oss 下载文件 并把文件返回前端

可以使用阿里云提供的 Object Storage Service (OSS) SDK，在后端通过 API 下载文件并返回给前端。以下是简单的示例代码：

import com.aliyun.oss.OSS;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.model.GetObjectRequest;
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.Service;

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.net.URLEncoder;

@Service
public class OssService {

    @Value("${oss.endpoint}")
    private String endpoint;

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

    @Value("${oss.accessKeySecret}")
    private String accessKeySecret;

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

    public ResponseEntity<Resource> downloadFile(String objectName) {
        OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);

        GetObjectRequest getObjectRequest = new GetObjectRequest(bucketName, objectName);
        InputStream inputStream = ossClient.getObject(getObjectRequest).getObjectContent();
        InputStreamResource resource = new InputStreamResource(inputStream);

        HttpHeaders headers = new HttpHeaders();
        headers.add(HttpHeaders.CONTENT_DISPOSITION,
                "inline;filename*=UTF-8''" + URLEncoder.encode(objectName, "UTF-8"));
        headers.add(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_OCTET_STREAM_VALUE);
        headers.setContentLength(Long.parseLong(getObjectRequest.getResponseHeaders().get("Content-Length").get(0)));

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

}

在这个例子中，我们通过`OSS`对象的`getObject`方法下载文件，将文件转换为`InputStream`，将其作为响应体返回给前端。要将文件名作为响应头，在这里使用了`Content-Disposition`和`filename*`参数。注意，需要使用`URLencoder`进行URL编码，以避免中文乱码问题。