File upload and download demo

Reference tutorial ： The latest version of Silicon Valley JavaWeb A full set of tutorial ,java web Zero foundation entry full edition P213

One 、 Upload files

1.1 introduce jar package ：

• commons-fileupload-1.2.1.jar
• commons-io-1.4.jar

1.2 Programming

package com.atguigu.servlet;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
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.File;
import java.io.IOException;
import java.util.List;

/** * @author: sjmp1573 * @date: 2022/7/23 14:30 * @description: */

public class UploadServlet extends HttpServlet {
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        // 1. Judge whether the uploaded data is multi segment data , Only multi segment data is file upload .
        if (ServletFileUpload.isMultipartContent(req)) {
    
            // 2.  establish FileItemFactory  Factory implementation class , And create  ServletFileUpload  Easy to parse data and other operations .
            FileItemFactory fileItemFactory = new DiskFileItemFactory();
            ServletFileUpload fileUpload = new ServletFileUpload(fileItemFactory);
            try {
    
            // 3. Resolve request , get  FileItem  list 
                List<FileItem> list = fileUpload.parseRequest(req);
                // 4. Traverse  FileItem , Output data , Check whether the file is successful 
                for (FileItem fileItem :list) {
    
                    if (fileItem.isFormField()){
    
                        //  Common form items 
                        System.out.println(fileItem.getFieldName());
                        System.out.println(fileItem.getString("UTF-8"));
                    }else{
    
                        //  Uploaded file data , Write to disk 
                        fileItem.write(new File("E:\\"+fileItem.getName()));
                    }
                }
            } catch (Exception e) {
    
                e.printStackTrace();
            }
        }
    }
}

Remember in web.xml Middle configuration servlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0">
    <servlet>
        <servlet-name>UploadServlet</servlet-name>
        <servlet-class>com.atguigu.servlet.UploadServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>UploadServlet</servlet-name>
        <url-pattern>/uploadServlet</url-pattern>
    </servlet-mapping>
</web-app>

Two 、 File download

Put the downloaded file under the project path file Under the table of contents ：

Write file download program ：

package com.atguigu.servlet;

import org.apache.commons.io.IOUtils;

import javax.servlet.ServletContext;
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;
import java.io.IOException;
import java.io.InputStream;

/** * @author: sjmp1573 * @date: 2022/7/23 15:44 * @description: */

@WebServlet(name = "DownloadServlet", value = "/downloadServlet")
public class DownloadServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        System.out.println("hello");
        // 1. Get downloaded files , In a streaming way 
        String fileName = "d.jpg";
        ServletContext servletContext = getServletContext();
        InputStream resourceAsStream = servletContext.getResourceAsStream("/file/" + fileName);
        // 3. Set the returned data type 
        String mimeType = servletContext.getMimeType("/file/" + fileName);
        resp.setContentType(mimeType);
        // 4. Set the response header , Process content as a download 
        resp.setHeader("Content-Disposition", "attachment;" + "filename=" + fileName);
        // 2. Get the output stream of the response 
        ServletOutputStream outputStream = resp.getOutputStream();
        IOUtils.copy(resourceAsStream, outputStream);
    }
}