File upload and download handling

package com.example.demo.service;

import com.example.demo.dto.FileMetadata;
import com.example.demo.exception.FileStorageException;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;
import org.springframework.web.multipart.MultipartFile;

import java.io.IOException;
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;

@Service
public class FileStorageService {

    private final Path fileStorageLocation;

    public FileStorageService(@Value("${file.upload-dir:uploads}") String uploadDir) {
        this.fileStorageLocation = Paths.get(uploadDir).toAbsolutePath().normalize();
        try {
            Files.createDirectories(this.fileStorageLocation);
        } catch (Exception ex) {
            throw new FileStorageException("Could not create upload directory", ex);
        }
    }

    public FileMetadata storeFile(MultipartFile file) {
        String originalFileName = StringUtils.cleanPath(file.getOriginalFilename());

        // Validate file
        if (originalFileName.contains("..")) {
            throw new FileStorageException("Invalid file path: " + originalFileName);
        }

        if (file.isEmpty()) {
            throw new FileStorageException("Cannot store empty file");
        }

        // Generate unique filename
        String extension = originalFileName.substring(originalFileName.lastIndexOf("."));
        String storedFileName = UUID.randomUUID().toString() + extension;

        try {
            Path targetLocation = this.fileStorageLocation.resolve(storedFileName);
            Files.copy(file.getInputStream(), targetLocation,
                StandardCopyOption.REPLACE_EXISTING);

            FileMetadata metadata = new FileMetadata();
            metadata.setFileName(storedFileName);
            metadata.setOriginalFileName(originalFileName);
            metadata.setContentType(file.getContentType());
            metadata.setSize(file.getSize());

            return metadata;
        } catch (IOException ex) {
            throw new FileStorageException("Failed to store file " + originalFileName, ex);
        }
    }

    public Resource loadFileAsResource(String fileName) {
        try {
            Path filePath = this.fileStorageLocation.resolve(fileName).normalize();
            Resource resource = new UrlResource(filePath.toUri());

            if (resource.exists()) {
                return resource;
            } else {
                throw new FileStorageException("File not found: " + fileName);
            }
        } catch (MalformedURLException ex) {
            throw new FileStorageException("File not found: " + fileName, ex);
        }
    }

    public void deleteFile(String fileName) {
        try {
            Path filePath = this.fileStorageLocation.resolve(fileName).normalize();
            Files.deleteIfExists(filePath);
        } catch (IOException ex) {
            throw new FileStorageException("Failed to delete file: " + fileName, ex);
        }
    }
}