Java Web应用中运行时动态图片资源的正确处理策略

import java.io.File;
import java.nio.file.Path;
import java.nio.file.Paths;

public class FileStorageConfig {
    public static String getUploadBaseDir() {
        // 推荐使用用户主目录下的子目录，确保权限和持久性
        String uploadDir = System.getProperty("user.home") + File.separator + "my-app-uploads";
        File dir = new File(uploadDir);
        if (!dir.exists()) {
            dir.mkdirs(); // 如果目录不存在，则创建
        }
        return uploadDir;
    }
}

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;

public class ImageDownloaderService {

    /**
     * 从指定URL下载图片并保存到服务器的指定目录。
     * @param imageUrl 图片的URL
     * @param fileName 保存的文件名（例如："image123.png"）
     * @return 保存后的文件绝对路径
     * @throws IOException 如果下载或保存过程中发生错误
     */
    public static String downloadAndSaveImage(String imageUrl, String fileName) throws IOException {
        String uploadBaseDir = FileStorageConfig.getUploadBaseDir(); // 获取基础上传目录
        Path targetPath = Paths.get(uploadBaseDir, fileName);

        try (InputStream in = new URL(imageUrl).openStream()) {
            Files.copy(in, targetPath, StandardCopyOption.REPLACE_EXISTING);
        }
        return targetPath.toString(); // 返回文件在服务器上的绝对路径
    }
}

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        String uploadDir = FileStorageConfig.getUploadBaseDir(); // 获取上传目录
        // 将URL路径 "/uploaded-images/**" 映射到文件系统路径 "file:/path/to/my-app-uploads/"
        registry.addResourceHandler("/uploaded-images/**")
                .addResourceLocations("file:" + uploadDir + File.separator); // 注意末尾的File.separator
    }
}

// 假设图片文件名为 "downloaded_image_123.png"
Image imageComponent = new Image("/uploaded-images/downloaded_image_123.png", "Downloaded Image");
add(imageComponent);

import org.springframework.core.io.FileSystemResource;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.io.IOException;

@Controller
public class ImageServingController {

    private final String uploadBaseDir = FileStorageConfig.getUploadBaseDir();

    @GetMapping("/image/{imageName}")
    public ResponseEntity<FileSystemResource> getImage(@PathVariable String imageName) throws IOException {
        // 简单路径验证，防止路径遍历攻击
        if (imageName.contains("..") || imageName.contains("/") || imageName.contains("\")) {
            return ResponseEntity.badRequest().build();
        }

        File imageFile = Paths.get(uploadBaseDir, imageName).toFile();

        if (!imageFile.exists() || !imageFile.isFile()) {
            return ResponseEntity.notFound().build();
        }

        // 猜测文件类型，或根据业务逻辑确定
        String contentType = Files.probeContentType(imageFile.toPath());
        if (contentType == null) {
            contentType = MediaType.APPLICATION_OCTET_STREAM_VALUE; // 默认二进制流
        }

        return ResponseEntity.ok()
                .contentType(MediaType.parseMediaType(contentType))
                .body(new FileSystemResource(imageFile));
    }
}

// 假设图片文件名为 "downloaded_image_123.png"
Image imageComponent = new Image("/image/downloaded_image_123.png", "Downloaded Image");
add(imageComponent);