This topic describes how to manage symbolic links in a versioned bucket.

Create a symbolic link

You can create a symbolic link to which the current version of an object points.
Note In a versioned bucket, a symbolic link cannot be created for a delete marker.

A symbolic link can have multiple versions. You can call the PutSymlink operation to point each version of a symbolic link to different objects. In this case, the IDs of the versions are generated by OSS and are returned in the response as the x-oss-version-id header.

The following code provides an example on how to create a symbolic link:

import com.aliyun.oss.ClientException;
import com.aliyun.oss.OSS;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.model.*;

public class Demo {
    public static void main(String[] args) throws Exception {
        // In this example, the endpoint of the China (Hangzhou) region is used. Specify the actual endpoint. 
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // The AccessKey pair of an Alibaba Cloud account has permissions on all API operations. Using these credentials to access OSS is a high-risk operation. 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 name of the symbolic link that you want to create. 
        String symLink = "yourSymLink";
        // Specify the full path of the object. The full path of the object cannot contain the bucket name. 
        String destinationObjectName = "exampledir/object";

        // Create an OSSClient instance. 
        OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);

        try {
            // Create metadata for the object that you want to upload. 
            ObjectMetadata metadata = new ObjectMetadata();
            metadata.setContentType("text/plain");
            // Set the value of the property parameter for the user metadata to property-value. 
            metadata.addUserMetadata("property", "property-value");

            // Create a request (CreateSymlinkRequest) to create the symbolic link. 
            CreateSymlinkRequest createSymlinkRequest = new CreateSymlinkRequest(bucketName, symLink, destinationObjectName);

            // Configure the metadata. 
            createSymlinkRequest.setMetadata(metadata);

            // Create the symbolic link. 
            ossClient.createSymlink(createSymlinkRequest);
        } 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();
            }
        }
    }
}

Query a symbolic link

By default, the GetSymlink operation is called to query the current version of a symbolic link. You can specify the version ID in the request to query the specified version of a symbolic link. If the current version of the symbolic link is a delete marker, OSS returns 404 Not Found and includes x-oss-delete-marker = true and x-oss-version-id in the response header.
Note To query a symbolic link, you must have read permissions on the symbolic link.

The following code provides an example on how to query a symbolic link:

import com.aliyun.oss.ClientException;
import com.aliyun.oss.OSS;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.model.*;

public class Demo {
    public static void main(String[] args) throws Exception {
        // In this example, the endpoint of the China (Hangzhou) region is used. Specify the actual endpoint. 
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // The AccessKey pair of an Alibaba Cloud account has permissions on all API operations. Using these credentials to access OSS is a high-risk operation. 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 name of the symbolic link that you want to query. 
        String symLink = "yourSymLink";
        // Specify the version ID of the symbolic link that you want to query. 
        String versionId  = "CAEQMxiBgICAof2D0BYiIDJhMGE3N2M1YTI1NDQzOGY5NTkyNTI3MGYyMzJm****";

        // Create an OSSClient instance. 
        OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);

        try {
            // Query the content of the symbolic link with the specified version ID. 
            GenericRequest genericRequest = new GenericRequest(bucketName, symLink, versionId);
            OSSSymlink symbolicLink = ossClient.getSymlink(genericRequest);
            // Display the content of the object to which the symbolic link points. 
            System.out.println(symbolicLink.getSymlink());
            System.out.println(symbolicLink.getTarget());
            System.out.println(symbolicLink.getRequestId());            
            System.out.println(symbolicLink.getMetadata().getVersionId());
        } 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 create a symbolic link, see PutSymlink.
  • For more information about the API operation that you can call to query a symbolic link, see GetSymlink.