Java Web实现资源上传以及下载

墨蓝 2022-05-08 16:54 178阅读 0赞

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:

![70][]

![70 1][]

![70 2][]

项目框架图:

![70 3][]

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][https_github.com_iunique_IdeaProject_tree_master_loadup]

[70]: /images/20220506/5c9055fac2524aeba71fb1dca33b596f.png
[70 1]: /images/20220506/a540a6d00f79466baf2c7d241f18e55f.png
[70 2]: /images/20220506/7d9a14d4136c43a49929166e7a550d1b.png
[70 3]: /images/20220506/5bf4e5c81d534d94a36e01c079c86992.png
[https_github.com_iunique_IdeaProject_tree_master_loadup]: https://github.com/iunique/IdeaProject/tree/master/loadup