Давайте Разработаем сервис загрузки файлов С нуля, используя Java и Spring Boot

package com.webtutsplus.ecommerce.controller;

import com.webtutsplus.ecommerce.model.FileInfo;
import com.webtutsplus.ecommerce.service.FIleStoreService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder;

import java.io.IOException;
import java.nio.file.Path;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

@RestController
@RequestMapping("/fileUpload")
public class FileUploadController {

    @Autowired
    FIleStoreService fileStoreService;

    //upload a file
    @PostMapping("/")
    public String handleFileUpload(@RequestParam("file") MultipartFile file) {
        return fileStoreService.store(file);
    }


    // get all the files
    @GetMapping("/")
    public ResponseEntity> getListFiles() {
        
        // first get a stream of all file path present in root file directory
        Stream pathStream =  fileStoreService.loadAll();
        
        List fileInfos = pathStream.map(path -> {
            // get file name
            String filename = path.getFileName().toString();
            
            // use function to get one file to build the URL 
            String url = MvcUriComponentsBuilder
                    .fromMethodName(FileUploadController.class, "getFile", path.getFileName().toString()).build().toString();
            // make a fileinfo object  from filename and url 
            return new FileInfo(filename, url);
            
        }).collect(Collectors.toList());
        
        return ResponseEntity.status(HttpStatus.OK).body(fileInfos);
    }

    // get file by filename
    @GetMapping("/files/{filename:.+}")
    public ResponseEntity getFile(@PathVariable String filename) {
        Resource file = fileStoreService.load(filename);
        return ResponseEntity.ok()
                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getFilename() + "\"").body(file);
    }

}

package com.webtutsplus.ecommerce.service;

import com.webtutsplus.ecommerce.constants.Constants;
import com.webtutsplus.ecommerce.exceptions.StorageException;
import org.apache.commons.io.FilenameUtils;
import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.stereotype.Service;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.support.ServletUriComponentsBuilder;

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;
import java.util.UUID;
import java.util.stream.Stream;

@Service
public class FIleStoreService {

    Path rootLocation = Paths.get(Constants.UPLOAD_FILE_DIR);

    public String store(MultipartFile file) {
        try {
            if (file.isEmpty()) {
                throw new StorageException("Failed to store empty file.");
            }
            // find extension of the file,png or jpg
            String extension = FilenameUtils.getExtension(file.getOriginalFilename());

            // generate a random unique name for the image
            String uploadedFileName = UUID.randomUUID().toString() + "." + extension;

            // create a path for destination file
            Path destinationFile = rootLocation.resolve(Paths.get(uploadedFileName))
                                   .normalize().toAbsolutePath();

            // Copy input file to destination file path
            try (InputStream inputStream = file.getInputStream()) {
                Files.copy(inputStream, destinationFile,
                        StandardCopyOption.REPLACE_EXISTING);

                final String baseUrl =
                        ServletUriComponentsBuilder.fromCurrentContextPath().build().toUriString();

                //create the public Image URl where we can find the image
                final StringBuilder imageStringBuilder = new StringBuilder(baseUrl);
                imageStringBuilder.append("/fileUpload/files/");
                imageStringBuilder.append(uploadedFileName);

                return imageStringBuilder.toString();
            }
        }
        catch (IOException e) {
            throw new StorageException("Failed to store file.", e);
        }
    }

    public Stream loadAll() {
        // load all the files
        try {
            return Files.walk(this.rootLocation, 1)
                    // ignore the root path
                    .filter(path -> !path.equals(this.rootLocation))
                    .map(this.rootLocation::relativize);
        }
        catch (IOException e) {
            throw new StorageException("Failed to read stored files", e);
        }

    }

    public Resource load(String filename) {
        try {
            // read the file based on the filename
            Path file = rootLocation.resolve(filename);
            // get resource from path
            Resource resource = new UrlResource(file.toUri());

            if (resource.exists() || resource.isReadable()) {
                return resource;
            } else {
                throw new RuntimeException("Could not read the file!");
            }
        } catch (MalformedURLException e) {
            throw new RuntimeException("Error: " + e.getMessage());
        }
    }
}