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Object Storage Service:Streaming download

Last Updated:Oct 20, 2023

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, access credentials are obtained from environment variables. For more information about how to configure access credentials, see Configure access credentials.

  • In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Create an OSSClient instance.

  • To use streaming download, you must have the oss:GetObject permission. For more information, see Attach a custom policy to a RAM user.

Sample code

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

import com.aliyun.oss.OSS;
import com.aliyun.oss.common.auth.*;
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) throws Exception {
        // In this example, the endpoint of the China (Hangzhou) region is used. Specify your actual endpoint. For more information about the endpoints of other regions, see Regions and endpoints. 
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. 
        EnvironmentVariableCredentialsProvider credentialsProvider = CredentialsProviderFactory.newEnvironmentVariableCredentialsProvider();
        // Specify the name of the bucket. Example: examplebucket. 
        String bucketName = "examplebucket";
        // Specify the full path of the object. Example: exampledir/exampleobject.txt. Do not include the bucket name in the full path. 
        String objectName = "exampledir/exampleobject.txt";

         // Create an OSSClient instance. 
        OSS ossClient = new OSSClientBuilder().build(endpoint, credentialsProvider);
        try {
            // ossObject includes 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 obtained stream after the object 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 the complete sample code that is used to perform streaming download, visit GitHub.

  • For more information about the API operation that you can call to perform streaming download, see GetObject.