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;  // upload24
        // 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;  //upload23  upload35
        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