Help Center/ Object Storage Service/ SDK Reference/ Java/ Object Upload (SDK for Java)/ Using CRC64 to Verify File Consistency (SDK for Java)/ Using CRC64 to Verify File Consistency During Downloads
Updated on 2025-12-11 GMT+08:00
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Using CRC64 to Verify File Consistency During Downloads

You can call the following API to obtain the CRC64 value of an object and compare it with the locally calculated CRC64 value to verify data consistency:

Sample Code: Downloading an Object - Resumable

The following code shows how to use CRC64 to verify data consistency during a resumable download:

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import com.obs.services.ObsClient;
import com.obs.services.exception.ObsException;
import com.obs.services.model.DownloadFileRequest;
import com.obs.services.model.DownloadFileResult;
public class DownloadFile001 {
    public static void main(String[] args) {
        // Obtain an AK/SK pair using environment variables or import the AK/SK pair in other ways. Using hard coding may result in leakage.
        // Obtain an AK/SK pair on the management console.
        String ak = System.getenv("ACCESS_KEY_ID");
        String sk = System.getenv("SECRET_ACCESS_KEY_ID");
        // (Optional) If you are using a temporary AK/SK pair and a security token to access OBS, you are advised not to use hard coding, which may result in information leakage.
        // Obtain an AK/SK pair and a security token using environment variables or import them in other ways.
        // String securityToken = System.getenv("SECURITY_TOKEN");
        // Enter the endpoint corresponding to the bucket. CN-Hong Kong is used here as an example. Replace it with the one currently in use.
        String endPoint = "https://obs.ap-southeast-1.myhuaweicloud.com";
        // Obtain an endpoint using environment variables or import it in other ways.
        //String endPoint = System.getenv("ENDPOINT");
        
        // Create an ObsClient instance.
        // Use the permanent AK/SK pair to initialize the client.
        ObsClient obsClient = new ObsClient(ak, sk,endPoint);
        // Use the temporary AK/SK pair and security token to initialize the client.
        // ObsClient obsClient = new ObsClient(ak, sk, securityToken, endPoint);

        try {
            DownloadFileRequest request = new DownloadFileRequest("examplebucket", "objectname");
            // Set the local path the object will be downloaded to.
            request.setDownloadFile("localfile");
            // Set the maximum number of parts that can be concurrently downloaded.
            request.setTaskNum(5);
            // Set the part size to 10 MB.
            request.setPartSize(10 * 1024 * 1024);
            // Enable the resumable download.
            request.setEnableCheckpoint(true);
            // Enable CRC64 verification for the file.
            request.setNeedCalculateCRC64(true);
            // Perform a resumable download.
            DownloadFileResult result = obsClient.downloadFile(request);
            System.out.println("Server returned crc64 string:" + result.getObjectMetadata().getCrc64());
            System.out.println("downloadFile successfully");
        } catch (ObsException e) {
            System.out.println("downloadFile failed");
            // Request failed. Print the HTTP status code.
            System.out.println("HTTP Code:" + e.getResponseCode());
            // Request failed. Print the server-side error code.
            System.out.println("Error Code:" + e.getErrorCode());
            // Request failed. Print the error details.
            System.out.println("Error Message:" + e.getErrorMessage());
            // Request failed. Print the request ID.
            System.out.println("Request ID:" + e.getErrorRequestId());
            System.out.println("Host ID:" + e.getErrorHostId());
            e.printStackTrace();
        } catch (Exception e) {
            System.out.println("downloadFile failed");
            // Print other error information.
            e.printStackTrace();
        }
    }
}