表单加Servlet实现文件的下载和上传

1.首页jsp 应该获取servlet请求转发过来的文件目录，显示文件名称，
注意：首先要进行逻辑判断，把list为空的情况筛选出来；
2.把转发来的list集合 展现在index页面中，在下载的超链接路径的参数传递文件名称，传到download的Servlet路径，然后在download的servlet的方法里面根据传来的名字，在资源目录里面找，如果存在该文件，则创建一个该文件的输入流进入内存，再通过response获得输出流，将输入流传到index页面
注意：
2.1应该设置传递的文件mime类型，resp.setContentType(contentType)，通过逻辑判断file的文件类型2.2如果浏览器获取到该流后，应该设置浏览器的打开方式，比如直接下载，就要设置http头信息，如果文件名称包含中文，就会报错，解决方法是：将文件名进行URL编码
String encodedFileName = URLEncoder.encode(submittedFileName, "UTF-8"); resp.setHeader("Content-Disposition","attachment;filename="+encodedFileName);        2.3 输出流最后应该flush ，输入流close关闭

3.文件上传 需要在表单里action里写上upload的servlet路径，然后在servlet里面接收传来的文件需要使用post请求，注意需要在servlet设置@MultipartConfig，

注意：先设置编码方式 再获取打印流

resp.setContentType("text/html;charset=UTF-8");
        PrintWriter writer = resp.getWriter();

4.servlet继承HttpServlet（）

import javax.servlet.http.HttpServlet;

前端页面的代码
<%@ page import="cn.hutool.core.util.ArrayUtil" %>
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>


    



文件列表

<%
    String[] list = (String[]) request.getAttribute("list");
%>
<%  if (ArrayUtil.isNotEmpty(list)){
    for (int i = 0; i
<%=list[i]%>   
下载



<%
    }
    }
%>

文件上传

    
    上传

index的Servlet

package fileupdown;

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.net.URLEncoder;

@WebServlet("/index")
public class Index extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        super.service(req, resp);
        //创建File对象，指向文件上传的目录
        File file = new File("D:\\CodeAll\\code\\FirstWeb\\src\\main\\webapp\\resourse");
        //获取该目录下的文件列表
        String[] list = file.list();
        req.setAttribute("list", list);
        req.getRequestDispatcher("index.jsp").forward(req, resp);

    }
}

upload的servlet

package fileupdown;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.*;

@WebServlet("/upload")
@MultipartConfig
public class FileUpload extends HttpServlet {
    @Override
    public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 获取文件部分
        Part part = req.getPart("file");
        //获取上传的文件名
        String submittedFileName = part.getSubmittedFileName();
        // 获取文件内容流
        InputStream fileContent = part.getInputStream();

        OutputStream outputStream = new
                FileOutputStream("D:\\CodeAll\\code\\FirstWeb\\src\\main\\webapp\\resourse\\"+submittedFileName);
        byte[] bytes = new byte[1024];
        int len = 0;
        while (-1!= (len =fileContent.read(bytes) )){
            outputStream.write(bytes,0,len);
        }
        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter writer = resp.getWriter();
        writer.print("");
        writer.print("");
        writer.print("
文件上传成功!
");
        writer.print("
3s后返回下载列表
");
        writer.print("");
        writer.print("");
        System.out.println("打印上传成功");

//        resp.setHeader("Refresh", "3; url=index.jsp");
        resp.setHeader("Refresh", "3; url=./index");
//        resp.sendRedirect("/index");
    }

}

download的servlet

package fileupdown;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.*;
import java.net.URLEncoder;

@WebServlet("/download")
@MultipartConfig
public class FileDownload extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        super.service(req, resp);
        //获取上传到服务器的文件名
        String submittedFileName = req.getParameter("name");
        File file = new File("D:\\CodeAll\\code\\FirstWeb\\src\\main\\webapp\\resourse\\" + submittedFileName);
        if (file.exists()){
            FileInputStream fileInputStream = new FileInputStream(file);
            String contentType = "";
            if (file.getName().endsWith(".jpg") || file.getName().endsWith(".jpeg")) {
                contentType = "image/jpeg";
            } else if (file.getName().endsWith(".png")) {
                contentType = "image/png";
            } else if (file.getName().endsWith(".gif")) {
                contentType = "image/gif";
            } else if (file.getName().endsWith(".pdf")) {
                contentType = "application/pdf";
            } else if (file.getName().endsWith(".doc") || file.getName().endsWith(".docx")) {
                contentType = "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
            } else if (file.getName().endsWith(".xls") || file.getName().endsWith(".xlsx")) {
                contentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
            } else if (file.getName().endsWith(".zip")) {
                contentType = "application/zip";
            } else if (file.getName().endsWith(".txt")) {
                contentType = "text/html;charset=UTF-8";
            } else if (file.getName().endsWith(".doc") || file.getName().endsWith(".docx")) {
                contentType = "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
            }
            resp.setContentType(contentType);
            // 对文件名进行URL编码
            String encodedFileName = URLEncoder.encode(submittedFileName, "UTF-8");
            resp.setHeader("Content-Disposition", "attachment; filename="+encodedFileName);
            ServletOutputStream outputStream = resp.getOutputStream();
            byte[] bytes = new byte[1024];
            int len = 0;
            while (-1!=(len=fileInputStream.read(bytes))){
                outputStream.write(bytes,0,len);
            }
            outputStream.flush();
            fileInputStream.close();
        }else {
            //进行文件不存在的处理
        }
    }
}