Perform streaming download by using OSS SDK for Java-Object Storage Service(OSS)-阿里云帮助中心

When working with large objects or processing data incrementally, you can use streaming download to read object content from OSS in chunks to avoid loading the entire object into memory at once, thereby improving the efficiency and performance. This method is suitable for downloading objects that exceed memory limits, processing data in real-time to reduce memory usage, and scenarios where data is retrieved step by step over the network.

Usage notes

In this topic, the public endpoint of the China (Hangzhou) region is used. To access OSS from other Alibaba Cloud services in the same region, use an internal endpoint. For details about supported regions and endpoints, see Regions and endpoints.
In this topic, access credentials are obtained from environment variables. For more information, see Configure access credentials.
This topic demonstrates creating an OSSClient instance with an OSS endpoint. For alternative configurations, such as using a custom domain or authenticating with credentials from Security Token Service (STS), see Client configuration.
To use streaming download, you must have the oss:GetObject permission. For more information, see Grant a custom policy.

Sample code

The following code provides an example on how to read object content from OSS in chunks and store it in a byte array.

import com.aliyun.oss.ClientBuilderConfiguration;
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.common.comm.SignVersion;
import com.aliyun.oss.model.*;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;

public class Stream {
    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";
        // Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to cn-hangzhou.
        String region = "cn-hangzhou";

        // Create an OSSClient instance.
        // Call the shutdown method to release resources when the OSSClient is no longer in use. 
        ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
        clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
        OSS ossClient = OSSClientBuilder.create()
                .endpoint(endpoint)
                .credentialsProvider(credentialsProvider)
                .clientConfiguration(clientBuilderConfiguration)
                .region(region)
                .build();

        try {
            // ossObject includes the bucket name, object name, object metadata, and an input stream. 
            OSSObject ossObject = ossClient.getObject(bucketName, objectName);
            InputStream inputStream = ossObject.getObjectContent();
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            // Read the object content and store it in a byte array. 
            byte[] readBuffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(readBuffer)) != -1) {
                byteArrayOutputStream.write(readBuffer, 0, bytesRead);
            }
            // Obtain the final result.
            byte[] fileBytes = byteArrayOutputStream.toByteArray();
            // Display the length of the byte array.
            System.out.println("Downloaded file size: " + fileBytes.length + " bytes");
            // 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. 
            inputStream.close();
            byteArrayOutputStream.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();
            }
        }
    }
}

Below is the sample code for downloading the data of an object named exampleobject.txt from a stream as a file named examplefile.txt in the D:\localpath directory:

import com.aliyun.oss.ClientBuilderConfiguration;
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.common.comm.SignVersion;
import com.aliyun.oss.model.OSSObject;

import java.io.*;

public class GetObjectStreamtoLocalFile {
    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";
        // Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to cn-hangzhou.
        String region = "cn-hangzhou";

        // Specify the local path in which you want to store the files.
        String localFilePath = "D:\\localpath\\examplefile.txt"; // Specify the path of the local file.

        // Create an OSSClient instance. 
        // Call the shutdown method to release resources when the OSSClient is no longer in use.
        ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
        clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
        OSS ossClient = OSSClientBuilder.create()
                .endpoint(endpoint)
                .credentialsProvider(credentialsProvider)
                .clientConfiguration(clientBuilderConfiguration)
                .region(region)
                .build();

        try {
            // Retrieve the object's input stream.
            OSSObject ossObject = ossClient.getObject(bucketName, objectName);
            InputStream inputStream = ossObject.getObjectContent();

            // Create an output stream to the local file.
            try (FileOutputStream fileOutputStream = new FileOutputStream(localFilePath)) {
                byte[] buffer = new byte[1024];
                int bytesRead;

                // Read the content in chunks and write it to a local file.
                while ((bytesRead = inputStream.read(buffer)) != -1) {
                    fileOutputStream.write(buffer, 0, bytesRead);
                }

                System.out.println("Downloaded file saved to: " + localFilePath);
            }

            // Close the input stream.
            inputStream.close();
            // Close ossObject.
            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.