动态图片在Web应用中实时加载与显示的最佳实践

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

public class ImageDownloader {

    private static final String BASE_IMAGE_DIR = "/path/to/your/server/images/"; // 替换为实际的服务器图片存储路径

    /**
     * 下载图片并保存到服务器指定目录
     * @param imageUrl 待下载图片的URL
     * @param fileName 图片保存的文件名 (例如: img.png)
     * @return 保存后的图片在服务器上的完整路径，如果失败则返回null
     */
    public static Path downloadAndSaveImage(String imageUrl, String fileName) {
        Path targetPath = Paths.get(BASE_IMAGE_DIR, fileName);
        try {
            URL url = new URL(imageUrl);
            try (InputStream in = url.openStream()) {
                Files.copy(in, targetPath, StandardCopyOption.REPLACE_EXISTING);
                System.out.println("图片下载成功并保存到: " + targetPath);
                return targetPath;
            }
        } catch (IOException e) {
            System.err.println("下载图片失败: " + e.getMessage());
            return null;
        }
    }

    // 示例用法
    public static void main(String[] args) {
        // 假设有一个图片链接
        String remoteImageUrl = "https://example.com/some-remote-image.jpg";
        String localFileName = "downloaded_image.jpg";

        Path savedPath = downloadAndSaveImage(remoteImageUrl, localFileName);
        if (savedPath != null) {
            System.out.println("图片已准备好被Web服务提供: " + savedPath.getFileName());
        }
    }
}

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 {

    // 替换为实际的服务器图片存储路径
    private static final String SERVER_IMAGE_DIRECTORY = "file:/path/to/your/server/images/"; 
    // 替换为Web应用中访问图片的URL前缀
    private static final String WEB_ACCESS_PATH = "/dynamic-images/**"; 

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler(WEB_ACCESS_PATH)
                .addResourceLocations(SERVER_IMAGE_DIRECTORY);
    }
}

import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import java.net.MalformedURLException;
import java.nio.file.Path;
import java.nio.file.Paths;

@RestController
public class ImageController {

    private static final String BASE_IMAGE_DIR = "/path/to/your/server/images/"; // 替换为实际的服务器图片存储路径

    @GetMapping("/images/{filename:.+}") // {filename:.+} 允许文件名包含点
    public ResponseEntity<Resource> serveImage(@PathVariable String filename) {
        try {
            Path filePath = Paths.get(BASE_IMAGE_DIR).resolve(filename).normalize();
            Resource resource = new UrlResource(filePath.toUri());

            if (resource.exists() && resource.isReadable()) {
                // 根据文件扩展名设置Content-Type
                String contentType = "application/octet-stream";
                if (filename.endsWith(".png")) {
                    contentType = MediaType.IMAGE_PNG_VALUE;
                } else if (filename.endsWith(".jpg") || filename.endsWith(".jpeg")) {
                    contentType = MediaType.IMAGE_JPEG_VALUE;
                } // 可以添加更多图片类型

                return ResponseEntity.ok()
                        .contentType(MediaType.parseMediaType(contentType))
                        .body(resource);
            } else {
                return ResponseEntity.notFound().build();
            }
        } catch (MalformedURLException e) {
            return ResponseEntity.badRequest().build();
        }
    }
}

import com.vaadin.flow.component.html.Image;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.router.Route;

@Route("dynamic-image-display")
public class DynamicImageDisplayView extends VerticalLayout {

    public DynamicImageDisplayView() {
        // 假设图片名为 "downloaded_image.jpg"
        // 并且通过 /dynamic-images/ 或 /images/ 前缀暴露
        String imageUrl = "/dynamic-images/downloaded_image.jpg"; // 如果使用静态资源处理器
        // 或者 String imageUrl = "/images/downloaded_image.jpg"; // 如果使用自定义端点

        Image dynamicImage = new Image(imageUrl, "动态加载的图片");
        dynamicImage.setHeight("200px");
        dynamicImage.setWidth("auto");

        add(dynamicImage);
    }
}