Javaweb项目中文件的上传与下载
文件上传：将本地文件通过流的方式上传到服务器，常用的文件上传方法有很多，本次主要介绍的文件上传技术是FileUpLoad.文件上传三要素：1、表单提交方式为post. 2、需要有属性,name元素和值。3、表单enctype="multipart/form-data"。文件下载：将服务器的文件通过流写到客户端。文件下载的方式主要为超链接下载和手动编写代码方式下载。
目录
1、文件上传入门
2-JS控制多个文件上传
3-防止上传重名文件覆盖问题
4-文件下载之超链接方式
5-文件下载之手动编写Servlet方式
6-文件下载之防止浏览器不同下载乱码问题
7-指定目录的文件下载案例
1、文件上传入门
首先创建web项目，配置tomcat服务器，导入文件上传所需jar包，具体如下：
web项目中创建文件上传的upload.jsp页面，具体如下：
<%--
Created by IntelliJ IDEA.
User: nuist__NJUPT
Date: 2022-08-15
Time: 16:53
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
Title
处理upload.jsp表单提交的Servlet类，具体如下：
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.List;
public class UploadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
boolean flag = ServletFileUpload.isMultipartContent(req) ;
if(!flag){
//如果表单不是enctype="multipart/form-data"
req.setAttribute("msg","表单设置不正确");
req.getRequestDispatcher("/jsp/upload.jsp").forward(req,resp);
}
try {
//1.创建磁盘文件项工厂
DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
diskFileItemFactory.setSizeThreshold(3*1024*1024); //设置缓冲区的大小为3MB
//设置文件的临时路径
String temp = getServletContext().getRealPath("/temp") ;
diskFileItemFactory.setRepository(new File(temp));
//2.创建一个核心解析类
ServletFileUpload fileUpload = new ServletFileUpload(diskFileItemFactory) ;
//设置上传文件的大小为5MB
// fileUpload.setSizeMax(5*1024*1024);
//3.利用核心类解析Request，解析后会得到多个部分,存入list集合中
List list = fileUpload.parseRequest(req) ;
//4.遍历文件项,判断文件项是普通项,还是文件上传项
for(FileItem fileItem : list){
if(fileItem.isFormField()){
//接收普通项的值
String name = fileItem.getFieldName() ;
String value = fileItem.getString("UTF-8") ;
System.out.println(name + " "+ value);
}else{
//文件上传项目
//获得文件上传项的文件名及文件内容
String filename = fileItem.getName() ;
int index = filename.lastIndexOf("\\") ;
if(index != -1){
//老版本浏览器
filename = filename.substring(index+1) ;
}
InputStream is = fileItem.getInputStream() ;
//获得文件上传的磁盘绝对路径
String realPath = getServletContext().getRealPath("/upload");
//创建一个输出流,写入到真实的路径中
OutputStream os = new FileOutputStream(realPath+"/"+filename) ;
//两个流实现对接
int len = 0 ;
byte [] bytes = new byte[1024] ;
while((len=is.read(bytes)) != -1){
os.write(bytes,0,len);
}
is.close();
os.close();
}
// fileItem.delete(); //删除临时文件
}
} catch (FileUploadException e) {
e.printStackTrace();
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
在web.xml文件中对使用的Servlet的名称及路径进行配置，具体如下：
UploadServlet
com.controller.UploadServlet
UploadServlet
/UploadServlet
2-JS控制多个文件上传
JavaScript控制多个文件上传，在原来的基础上，编写多文件上传页面jsp如下：
<%--
Created by IntelliJ IDEA.
User: nuist__NJUPT
Date: 2022-08-15
Time: 16:53
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
Title
多文件上传
3-防止上传重名文件覆盖问题
防止不同浏览器上传重名的文件将原始的文件覆盖掉，故使用工具类生成唯一的文件名，工具类如下：
import java.util.UUID;
/**
* 文件上传的工具类
*/
public class UploadUtils {
public static String getUuidFilename(String filename) {
//获得文件的扩展名
int index = filename.lastIndexOf(".");
String extension = filename.substring(index);
return UUID.randomUUID().toString().replace("-", "") + extension;
}
}
在servlet中使用该工具类对上传文件生成唯一的文件名，具体如下：
import com.utils.UploadUtils;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.List;
public class UploadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
boolean flag = ServletFileUpload.isMultipartContent(req) ;
if(!flag){
//如果表单不是enctype="multipart/form-data"
req.setAttribute("msg","表单设置不正确");
req.getRequestDispatcher("/jsp/upload.jsp").forward(req,resp);
}
try {
//1.创建磁盘文件项工厂
DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
diskFileItemFactory.setSizeThreshold(3*1024*1024); //设置缓冲区的大小为3MB
//设置文件的临时路径
String temp = getServletContext().getRealPath("/temp") ;
diskFileItemFactory.setRepository(new File(temp));
//2.创建一个核心解析类
ServletFileUpload fileUpload = new ServletFileUpload(diskFileItemFactory) ;
//设置上传文件的大小为5MB
// fileUpload.setSizeMax(5*1024*1024);
//3.利用核心类解析Request，解析后会得到多个部分,存入list集合中
List list = fileUpload.parseRequest(req) ;
//4.遍历文件项,判断文件项是普通项,还是文件上传项
for(FileItem fileItem : list){
if(fileItem.isFormField()){
//接收普通项的值
String name = fileItem.getFieldName() ;
String value = fileItem.getString("UTF-8") ;
System.out.println(name + " "+ value);
}else{
//文件上传项目
//获得文件上传项的文件名及文件内容
String filename = fileItem.getName() ;
int index = filename.lastIndexOf("\\") ;
if(index != -1){
//老版本浏览器
filename = filename.substring(index+1) ;
}
String filename1 = UploadUtils.getUuidFilename(filename) ;
InputStream is = fileItem.getInputStream() ;
//获得文件上传的磁盘绝对路径
String realPath = getServletContext().getRealPath("/upload");
//创建一个输出流,写入到真实的路径中
OutputStream os = new FileOutputStream(realPath+"/"+filename1) ;
//两个流实现对接
int len = 0 ;
byte [] bytes = new byte[1024] ;
while((len=is.read(bytes)) != -1){
os.write(bytes,0,len);
}
is.close();
os.close();
}
// fileItem.delete(); //删除临时文件
}
} catch (FileUploadException e) {
e.printStackTrace();
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
4-文件下载之超链接方式
文件下载方式1：超链接下载方式，下载服务器在download文件夹下的资源，代码如下：
<%--
Created by IntelliJ IDEA.
User: nuist__NJUPT
Date: 2022-08-15
Time: 20:22
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
Title
文件下载:超链接的方式
bootstrap.zip
a.docx
5-文件下载之手动编写Servlet方式
我们使用手动编写Servlet，将资源交给Servlet下载，首先在jsp页面将资源文件转给Servlet，代码如下：
<%--
Created by IntelliJ IDEA.
User: nuist__NJUPT
Date: 2022-08-15
Time: 20:22
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
Title
文件下载:手动编程下载的方式
bootstrap.zip
a.docx
然后编写用于处理文件下载的Servlet类，具体如下:
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class DownloadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//接收参数
String filename = request.getParameter("filename") ;
//下载，设置两个头和一个流
//设置Content-type
String type = request.getServletContext().getMimeType(filename) ;
response.setContentType(type);
//设置Content-Disposition
response.setHeader("Content-Disposition","attachment;filename="+filename);
//设置一个代表文件的输入流
String path = request.getServletContext().getRealPath("/download" ) ;
InputStream is = new FileInputStream(path+"/"+filename) ;
OutputStream os = response.getOutputStream() ;
//两个流的对接
int len = 0 ;
byte [] bytes = new byte[1024] ;
while((len=is.read(bytes)) != -1){
os.write(bytes,0,len);
}
is.close();
os.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
最后需要在web.xml文件中配置Servlet，具体如下：
DownloadServlet
com.controller.DownloadServlet
DownloadServlet
/DownloadServlet
6-文件下载之防止浏览器不同下载乱码问题
对于包含中文名称的文件，防止乱码，需要识别浏览器类型，并设置为UTF-8编码，具体的Servlet如下所示：
import com.utils.DownloadUtils;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLEncoder;
public class DownloadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//接收参数
String filename = new String(request.getParameter("filename").getBytes("ISO-8859-1"),"UTF-8");
//下载，设置两个头和一个流
//设置Content-type
String type = request.getServletContext().getMimeType(filename) ;
response.setContentType(type);
//设置一个代表文件的输入流
String path = request.getServletContext().getRealPath("/download" ) ;
File file = new File(path+"/"+filename);
// 判断浏览器的类型:
String agent = request.getHeader("User-Agent");
if(agent.contains("Firefox")){
// 使用的是Firefox
filename = DownloadUtils.base64EncodeFileName(filename);
}else{
// IE或者其他的浏览器
filename = URLEncoder.encode(filename, "UTF-8");
}
//设置Content-Disposition
response.setHeader("Content-Disposition","attachment;filename="+filename);
InputStream is = new FileInputStream(file) ;
OutputStream os = response.getOutputStream() ;
//两个流的对接
int len = 0 ;
byte [] bytes = new byte[1024] ;
while((len=is.read(bytes)) != -1){
os.write(bytes,0,len);
}
is.close();
os.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
当然这个servlet中对于火狐浏览器的编码问题使用了一个工具类，具体如下：
import java.io.UnsupportedEncodingException;
import sun.misc.BASE64Encoder;
public class DownloadUtils {
public static String base64EncodeFileName(String fileName) {
BASE64Encoder base64Encoder = new BASE64Encoder();
try {
return "=?UTF-8?B?"
+ new String(base64Encoder.encode(fileName
.getBytes("UTF-8"))) + "?=";
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
7-指定目录的文件下载案例
定义一个jsp页面用于在浏览器显示目录中的所有文件。
<%--
Created by IntelliJ IDEA.
User: nuist__NJUPT
Date: 2022-08-16
Time: 9:33
To change this template use File | Settings | File Templates.
--%>
<%@page import="java.io.File"%>
<%@page import="java.util.*"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
Insert title here
树形遍历
<%
// 1.创建一个队列：
Queue queue = new LinkedList();
// 2.先将跟节点入队：
File root = new File("E://resource");
queue.offer(root);
// 判断这个队列是否为空，不为空需要进行遍历:
while(!queue.isEmpty()){
// 将跟节点出队:
File file = queue.poll();
// 获得跟节点下的所有子节点:
File[] files = file.listFiles();
// 遍历所有子节点:
for(File f:files){
// 判断该节点是否为叶子节点:
if(f.isFile()){
%>
<%= f.getName() %>
<%
}else{
queue.offer(f);
}
}
}
%>
手动编写servlet处理文件下载问题，具体如下：
import com.utils.DownloadUtils;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLEncoder;
public class DownloadListServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 接收参数:
String path = request.getParameter("filename");
if(path != null){
path = new String(path.getBytes("ISO-8859-1"),"UTF-8");
}
File file = new File(path);
// 实现文件下载:设置两个头和一个流:
// 获得文件名
String filename = file.getName();
response.setContentType(getServletContext().getMimeType(filename));
// 设置另一个头：
String agent = request.getHeader("User-Agent");
if(agent.contains("Firefox")){
filename = DownloadUtils.base64EncodeFileName(filename);
}else{
filename = URLEncoder.encode(filename, "UTF-8");
filename = filename.replace("+", " ");
}
response.setHeader("Content-Disposition", "attachment;filename="+filename);
// 设置输入流:
InputStream is = new FileInputStream(file);
OutputStream os = response.getOutputStream();
int len = 0;
byte[] b = new byte[1024];
while((len = is.read(b))!=-1){
os.write(b, 0, len);
}
is.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
在web.xml中配置servlet，具体如下：
DownloadListServlet
com.controller.DownloadListServlet
DownloadListServlet
/DownloadListServlet