在我们Web应用系统开发当中，文件的上传和下载的功能是非常常用的功能。本文将为各位小伙伴讲解一下JavaWeb实现上传和下载文件功能的实例，详细内容如下。
第一步：导包
导入commons-fileupload-1.3.3.jar和commons-io-2.4.jar两个依赖包
第二步：编写前端页面
1、提交页面 index.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="${pageContext.request.contextPath }/fileUpload" method="post" enctype="multipart/form-data">
头像：<input type="file" name="img" accept="image/*"/>
<input type="submit" value="提交"/>
</form>
</body>
</html>2、结果页面 result.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<center>
<a href="${pageContext.request.contextPath }/download?filename=${filename}" >
<img alt="xx" src="https://atts.zijiebao.com/attachments/${src }">
</a>
</center>
</body>
</html>第三步：编写上传和下载代码
1、上传图片 fileUpload.java
package cn.yz123123.controller;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
@WebServlet("/fileUpload")
@MultipartConfig
public class fileUpload extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//String username = request.getParameter("username");
Part part = request.getPart("img");
//获取文件的真实名称
String header = part.getHeader("content-disposition");
String realName = header.substring(header.indexOf("filename=")+10, header.length()-1);
//获取文件自身流
InputStream inputStream = part.getInputStream();
//获取file真实路径，如果没有则创建
String dir = request.getServletContext().getRealPath("/file/");
File dirFile = new File(dir);
//上面只是实例化了一个对象，并没有真正的创建一个文件夹
if (!dirFile.exists()) {
dirFile.mkdirs();
}
//创建文件对象，并用流的形式写在相应的文件夹中
File file = new File(dir, realName);
FileOutputStream fileOutputStream = new FileOutputStream(file);
byte[] buf = new byte[1024];
int len;
while((len=inputStream.read(buf))!=-1) {
fileOutputStream.write(buf, 0, len);
}
fileOutputStream.close();
inputStream.close();
//以下为测试
request.setAttribute("src", request.getContextPath()+"/file/"+realName);
request.setAttribute("filename", realName);
request.getRequestDispatcher("/result.jsp").forward(request, response);
}
}2、下载图片 fileDownload.java
package cn.yz123123.controller;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(urlPatterns = "/download")
public class fileDownload extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String filename = req.getParameter("filename");
//获取文件的真实路径
String filePath = req.getServletContext().getRealPath("/file/"+filename);
FileInputStream fileInputStream = new FileInputStream(filePath);
resp.setCharacterEncoding("UTF-8");
resp.setHeader("Content-Disposition","attachment;filename="+UUID.randomUUID()+filename);
ServletOutputStream outputStream = resp.getOutputStream();
byte[] buf = new byte[1024];
int len;
while((len=fileInputStream.read(buf))!=-1) {
outputStream.write(buf, 0, len);
}
outputStream.close();
fileInputStream.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doGet(req, resp);
}
}以上就是关于JavaWeb实现上传和下载文件功能实例的全部内容，想要了解更多关于JavaWeb开发的详细内容，请关注W3Cschool，也希望大家多多支持。
