JavaWeb实现文件下载

1. 编写文件上传Servlet

 public class FileUpload1 extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

         InputStream in = null;
         OutputStream out = null;

         // 获取上传文件目录
         String savePath = this.getServletContext().getRealPath("/WEB-INF/upload");

         try {
             // 使用默认配置创建解析器工厂
             DiskFileItemFactory factory = new DiskFileItemFactory();
             // 获取解析器
             ServletFileUpload upload = new ServletFileUpload(factory);
             upload.setProgressListener(new ProgressListener() {
                 @Override
                 public void update(long l, long l1, int i) {
                     System.out.println("文件大小为：" + l1 + ",当前已处理：" + l);
                 }
             });
             // 解决上传文件名的中文乱码问题
             upload.setHeaderEncoding("UTF-8");
             // 上传表单是否为multipart/form-data类型
             if (!upload.isMultipartContent(request)) {
                 return;
             }
             // 解析request的输入流
             List<FileItem> fileItemList = upload.parseRequest(request);
             // 迭代list集合
             for (FileItem fileItem : fileItemList) {
                 if (fileItem.isFormField()) {
                     // 普通字段
                     String name = fileItem.getFieldName();
                     // 调用getString重载方法, 解决上传数据的中文乱码问题
                     String value = fileItem.getString("UTF-8");
                     System.out.println(name + "=" + value);
                 } else {
                     // 上传文件
                     // 获取上传文件名
                     String fileName = fileItem.getName();
                     // input:file没有指定上传文件时, 结束本次循环并继续下一次循环
                     if(fileName == null && fileName.trim().equals("")) {
                         continue;
                     }
                     fileName = fileName.substring(fileName.lastIndexOf("\\")+1);
                     // 使用UUID作为上传文件的名称
                     fileName = makeFileName(fileName);
                     // 获取输入流
                     in = fileItem.getInputStream();

                     // 上传文件名若不存在, 则先创建
                     File savePathDir = new File(savePath);
                     if (!savePathDir.exists()) {
                         savePathDir.mkdir();
                     }

                     // 使用hash算法产生当前上传图片的随机目录
                     String currentFileSavePath = makePath(savePath, fileName);

                     // 获取输出流
                     out = new FileOutputStream(currentFileSavePath + "\\" + fileName);
                     int len = 0;
                     byte[] buffer = new byte[1024];
                     while((len=in.read(buffer)) > 0) {
                         out.write(buffer, 0, len);
                     }
                 }
             }
         } catch (Exception e) {
             e.printStackTrace();
         } finally {
             if (in != null) {
                 in.close();
             }
             if (out != null) {
                 out.close();
             }
         }

     }
     public String makeFileName(String fileName) {
         return UUID.randomUUID().toString() + "_" + fileName;
     }
     public String makePath(String savePath, String fileName) {
         // 根据文件名产生int型hashcode, 32位二进制
         int hashcode = fileName.hashCode();
         // 获取第4位 0-15
         int dir1 = hashcode&0xf;
         // 获取第5-8位 0-15
         int dir2 = (hashcode&0xf0)>>4;
         // 凭借随机目录
         String dir = savePath + "\\" + dir1 + "\\" + dir2;  // upload\2\4
         // 若目录不存在时, 创建目录
         File file = new File(dir);
         if(!file.exists()) {
             file.mkdirs();
         }
         return dir;
     }

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
     }
 }

2. 编写获取所有下载文件名称Servlet

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/8/26 16:26
  * @Title:
  * @Description: 列出网站所有下载文件
  */
 public class ListFileServlet extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

         // 获取下载目录路径
         String filePath = this.getServletContext().getRealPath("/WEB-INF/upload");
         // 创建存储文件下载路径的Map集合
         Map filePathMap = new HashMap();
         // 将下载目录中所有文件名称存储到Map集合中
         listFile(new File(filePath), filePathMap);
         // 存储数据后跳转
         request.setAttribute("map", filePathMap);
         request.getRequestDispatcher("/listfile.jsp").forward(request, response);
     }

     /**
      * 将下载目录中所有文件名称存储到Map集合中
      * @param file 下载目录
      * @param filePathMap Map集合
      */
     private void listFile(File file, Map filePathMap) {
         if(!file.isFile()) {
             // 文件为目录时
             File[] files = file.listFiles();
             for (File f : files) {
                 // 递归调用
                 listFile(f, filePathMap);
             }
         } else {
             // 9349249849-88343-8344_阿_凡_达.avi 处理结果为: 阿_凡_达.avi
             String realName = file.getName().substring(file.getName().indexOf("_")+1);
             // 9349249849-88343-8344_阿_凡_达.avi -> 阿_凡_达.avi
             filePathMap.put(file.getName(), realName);
         }
     }

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
     }
 }

3. 处理文件下载请求Servlet

 public class FileDownload extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

         // 获取下载文件名称的key
         String filename = request.getParameter("filename");  //23239283-92489-dfsd_阿凡达.avi
         // 解决get请求的中文乱码问题
         filename = new String(filename.getBytes("iso8859-1"),"UTF-8");
         // 获取下载目录
         String path = makePath(filename,this.getServletContext().getRealPath("/WEB-INF/upload"));
         // 获取下载文件
         File file = new File(path + "\\" + filename);
         // 下载文件不存在时
         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;
         }
         // 获取下载文件名称 阿凡达.avi
         String realname = filename.substring(filename.indexOf("_") + 1);
         // 通知浏览器以下载方式打开, 不同浏览器可能不同
         response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(realname, "UTF-8"));
         // 下载文件
         FileInputStream in = new FileInputStream(path + "\\" + filename);
         OutputStream out = response.getOutputStream();
         byte buffer[] = new byte[1024];
         int len = 0;
         while((len=in.read(buffer))>0){
             out.write(buffer, 0, len);
         }
         in.close();
         out.close();

     }

     /**
      * 根据文件名称产生随机目录并将下载路径与随机目录拼接
      * @param filename 文件名称
      * @param savePath 下载路径
      * @return 下载路径与随机目录拼接结果
      */
     private String makePath(String filename,String savePath){

         int hashcode = filename.hashCode();
         int dir1 = hashcode&0xf;  //0--15
         int dir2 = (hashcode&0xf0)>>4;  //0-15

         String dir = savePath + "\\" + dir1 + "\\" + dir2;  //upload\2\3  upload\3\5
         File file = new File(dir);
         if(!file.exists()){
             file.mkdirs();
         }
         return dir;
     }

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doGet(req, resp);
     }
 }

4. 配置web.xml

 <!-- 文件上传 -->
 <servlet>
     <servlet-name>FileUpload1</servlet-name>
     <servlet-class>fileupload.FileUpload1</servlet-class>
 </servlet>
 <servlet-mapping>
     <servlet-name>FileUpload1</servlet-name>
     <url-pattern>/servlet/FileUpload1</url-pattern>
 </servlet-mapping>

 <!--文件下载-->
 <servlet>
     <servlet-name>ListFileServlet</servlet-name>
     <servlet-class>fileupload.ListFileServlet</servlet-class>
 </servlet>
 <servlet-mapping>
     <servlet-name>ListFileServlet</servlet-name>
     <url-pattern>/servlet/ListFileServlet</url-pattern>
 </servlet-mapping>
 <servlet>
     <servlet-name>FileDownload</servlet-name>
     <servlet-class>fileupload.FileDownload</servlet-class>
 </servlet>
 <servlet-mapping>
     <servlet-name>FileDownload</servlet-name>
     <url-pattern>/servlet/FileDownload</url-pattern>
 </servlet-mapping>

5. 编写获取文件名称JSP

 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 <%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 <html>
   <head>
     <title>My JSP 'listfile.jsp' starting page</title>
   </head>

   <body>

     <c:forEach var="me" items="${map}">
         <c:url value="/servlet/FileDownload" var="downurl">
             <c:param name="filename" value="${me.key}"></c:param>
         </c:url>
         ${me.value }  <a href="${downurl}">下载</a>  <br/>
     </c:forEach>

   </body>
 </html>

注意:

URL地址栏 -> 非ASCII码字符 -> URL编码
使用c:url传递中文数据

6. 编写文件上传JSP

 <%@ page contentType="text/html;charset=UTF-8" language="java" %>
 <html>
 <head>
     <title>演示文件上传</title>
 </head>
 <body>
     <form action="${pageContext.request.contextPath}/servlet/FileUpload1" method="post" enctype="multipart/form-data">
         用户名: <input type="text" name="username"/><br/>
         文件1: <input type="file" name="file1"/><br/>
         文件2: <input type="file" name="file1"/><br/>
         <input type="submit"/>
     </form>
 </body>
 </html>

7. 效果演示

在浏览器中访问http://localhost:8080/servlet/ListFileServlet