Initializing a Multipart Upload

Before upload, you need to notify OBS of initializing a multipart upload. This operation will return an upload ID (globally unique identifier) created by the OBS server to identify the multipart upload. You can use this upload ID to initiate related operations, such as aborting a multipart upload, listing multipart uploads, and listing uploaded parts.

You can call ObsClient.initiateMultipartUpload to initialize a multipart upload.

The following table describes the parameters involved in this API.

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

InitiateMultipartUploadRequest request = new InitiateMultipartUploadRequest("bucketname", "objectname");
ObjectMetadata metadata = new ObjectMetadata();
metadata.addUserMetadata("property", "property-value");
metadata.setContentType("text/plain");
request.setMetadata(metadata);
InitiateMultipartUploadResult result = obsClient.initiateMultipartUpload(request);

String uploadId = result.getUploadId();
System.out.println("\t" + uploadId);

• Call InitiateMultipartUploadRequest to specify the name and owning bucket of the uploaded object.
• In InitiateMultipartUploadRequest, you can specify the MIME type, storage class, and customized metadata for the object.
• The upload ID of the multipart upload returned by InitiateMultipartUploadResult.getUploadId will be used in follow-up operations.

Uploading a Part

After initializing a multipart upload, you can specify the object name and upload ID to upload a part. Each upload part has a part number (ranging from 1 to 10000). For parts with the same upload ID, their part numbers are unique and identify their comparative locations in the object. If you use the same part number to upload two parts, the later one being uploaded will overwrite the former. Except for the part last uploaded whose size ranges from 0 to 5 GB, sizes of the other parts range from 100 KB to 5 GB. Parts are uploaded in random order and can be uploaded through different processes or machines. OBS will combine them into the object based on their part numbers.

You can call ObsClient.uploadPart to upload a part.

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
String uploadId = "upload id from initiateMultipartUpload";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

List<PartEtag> partEtags = new ArrayList<PartEtag>();
// Upload the first part.
UploadPartRequest request = new UploadPartRequest("bucketname", "objectname");
// Set an upload ID.
request.setUploadId(uploadId);
// Set a part number, which ranges from 1 to 10000.
request.setPartNumber(1);
// Set the large file to be uploaded.
request.setFile(new File("localfile"));

// Set the part size.
request.setPartSize(5 * 1024 * 1024L);
UploadPartResult result = obsClient.uploadPart(request);
partEtags.add(new PartEtag(result.getEtag(), result.getPartNumber()));

// Upload the second part.
request = new UploadPartRequest("bucketname", "objectname");
// Set an upload ID.
request.setUploadId(uploadId);
// Set the part number.
request.setPartNumber(2);
// Set the large file to be uploaded.
request.setFile(new File("localfile"));
// Set the offset of the second part.
request.setOffset(5 * 1024 * 1024L);
// Set the part size.
request.setPartSize(5 * 1024 * 1024L);
result = obsClient.uploadPart(request);
partEtags.add(new PartEtag(result.getEtag(), result.getPartNumber()));

• Except the part last uploaded, other parts must be larger than 100 KB. Part sizes will not be verified during upload because which one is last uploaded is not identified until parts are combined.
• OBS will return ETags (MD5 values) of the received parts to users.
• To ensure data integrity, set UploadPartRequest.setAttachMd5 to true to make the SDK automatically calculate the MD5 value (valid only when the data source is a local file) of each part and add the MD5 value to the Content-MD5 request header. The OBS server will compare the MD5 value contained by each part and that calculated by the SDK to verify the data integrity.
• You can call UploadPartRequest.setContentMd5 to set the MD5 value of the uploaded data directly. If this value is set, the UploadPartRequest.setAttachMd5 parameter becomes ineffective.
• Part numbers range from 1 to 10000. If the part number you set is out of this range, OBS will return error 400 Bad Request.
• The minimum part size supported by an OBS 3.0 bucket is 100 KB, and the minimum part size supported by an OBS 2.0 bucket is 5 MB.

Combining Parts

After all parts are uploaded, call the API for combining parts to generate the object. Before this operation, valid part numbers and ETags of all parts must be sent to OBS. After receiving this information, OBS verifies the validity of each part one by one. After all parts pass the verification, OBS combines these parts to form the final object.

The following table describes the parameters involved in this API.

You can call ObsClient.completeMultipartUpload to combine parts.

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
String uploadId = "upload id from initiateMultipartUpload";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

List<PartEtag> partEtags = new ArrayList<PartEtag>();
// First part
PartEtag part1 = new PartEtag();
part1.setPartNumber(1);
part1.seteTag("etag1");
partEtags.add(part1);

// Second part
PartEtag part2 = new PartEtag();
part2.setPartNumber(2);
part2.setEtag("etag2");
partEtags.add(part2);

CompleteMultipartUploadRequest request = new CompleteMultipartUploadRequest("bucketname", "objectname", uploadId, partEtags);

obsClient.completeMultipartUpload(request);

• In the preceding code, partEtags indicates the list of part numbers and ETags of uploaded parts.
• Part numbers can be inconsecutive.

Concurrently Uploading Parts

Multipart upload is mainly used for large file upload or when the network condition is poor. The following sample code shows how to concurrently upload parts in a multipart upload:

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
final String bucketName = "bucketname";
final String objectKey = "objectname";
// Create an instance of ObsClient.
final ObsClient obsClient = new ObsClient(ak, sk, endPoint);

// Initialize the thread pool.
ExecutorService executorService = Executors.newFixedThreadPool(20);
final File largeFile = new File("localfile");

// Initialize the multipart upload.
InitiateMultipartUploadRequest request = new InitiateMultipartUploadRequest(bucketName, objectKey);
InitiateMultipartUploadResult result = obsClient.initiateMultipartUpload(request);

final String uploadId = result.getUploadId();
System.out.println("\t"+ uploadId + "\n");

// Set the part size to 100 MB.
long partSize = 100 * 1024 * 1024L;
long fileSize = largeFile.length();

// Calculate the number of parts need to be uploaded.
long partCount = fileSize % partSize == 0 ? fileSize / partSize : fileSize / partSize + 1;

final List<PartEtag> partEtags = Collections.synchronizedList(new ArrayList<PartEtag>());

// Start uploading parts concurrently.
for (int i = 0; i < partCount; i++)
{
    // Start position of parts in the file
    final long offset = i * partSize;
    // Part size
    final long currPartSize = (i + 1 == partCount) ? fileSize - offset : partSize;
    // Part number
    final int partNumber = i + 1;
    executorService.execute(new Runnable()
    {
        @Override
        public void run()
        {
            UploadPartRequest uploadPartRequest = new UploadPartRequest();
            uploadPartRequest.setBucketName(bucketName);
            uploadPartRequest.setObjectKey(objectKey);
            uploadPartRequest.setUploadId(uploadId);
            uploadPartRequest.setFile(largeFile);
            uploadPartRequest.setPartSize(currPartSize);
            uploadPartRequest.setOffset(offset);
            uploadPartRequest.setPartNumber(partNumber);
            
            UploadPartResult uploadPartResult;
            try
            {
                uploadPartResult = obsClient.uploadPart(uploadPartRequest);
                System.out.println("Part#" + partNumber + " done\n");
                partEtags.add(new PartEtag(uploadPartResult.getEtag(), uploadPartResult.getPartNumber()));
            }
            catch (ObsException e)
            {
                e.printStackTrace();
            }
        }
    });
}

// Wait until the upload is complete.
executorService.shutdown();
while (!executorService.isTerminated())
{
    try
    {
        executorService.awaitTermination(5, TimeUnit.SECONDS);
    }
    catch (InterruptedException e)
    {
        e.printStackTrace();
    }
}
// Combine parts.
CompleteMultipartUploadRequest completeMultipartUploadRequest = new CompleteMultipartUploadRequest(bucketName, objectKey, uploadId, partEtags);
obsClient.completeMultipartUpload(completeMultipartUploadRequest);

Aborting a Multipart Upload

After a multipart upload is aborted, you cannot use its upload ID to perform any operation and the uploaded parts will be deleted by OBS.

When an object is being uploaded in multi-part mode or an object fails to be uploaded, parts are generated in the bucket. These parts occupy your storage space. You can cancel the multi-part uploading task to delete unnecessary parts, thereby saving the storage space.

You can call ObsClient.abortMultipartUpload to abort a multipart upload.

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
String uploadId = "upload id from initiateMultipartUpload";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

AbortMultipartUploadRequest request = new AbortMultipartUploadRequest("bucketname", "objectname", uploadId);

obsClient.abortMultipartUpload(request);

Listing Uploaded Parts

You can call ObsClient.listParts to list successfully uploaded parts of a multipart upload.

The following table describes the parameters involved in this API.

• Listing parts in simple mode

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
String uploadId = "upload id from initiateMultipartUpload";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

//List the uploaded parts. uploadId is obtained frominitiateMultipartUpload.        
ListPartsRequest request = new ListPartsRequest("bucketname", "objectname");
request.setUploadId(uploadId);
ListPartsResult result = obsClient.listParts(request);

for(Multipart part : result.getMultipartList()){
    // Part number, specified when uploading
   System.out.println("\t"+part.getPartNumber());
    // Part size
   System.out.println("\t"+part.getSize());
    // Part ETag
   System.out.println("\t"+part.getEtag());
    // Time when the part was last uploaded
   System.out.println("\t"+part.getLastModified());
}

• Information about a maximum of 1,000 parts can be listed each time. If a task of the specific upload ID contains more than 1,000 parts and ListPartsResult.isTruncated is true in the returned result, not all parts are returned. In such cases, you can use ListPartsResult.getNextPartNumberMarker to obtain the start position for next listing.
• If you want to obtain all parts involved in a specific upload ID, you can use the paging mode for listing.

• Listing all parts

If the number of parts of a multipart upload is larger than 1,000, you can use the following sample code to list all parts.

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
String uploadId = "upload id from initiateMultipartUpload";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

// List the uploaded parts. uploadId is obtained from initiateMultipartUpload.        
ListPartsRequest request = new ListPartsRequest("bucketname", "objectname");
request.setUploadId(uploadId);
ListPartsResult result;

do{
    result = obsClient.listParts(request);
    for(Multipart part : result.getMultipartList()){
    // Part number, specified when uploading
       System.out.println("\t"+part.getPartNumber());
    // Part size
       System.out.println("\t"+part.getSize());
    // Part ETag
       System.out.println("\t"+part.getEtag());
    // Time when the part was last uploaded
       System.out.println("\t"+part.getLastModified());
    }
    request.setPartNumberMarker(Integer.parseInt(result.getNextPartNumberMarker()));
}while(result.isTruncated());

Listing Multipart Uploads

You can call ObsClient.listMultipartUploads to list multipart uploads. The following table describes parameters involved in ObsClient.listMultipartUploads.

• Listing multipart uploads in simple mode

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
String uploadId = "upload id from initiateMultipartUpload";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

ListMultipartUploadsRequest request = new ListMultipartUploadsRequest("bucketname");

MultipartUploadListing result = obsClient.listMultipartUploads(request);
for(MultipartUpload upload : result.getMultipartTaskList()){
    System.out.println("\t" + upload.getUploadId());
    System.out.println("\t" + upload.getObjectKey());
    System.out.println("\t" + upload.getInitiatedDate());
}

• Information about a maximum of 1,000 multipart uploads can be listed each time. If a bucket contains more than 1,000 multipart uploads and MultipartUploadListing.isTruncated is true, not all uploads are listed. In such cases, you can use MultipartUploadListing.getNextKeyMarker and MultipartUploadListing.getNextUploadIdMarker to obtain the start position for next listing.
• If you want to obtain all multipart uploads in a bucket, you can list them in paging mode.

• Listing all multipart uploads in paging mode

String endPoint = "https://your-endpoint";
String ak = "*** Provide your Access Key ***";
String sk = "*** Provide your Secret Key ***";
String uploadId = "upload id from initiateMultipartUpload";
// Create an instance of ObsClient.
ObsClient obsClient = new ObsClient(ak, sk, endPoint);

ListMultipartUploadsRequest request = new ListMultipartUploadsRequest("bucketname");
MultipartUploadListing result;

do{
    result = obsClient.listMultipartUploads(request);
    for(MultipartUpload upload : result.getMultipartTaskList()){
        System.out.println("\t" + upload.getUploadId());
        System.out.println("\t" + upload.getObjectKey());
        System.out.println("\t" + upload.getInitiatedDate());
    }
    request.setKeyMarker(result.getNextKeyMarker());
    request.setUploadIdMarker(result.getNextUploadIdMarker());
}while(result.isTruncated());