If you want to download a large object or it takes a long time to download an object at a time, you can use streaming download to download the object incrementally until the entire object is downloaded.

Usage notes

  • In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS by using other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about the regions and endpoints supported by OSS, see Regions and endpoints.
  • In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient by using custom domain names or STS, see Create an OSSClient instance.
  • The oss:GetObject permission is required to use streaming download. For more information, see Attach a custom policy to a RAM user.

Examples

The following code provides an example on how to use streaming download to download an object named exampleobject.txt from a bucket named examplebucket:

import com.aliyun.oss.OSS;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.model.*;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Demo {
    public static void main(String[] args) {
        // In this example, the endpoint of the China (Hangzhou) region is used. Specify the actual endpoint. For more information about the endpoints of other regions, see Regions and endpoints. 
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // Security risks may arise if you use the AccessKey pair of an Alibaba Cloud account to access Object Storage Service (OSS) because the account has permissions on all API operations. We recommend that you use a RAM user to call API operations or perform routine O&M. To create a RAM user, log on to the RAM console. 
        String accessKeyId = "yourAccessKeyId";
        String accessKeySecret = "yourAccessKeySecret";
        // Specify the name of the bucket. Example: examplebucket. 
        String bucketName = "examplebucket";
        // Specify the full path of the object. Example: exampledir/exampleobject.txt. The full path of the object cannot contain the bucket name. 
        String objectName = "exampledir/exampleobject.txt";

        // Create an OSSClient instance. 
        OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);
        try {
            // ossObject specifies the bucket name, object name, object metadata, and an input stream. 
            OSSObject ossObject = ossClient.getObject(bucketName, objectName);              

            // Read the object content. 
            System.out.println("Object content:");
            BufferedReader reader = new BufferedReader(new InputStreamReader(ossObject.getObjectContent()));
            while (true) {
                String line = reader.readLine();
                if (line == null) break;

                System.out.println("\n" + line);
            }
            // You must close the stream after the data is read. Otherwise, connection leaks may occur. Consequently, no connections are available and an exception occurs. 
            reader.close();
            // If you do not close the ossObject object after it is used, connection leaks may occur. Consequently, no connections are available and an exception occurs.             
            ossObject.close();
       
        } catch (OSSException oe) {
            System.out.println("Caught an OSSException, which means your request made it to OSS, "
                    + "but was rejected with an error response for some reason.");
            System.out.println("Error Message:" + oe.getErrorMessage());
            System.out.println("Error Code:" + oe.getErrorCode());
            System.out.println("Request ID:" + oe.getRequestId());
            System.out.println("Host ID:" + oe.getHostId());
        } catch (Throwable ce) {
            System.out.println("Caught an ClientException, which means the client encountered "
                    + "a serious internal problem while trying to communicate with OSS, "
                    + "such as not being able to access the network.");
            System.out.println("Error Message:" + ce.getMessage());
        } finally {
            if (ossClient != null) {
                ossClient.shutdown();
            }
        }
    }
}            

References

  • For more information about the complete sample code for streaming download, visit GitHub.
  • For more information about the API operation that is called to perform streaming download, see GetObject.