Object Storage Service:Conditional download (OSS SDK for Java 1.0)

Download conditions

OSS supports the following download conditions.

Usage notes

• This topic uses the public endpoint of the China (Hangzhou) region. To access OSS from other Alibaba Cloud services in the same region, 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, 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.

• Conditional download requires the oss:GetObject permission. For more information, see Grant a custom policy.

Examples

The following code downloads an object with conditions by using ossClient.getObject. You can also use ossClient.downloadFile in a similar way.

import com.aliyun.oss.*;
import com.aliyun.oss.common.auth.*;
import com.aliyun.oss.common.comm.SignVersion;
import com.aliyun.oss.model.GetObjectRequest;
import java.io.File;
import java.util.Date;

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. 
        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. Do not include the bucket name in the full path. Example: testfolder/exampleobject.txt. 
        String objectName = "testfolder/exampleobject.txt";
        String pathName = "D:\\localpath\\examplefile.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 associated 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 {
            GetObjectRequest request = new GetObjectRequest(bucketName, objectName);
            // For example, an object was last modified at 13:27:04, September 26, 2023. If the specified time is earlier than the last modified time, such as Tue Sep 25 13:27:04 CST 2023, the object meets the If-Modified-Since condition and the object is downloaded. 
            request.setModifiedSinceConstraint(new Date("Tue Sep 25 13:27:04 CST 2023"));

            // Download the object to your local device. 
            ossClient.getObject(request, new File(pathName));
        } 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 (ClientException 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 API operation that you can call to perform conditional download, see GetObject.