Java Web实现资源上传以及下载

版权声明：欢迎转载，转载请注明原博客网址 https://blog.csdn.net/qq_37497322/article/details/83063684

为了方便导包，我用了maven创建项目，导包也是一样的，要导入的依赖如下:

<dependencies>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
      <scope>provided</scope>
    </dependency>
    <dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>1.3.3</version>
    </dependency>
    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>2.6</version>
    </dependency>
  </dependencies>

也就是要导入commons-fileupload和commons-io这两个包，我就简单得写了几个页面作为上传和下载的测试，测试效果如下:

项目框架图:

Upload.java：

package servlet;

import org.apache.commons.fileupload.FileItem;
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.List;

@WebServlet("/Upload")
public class Upload extends HttpServlet{
    private static final long serialVersionUID = 1L;

    // 上传文件存储目录
    private static final String UPLOAD_DIRECTORY = "upload";

    private static int index=0;

    // 上传配置
    private static final int MEMORY_THRESHOLD   = 1024 * 1024 * 3;  // 3MB
    private static final int MAX_FILE_SIZE      = 1024 * 1024 * 40; // 40MB
    private static final int MAX_REQUEST_SIZE   = 1024 * 1024 * 50; // 50MB

    /**
     * 上传数据及保存文件
     */
    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response) throws ServletException, IOException {
        // 检测是否为多媒体上传
        if (!ServletFileUpload.isMultipartContent(request)) {
            // 如果不是则停止
            PrintWriter writer = response.getWriter();
            writer.println("Error: 表单必须包含 enctype=multipart/form-data");
            writer.flush();
            return;
        }

        // 配置上传参数
        DiskFileItemFactory factory = new DiskFileItemFactory();
        // 设置内存临界值 - 超过后将产生临时文件并存储于临时目录中
        factory.setSizeThreshold(MEMORY_THRESHOLD);
        // 设置临时存储目录
        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));

        ServletFileUpload upload = new ServletFileUpload(factory);

        // 设置最大文件上传值
        upload.setFileSizeMax(MAX_FILE_SIZE);

        // 设置最大请求值 (包含文件和表单数据)
        upload.setSizeMax(MAX_REQUEST_SIZE);

        // 中文处理
        upload.setHeaderEncoding("UTF-8");

        // 构造临时路径来存储上传的文件
        // 这个路径相对当前应用的目录
        String uploadPath =this.getServletContext().getRealPath("/WEB-INF/upload");
        // 如果目录不存在则创建
        File uploadDir = new File(uploadPath);
        if (!uploadDir.exists()) {
            uploadDir.mkdir();
        }

        try {
            // 解析请求的内容提取文件数据
            @SuppressWarnings("unchecked")
            List<FileItem> formItems = upload.parseRequest(request);

            if (formItems != null && formItems.size() > 0) {
                // 迭代表单数据
                for (FileItem item : formItems) {
                    // 处理不在表单中的字段
                    if (!item.isFormField()) {
                        String fileName = new File(item.getName()).getName();
                        String filePath = uploadPath +File.separator + index+"_"+fileName;//为避免文件覆盖，设置一个静态的index，每次++作为前缀
                        index++;
                        File storeFile = new File(filePath);
                        // 在控制台输出文件的上传路径
                        System.out.println(filePath);
                        // 保存文件到硬盘
                        item.write(storeFile);
                        request.setAttribute("message",
                                "文件上传成功!");
                    }
                }
            }
        } catch (Exception ex) {
            request.setAttribute("message",
                    "错误信息: " + ex.getMessage());
        }
        // 跳转到 message.jsp
        getServletContext().getRequestDispatcher("/message.jsp").forward(
                request, response);
    }
}

ShowFiles.java:

package servlet;

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.*;
import java.util.HashMap;
import java.util.Map;

@WebServlet("/ShowFiles")
public class ShowFiles extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //获取上传文件的目录
        String uploadFilePath = this.getServletContext().getRealPath("/WEB-INF/upload");
        //存储要下载的文件名
        Map<String,String> fileNameMap = new HashMap<String,String>();
        //递归遍历filepath目录下的所有文件和目录，将文件的文件名存储到map集合中
        listfile(new File(uploadFilePath),fileNameMap);//File既可以代表一个文件也可以代表一个目录
        //将Map集合发送到download.jsp页面进行显示
        request.setAttribute("fileNameMap", fileNameMap);
        request.getRequestDispatcher("/download.jsp").forward(request, response);
    }
    public void listfile(File file,Map<String,String> map){
        //如果file代表的不是一个文件，而是一个目录
        if(!file.isFile()){
            //列出该目录下的所有文件和目录
            File files[] = file.listFiles();
            //遍历files[]数组
            for(File f : files){
                //递归
                listfile(f,map);
            }
        }else{
            String realName = file.getName().substring(file.getName().indexOf("_")+1);//将加入的前缀去掉获得原始的文件名
            //file.getName()得到的是文件的原始名称，这个名称是唯一的，因此可以作为key，realName是处理过后的名称
            map.put(file.getName(), realName);
        }
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

Download.java：

package servlet;

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.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URLEncoder;

@WebServlet("/Download")
public class Download extends HttpServlet
{

public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        //得到要下载的文件名
        String fileName = request.getParameter("filename");
        fileName = new String(fileName.getBytes("iso8859-1"),"UTF-8");
        //上传的文件都是保存在/WEB-INF/upload目录下的子目录当中
        String fileSaveRootPath=this.getServletContext().getRealPath("/WEB-INF/upload");
        //得到要下载的文件
        File file = new File(fileSaveRootPath + "\\" + fileName);
        //如果文件不存在
        if(!file.exists()){
        request.setAttribute("message", "您要下载的资源已被删除！！");
        request.getRequestDispatcher("/message.jsp").forward(request, response);
        return;
        }
        //处理文件名
        String realname = fileName.substring(fileName.indexOf("_")+1);
        //设置响应头，控制浏览器下载该文件
        response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(realname, "UTF-8"));
        //读取要下载的文件，保存到文件输入流
        FileInputStream in = new FileInputStream(fileSaveRootPath + "\\" + fileName);
        //创建输出流
        OutputStream out = response.getOutputStream();
        //创建缓冲区
        byte buffer[] = new byte[1024];
        int len = 0;
        //循环将输入流中的内容读取到缓冲区当中
        while((len=in.read(buffer))>0){
        //输出缓冲区的内容到浏览器，实现文件下载
        out.write(buffer, 0, len);
        }
        //关闭文件输入流
        in.close();
        //关闭输出流
        out.close();
        }

public void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        doGet(request, response);
        }
}

upload.jsp：

<%--
  Created by IntelliJ IDEA.
  User: hjy
  Date: 2018/10/14
  Time: 18:22
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>文件上传</title>
</head>
<body>
    <form method="post" action="/Upload" enctype="multipart/form-data">
        <span>选择一个文件</span>
        <input type="file" name="file"/>
        <br/><br/>
        <input type="submit" value="上传"/>
    </form>
</body>
</html>

message.jsp：

<%@ page import="java.util.List" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8" isELIgnored="false" import="servlet.ShowFiles" %>
<%@ page isELIgnored="false" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>文件上传结果</title>
</head>
<body>
<center>
    <h2>${message}</h2>
    <a href="/ShowFiles">进入下载页面</a>
</center>
</body>
</html>

download.jsp：

<%@ page import="java.util.HashMap" %>
<%@ page import="java.util.Map" %><%--
  Created by IntelliJ IDEA.
  User: hjy
  Date: 2018/10/15
  Time: 12:59
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>文件下载</title>
</head>
<body>
<%
    HashMap<String,String>map=(HashMap<String, String>) request.getAttribute("fileNameMap");
    for(Map.Entry<String,String>entry:map.entrySet())
    {
%>
    <form method="post" action="/Download">
        <span><%=entry.getValue()%></span>
        <input name="filename" style="display: none" value="<%=entry.getKey()%>"/>
        <input type="submit" value="下载"/>
    </form>
<%
    }
%>
</body>
</html>

虽然这个程序看起来很简单。。因为路径问题我调了好久，简直要吐血，get了一个新技能，以后写项目可能会用到

最后上传的文件会在target中

github原码:https://github.com/iunique/IdeaProject/tree/master/loadup