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="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 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"gt;
< taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" gt;
<!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="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<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！
