从服务器下载文件（附源码）

Lx灬星愿 06-22 277

前言：

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此篇是接上篇《文件上传服务器（附源码）》点击可跳转，均使用NIO。写的从服务器下载文件的Demo，均已测试可以运行，本人不太会写文章，可能因为头条的编辑器问题，无法有漂亮的排版，但是有详细的代码说明，粘贴即可使用。在此对文件上传及下载需要的jar做一个简单的总结：

文件上传的文章是使用的jsee目录结构，文件下载使用的是maven目录结构，只是对jar包的添加方式不同而已。网上有很多说明，在此不多说

需要jar包：commons-fileupload-1.3.2，commons-io-2.5，jstl-1.2

本项目是采用的maven目录结构，但是粘贴代码即可使用，请关注下文中涉及的目录

1.web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="" xmlns="" xsi:schemaLocation=" " version="2.5"> <display-name>efg</display-name> <welcome-file-list> <welcome-file>index.html</welcome-file> <welcome-file>index.htm</welcome-file> <welcome-file>index.jsp</welcome-file> <welcome-file>default.html</welcome-file> <welcome-file>default.htm</welcome-file> <welcome-file>default.jsp</welcome-file> </welcome-file-list>  <servlet> 	<servlet-name>fileUp</servlet-name> 	<servlet-class>com.abc.util.UploadHandleServlet2</servlet-class> </servlet>  <servlet-mapping> 	<servlet-name>fileUp</servlet-name> 	<url-pattern>/fileup.do</url-pattern> </servlet-mapping>  <servlet> 	<servlet-name>listFile</servlet-name> 	<servlet-class>com.abc.util.ListFileServlet</servlet-class> </servlet>  <servlet-mapping> 	<servlet-name>listFile</servlet-name> 	<url-pattern>/listFile.do</url-pattern> </servlet-mapping>  <servlet> 	<servlet-name>downLoadServlet</servlet-name> 	<servlet-class>com.abc.util.DownLoadServlet1</servlet-class> </servlet>  <servlet-mapping> 	<servlet-name>downLoadServlet</servlet-name> 	<url-pattern>/downLoadServlet.do</url-pattern> </servlet-mapping></web-app>

2.listfile.jsp 显示下载目录中

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%><%@ taglib prefix="c" uri="" %><!DOCTYPE html><html><head><meta charset="UTF-8"><title>文件下载</title></head><body>	<c:forEach var= "me" items="${fileMap }">		<c:url value="/downLoadServlet.do" var= "downurl">			<c:param name="filename" value="${me.key }"></c:param>		</c:url>		${me.value }:<a href="${downurl }">下载</a><br>	</c:forEach></body></html>

3.maven项目中pom.xml -导入项目jar包

<project xmlns=""	xmlns:xsi=""	xsi:schemaLocation=" ">	<modelVersion>4.0.0</modelVersion>	<groupId>com.abc</groupId>	<artifactId>efg</artifactId>	<version>0.0.1-SNAPSHOT</version>	<packaging>war</packaging>	<dependencies>		<dependency>			<groupId>commons-fileupload</groupId>			<artifactId>commons-fileupload</artifactId>			<version>1.3.2</version>		</dependency>		<dependency>			<groupId>commons-io</groupId>			<artifactId>commons-io</artifactId>			<version>2.5</version>		</dependency>		<dependency>			<groupId>javax.servlet</groupId>			<artifactId>jstl</artifactId>			<version>1.2</version>		</dependency>	</dependencies></project>

4.ListFileServlet -获取现在路径下的文件

package com.abc.util;import java.io.File;import java.io.IOException;import java.util.HashMap;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ListFileServlet extends HttpServlet {	/**	 * 	 */	private static final long serialVersionUID = 1L;	@Override	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		String uploadFilePath = this.getServletContext().getRealPath("/WEB-INF/upload");		Map<String, String> fileMap = new HashMap<String, String>();		File filePath = new File(uploadFilePath);		System.out.println(uploadFilePath);		if (!filePath.exists()) {			req.setAttribute("message", "文件为空！");			req.getRequestDispatcher("/WEB-INF/jsp/message.jsp").forward(req, resp);		} else {			fileList(filePath, fileMap);			req.setAttribute("fileMap", fileMap);			req.getRequestDispatcher("/WEB-INF/jsp/listfile.jsp").forward(req, resp);		}	}	private void fileList(File file, Map<String, String> fileMap) {		if(!file.isFile()) {			File[] files = file.listFiles();			for(File file2 : files) {				fileList(file2,fileMap);			}		}else {			System.out.println("===");			String realName = file.getName().substring(file.getName().lastIndexOf("_")+1);			System.out.println(realName);			System.out.println(file.getName().substring(file.getName().indexOf("_")+1));			System.out.println("===");			fileMap.put(file.getName(), realName);		}	}}

5.DownLoadServlet 文件下载工具类

package com.abc.util;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.OutputStream;import java.net.URLEncoder;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class DownLoadServlet extends HttpServlet {	/**	 * 	 */	private static final long serialVersionUID = 1L;	@Override	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {		req.setCharacterEncoding("utf-8");		resp.setCharacterEncoding("utf-8");		String fileName = req.getParameter("filename");		System.out.println(fileName);		String fileSaveRootPath = this.getServletContext().getRealPath("/WEB-INF/upload");		String realName = fileName.substring(fileName.indexOf("_") + 1);		String path = findFileSavePathByFileName(fileName, fileSaveRootPath);		File file = new File(path + File.separator + fileName);		if (!file.exists()) {			req.setAttribute("message", "您要下载的资源已被删除!");			req.getRequestDispatcher("/WEN-INF/jsp/message.jsp").forward(req, resp);			return;		}		resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(realName, "utf-8"));		FileInputStream in = new FileInputStream(path + File.separator + fileName);		OutputStream os = resp.getOutputStream();		byte[] buf = new byte[1024];		int len = 0;		while ((len = in.read(buf)) > 0) {			os.write(buf, 0, len);		}		in.close();		os.close();	}	private String findFileSavePathByFileName(String fileName, String fileSaveRootPath) {		int hashcode = fileName.hashCode();		int dir1 = hashcode & 0xf;		int dir2 = (hashcode & 0xf0) >> 4;		String dir = fileSaveRootPath + "\\" + dir1 + "\\" + dir2;		System.out.println(dir);		System.out.println(fileSaveRootPath + File.separator + dir1 + File.separator + dir2);		return dir;	}}文件上传与下载参照此两篇文章即可实现，至于细节各位可根据自己的项目进行调整，如有好的建议欢迎分享。本人将分享一些在工作项目中实际使用的工具类，烦请各位路过大佬提出改进建议。谢谢！

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