springboot ServletOutputStream 结合S3TransferManager DownloadFileRequestj进行文件下载

在Spring Boot应用程序中，您可以使用`@RequestMapping`注解来创建一个处理文件下载请求的Controller。您可以在Controller中使用`S3TransferManager`下载文件并将其写入`ServletOutputStream`。下面是一个示例代码片段，演示如何将从Amazon S3下载的文件写入`ServletOutputStream`：

import com.amazonaws.services.s3.transfer.Download;
import com.amazonaws.services.s3.transfer.TransferManager;
import com.amazonaws.services.s3.transfer.TransferManagerBuilder;
import com.amazonaws.services.s3.transfer.model.DownloadResult;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.InputStreamResource;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpHeaders;
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 javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLEncoder;

@Controller
public class FileDownloadController {

    @Value("${aws.s3.bucketName}")
    private String bucketName;

    @Value("${aws.s3.region}")
    private String region;

    @Value("${aws.s3.accessKeyId}")
    private String accessKeyId;

    @Value("${aws.s3.secretAccessKey}")
    private String secretAccessKey;

    @GetMapping("/download/{key}")
    public ResponseEntity<Resource> downloadFile(@PathVariable String key, HttpServletResponse response) throws IOException {
        TransferManager transferManager = TransferManagerBuilder.standard()
                .withS3Client(AmazonS3ClientBuilder.standard()
                        .withRegion(region)
                        .withCredentials(new AWSStaticCredentialsProvider(new BasicAWSCredentials(accessKeyId, secretAccessKey)))
                        .build())
                .build();

        File file = new File(key);
        Download download = transferManager.download(bucketName, key, file);

        InputStream inputStream = new FileInputStream(file);
        InputStreamResource resource = new InputStreamResource(inputStream);

        HttpHeaders headers = new HttpHeaders();
        headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + URLEncoder.encode(key, "UTF-8") + "\"");
        headers.add(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_OCTET_STREAM_VALUE);
        headers.add(HttpHeaders.CONTENT_LENGTH, file.length() + "");
        headers.add(HttpHeaders.CACHE_CONTROL, "no-cache, no-store, must-revalidate");
        headers.add(HttpHeaders.PRAGMA, "no-cache");
        headers.add(HttpHeaders.EXPIRES, "0");

        return ResponseEntity.ok()
                .headers(headers)
                .body(resource);
    }
}

在上面的代码中，`@GetMapping("/download/{key}")`用于创建一个处理文件下载请求的Controller方法。`TransferManager`用于下载文件，其中`bucketName`是存储桶名称，`region`是存储桶所在的区域，`accessKeyId`和`secretAccessKey`是AWS的访问密钥。

在下载完成后，将文件内容写入`HttpServletResponse`中，通过设置`Content-Disposition`响应头，指定浏览器以附件形式下载文件。最后，将文件内容写入`InputStreamResource`并返回`ResponseEntity`对象。