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  5. Performing a Resumable Upload

Performing a Resumable Upload

Uploading large files often fails due to poor network conditions or program breakdowns. It is a waste of resources to restart the upload process upon an upload failure, and the restarted upload process may still suffer from the unstable network. To resolve such issues, you can use the API for resumable upload, whose working principle is to divide the to-be-uploaded file into multiple parts and upload them separately. The upload result of each part is recorded in a checkpoint file in real time. Only when all parts are successfully uploaded, the result indicating a successful upload will be returned. Otherwise, an exception is thrown to remind you of calling the API again for re-uploading. Based on the upload status of each part recorded in the checkpoint file, the re-uploading will upload the parts failed to be uploaded previously, instead of uploading all parts. By virtue of this, resources are saved and efficiency is improved.

You can call ObsClient.uploadFile to perform a resumable upload. The following table describes the parameters involved in this API.



Method in OBS Java SDK


(Mandatory) Bucket name



(Mandatory) Object name



(Mandatory) Local file to be uploaded



Part size, in bytes. The value ranges from 100 KB to 5 GB and defaults to 5 MB.



Maximum number of parts that can be concurrently uploaded. The default value is 1.



Whether to enable the resumable upload mode. The default value is false, which indicates that this mode is disabled.



File used to record the upload progress. This parameter is effective only in the resumable upload mode. If this parameter is null, the file will be in the same directory as the local file to be uploaded.



Object properties



Whether to verify the content of the to-be-uploaded file. This parameter is effective only in the resumable upload mode. The default value is false, which indicates that the content will not be verified.


Sample code:

String endPoint = "yourdomainname";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";

// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);
UploadFileRequest request = new UploadFileRequest("bucketname", "objectkey");
// Specify the local file to be uploaded.
// Set the maximum number of parts that can be concurrently uploaded.
// Set the part size to 10 MB.
request.setPartSize(10 * 1024 * 1024);
// Enable resumable upload.
 // Perform a resumable upload.
    CompleteMultipartUploadResult result = obsClient.uploadFile(request);
}catch (ObsException e) {
// When an exception occurs, you can call the API for resumable upload again to perform re-uploading.
// Close obsClient.
  • The API for resumable upload, which is implemented based on multipart upload, is an encapsulated and enhanced version of multipart upload.
  • This API saves resources and improves efficiency upon the re-upload, and speeds up the upload process by concurrently uploading parts. Because this API is transparent to users, users are free from concerns about internal service details, such as the creation and deletion of checkpoint files, division of objects, and concurrent upload of parts.
  • The default value of the enableCheckpoint parameter is false, which indicates that the resumable upload mode is disabled. In such cases, this API degrades to the simple encapsulation of multipart upload, and no checkpoint file will be generated.
  • checkpointFile and enableCheckSum are effective only when enableCheckpoint is true.