详解JavaWeb实现文件上传和下载的功能实例

2021-07-16 09:56:28 浏览数 (2308)

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.w3cschool.cn/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);
 }
}

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