io-2.6.jar

上传表单的enctype属性

enctype 属性规定在发送到服务器之前应该如何对表单数据进行编码。

语法

属性值

ServletFileUpload对象解析请求

ServletFileUpload类是Apache组件处理文件上传的核心高级类，通过使用parseRequest(HttpServletRequest)方法可以将HTML中每个表单提交的数据封装成个Fileltem对象，然后以List列表的形式返回。

ServletFileUpload类方法

ServletFileUpload详细简绍

FileItem接口常用方法

FileItemFactory 接口的常用方法

文件上传

① 表单数据提交方式：POST
② 表单提交数据的类型：...
③ 表单中设置文件上传项：

页面

<%@ page language="java" import="java.util.*" contentType="text/html; charset=UTF-8"%>





用户名:

<%--    加上multiple属性实现一次上次多个文件--%>选择文件:

servlet页面

package file;import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;/*** @author: BRILIANT屠一乐* @date: 2022/12/2 15:41* @description:*/@WebServlet(description = "FileUpload", urlPatterns = {"/FileUpload"})
public class FileUpload extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("UTF-8");response.setCharacterEncoding("UTF-8");response.setContentType("text/html");//enctype 属性是否是multipart/form-databoolean isMultipart = ServletFileUpload.isMultipartContent(request);//获取输出流PrintWriter writer = response.getWriter();//上传者String userName = "";//上传的文件名，最后输出用StringBuffer fileStr = new StringBuffer("");try {if (isMultipart) {//创建工厂实例FileItemFactory factory = new DiskFileItemFactory();//ServletFileUp-load实例依赖于FileItemFactory工厂ServletFileUpload upload = new ServletFileUpload(factory);//解析表单字段 封装成一个FileItem实例的集合List itemList = upload.parseRequest(request);//迭代器Iterator iterator = itemList.iterator();while (iterator.hasNext()) {//依次解析每一个FileItem实例，即表单FileItem fileItem = iterator.next();if (fileItem.isFormField()) {//普通表单字段//如果表单属性name的值的userName, 就获取这个表单字段的值if (fileItem.getFieldName().equals("userName")) {//getString方法：重载方法getString(String encoding），可指定所采用的编码集userName = fileItem.getString("UTF-8");}} else {//文件表单字段// getName()获得文件字段中所上传的文件名，普通表单字段调用此方法返回 nullString fileUpName = fileItem.getName();//用户上传的文件名File file = new File("E:\\idea_program\\Web\\file\\src\\main\\webapp\\temp\\" + fileUpName);//要保存到的文件if (!file.exists()) {
//                            file.createNewFile();//一开始肯定是没有的，所以先创建出来}fileItem.write(file);//写入，保存到目标文件fileStr.append(fileUpName + "、");}}fileStr.replace(fileStr.lastIndexOf("、"), fileStr.length(), "");writer.print("");}} catch (Exception e) {e.printStackTrace();}}
}

文件下载

jsp页面

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@page isELIgnored="false" %>





文件下载列表
">QQ图片20220704200735.jpg


">deity.rar


">maggie.rar


">rvncsse.rar

servlet页面

package sunyang; /*** @author: BRILIANT屠一乐* @date: 2022/12/3 19:39* @description:*/import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.*;@WebServlet("/Download")
public class Download extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("下载");System.out.println(request.getParameter("path"));String path = new String(request.getServletContext().getRealPath("1.png").getBytes("iso-8859-1"));File file = new File(path);InputStream in = new FileInputStream(file);//通过响应建立输出流OutputStream os = response.getOutputStream();response.addHeader("Content-Disposition", "attachment;filename=" + new String(file.getName().getBytes("gbk"), "iso-8859-1"));response.addHeader("Content-Length", String.valueOf(file.length()));response.setCharacterEncoding("utf-8");//通知浏览器以下载的方式打开response.setContentType("application/octet-stream");int data = 0;while ((data = in.read()) != -1) {os.write(data);}os.close();in.close();}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request,response);}
}

直接使用Servlet类和输入/输出流实现。与访问服务器文件不同的是，要实现文件的下载，不仅需要指定文件的路径，该需要在HTTP协议中设置两个响应消息头，如下

//设定接收程序处理数据的方式
Content-Disposition:attachment; filename =
//设定实体内容的MIME类型
Content-Type:application/x-msdownload