Class Blob (2.41.0) 

public class Blob extends BlobInfo

An object in Google Cloud Storage. A Blob object includes the BlobId instance, the set of properties inherited from the BlobInfo class and the Storage instance. The class provides methods to perform operations on the object. Reading a property value does not issue any RPC calls. The object content is not stored within the Blob instance. Operations that access the content issue one or multiple RPC calls, depending on the content size.

Objects of this class are immutable. Operations that modify the blob like #update and #copyTo return a new object. Any changes to the object in Google Cloud Storage made after creation of the Blob are not visible in the Blob. To get a Blob object with the most recent information use #reload.

Example of getting the content of the object in Google Cloud Storage:


 BlobId blobId = BlobId.of(bucketName, blobName);
 Blob blob = storage.get(blobId);
 long size = blob.getSize(); // no RPC call is required
 byte[] content = blob.getContent(); // one or multiple RPC calls will be issued

Inheritance

Object > BlobInfo > Blob

Methods

asBlobInfo()

public BlobInfo asBlobInfo()

Drop the held Storage instance.

Returns
Type Description
BlobInfo

copyTo(BlobId targetBlob, Blob.BlobSourceOption[] options)

public CopyWriter copyTo(BlobId targetBlob, Blob.BlobSourceOption[] options)

Sends a copy request for the current blob to the target blob. Possibly also some of the metadata are copied (e.g. content-type).

Example of copying the blob to a different bucket with a different name.


 String bucketName = "my_unique_bucket";
 String blobName = "copy_blob_name";
 CopyWriter copyWriter = blob.copyTo(BlobId.of(bucketName, blobName));
 Blob copiedBlob = copyWriter.getResult();
Parameters
Name Description
targetBlob BlobId

target blob's id
options BlobSourceOption[]

source blob options
Returns
Type Description
CopyWriter

a CopyWriter object that can be used to get information on the newly created blob or to complete the copy if more than one RPC request is needed

copyTo(String targetBucket, Blob.BlobSourceOption[] options)

public CopyWriter copyTo(String targetBucket, Blob.BlobSourceOption[] options)

Sends a copy request for the current blob to the target bucket, preserving its name. Possibly copying also some of the metadata (e.g. content-type).

Example of copying the blob to a different bucket, keeping the original name.


 String bucketName = "my_unique_bucket";
 CopyWriter copyWriter = blob.copyTo(bucketName);
 Blob copiedBlob = copyWriter.getResult();
Parameters
Name Description
targetBucket String

target bucket's name
options BlobSourceOption[]

source blob options
Returns
Type Description
CopyWriter

a CopyWriter object that can be used to get information on the newly created blob or to complete the copy if more than one RPC request is needed

copyTo(String targetBucket, String targetBlob, Blob.BlobSourceOption[] options)

public CopyWriter copyTo(String targetBucket, String targetBlob, Blob.BlobSourceOption[] options)

Sends a copy request for the current blob to the target blob. Possibly also some of the metadata are copied (e.g. content-type).

Example of copying the blob to a different bucket with a different name.


 String bucketName = "my_unique_bucket";
 String blobName = "copy_blob_name";
 CopyWriter copyWriter = blob.copyTo(bucketName, blobName);
 Blob copiedBlob = copyWriter.getResult();

Example of moving a blob to a different bucket with a different name.


 String destBucket = "my_unique_bucket";
 String destBlob = "move_blob_name";
 CopyWriter copyWriter = blob.copyTo(destBucket, destBlob);
 Blob copiedBlob = copyWriter.getResult();
 boolean deleted = blob.delete();
Parameters
Name Description
targetBucket String

target bucket's name
targetBlob String

target blob's name
options BlobSourceOption[]

source blob options
Returns
Type Description
CopyWriter

a CopyWriter object that can be used to get information on the newly created blob or to complete the copy if more than one RPC request is needed

createAcl(Acl acl)

public Acl createAcl(Acl acl)

Creates a new ACL entry on this blob.

Example of creating a new ACL entry.


 Acl acl = blob.createAcl(Acl.of(User.ofAllAuthenticatedUsers(), Acl.Role.READER));
Parameter
Name Description
acl Acl
Returns
Type Description
Acl

delete(Blob.BlobSourceOption[] options)

public boolean delete(Blob.BlobSourceOption[] options)

Deletes this blob.

Example of deleting the blob, if its generation matches the Blob#getGeneration() value, otherwise a StorageException is thrown.


 boolean deleted = blob.delete(BlobSourceOption.generationMatch());
 if (deleted) {
   // the blob was deleted
 } else {
   // the blob was not found
 }
Parameter
Name Description
options BlobSourceOption[]

blob delete options
Returns
Type Description
boolean

true if blob was deleted, false if it was not found

deleteAcl(Acl.Entity entity)

public boolean deleteAcl(Acl.Entity entity)

Deletes the ACL entry for the specified entity on this blob.

Example of deleting the ACL entry for an entity.


 boolean deleted = blob.deleteAcl(User.ofAllAuthenticatedUsers());
 if (deleted) {
   // the acl entry was deleted
 } else {
   // the acl entry was not found
 }
Parameter
Name Description
entity Acl.Entity
Returns
Type Description
boolean

true if the ACL was deleted, false if it was not found

downloadTo(OutputStream outputStream, Blob.BlobSourceOption[] options)

public void downloadTo(OutputStream outputStream, Blob.BlobSourceOption[] options)

Downloads this blob to the given output stream using specified blob read options. See Also: Storage#downloadTo(BlobId, OutputStream, Storage.BlobSourceOption...)

Parameters
Name Description
outputStream OutputStream
options BlobSourceOption[]

downloadTo(Path path)

public void downloadTo(Path path)

Downloads this blob to the given file path.

This method is replaced with #downloadTo(Path, BlobSourceOption...), but is kept here for binary compatibility with the older versions of the client library.

Parameter
Name Description
path Path

destination

downloadTo(Path path, Blob.BlobSourceOption[] options)

public void downloadTo(Path path, Blob.BlobSourceOption[] options)

Downloads this blob to the given file path using specified blob read options. See Also: Storage#downloadTo(BlobId, Path, Storage.BlobSourceOption...)

Parameters
Name Description
path Path

destination
options BlobSourceOption[]

blob read options

equals(Object obj)

public final boolean equals(Object obj)

Returns true if obj instance Blob.toPb() metadata representation and Blob.options instance of StorageOptions are both equal.

Parameter
Name Description
obj Object
Returns
Type Description
boolean
Overrides

exists(Blob.BlobSourceOption[] options)

public boolean exists(Blob.BlobSourceOption[] options)

Checks if this blob exists.

Example of checking if the blob exists.


 boolean exists = blob.exists();
 if (exists) {
   // the blob exists
 } else {
   // the blob was not found
 }
Parameter
Name Description
options BlobSourceOption[]

blob read options
Returns
Type Description
boolean

true if this blob exists, false otherwise

getAcl(Acl.Entity entity)

public Acl getAcl(Acl.Entity entity)

Returns the ACL entry for the specified entity on this blob or null if not found.

Example of getting the ACL entry for an entity.


 Acl acl = blob.getAcl(User.ofAllAuthenticatedUsers());
Parameter
Name Description
entity Acl.Entity
Returns
Type Description
Acl

getContent(Blob.BlobSourceOption[] options)

public byte[] getContent(Blob.BlobSourceOption[] options)

Returns this blob's content.

Example of reading all bytes of the blob, if its generation matches the Blob#getGeneration() value, otherwise a StorageException is thrown.


 byte[] content = blob.getContent(BlobSourceOption.generationMatch());
Parameter
Name Description
options BlobSourceOption[]

blob read options
Returns
Type Description
byte[]

getStorage()

public Storage getStorage()

Returns the blob's Storage object used to issue requests.

Returns
Type Description
Storage

hashCode()

public final int hashCode()
Returns
Type Description
int
Overrides

listAcls()

public List<Acl> listAcls()

Lists the ACL entries for this blob.

Example of listing the ACL entries.


 List<Acl> acls = blob.listAcls();
 for (Acl acl : acls) {
   // do something with ACL entry
 }
Returns
Type Description
List<Acl>

reader(Blob.BlobSourceOption[] options)

public ReadChannel reader(Blob.BlobSourceOption[] options)

Returns a ReadChannel object for reading this blob's content.

Example of reading the blob's content through a reader.


 try (ReadChannel reader = blob.reader()) {
   ByteBuffer bytes = ByteBuffer.allocate(64 * 1024);
   while (reader.read(bytes) > 0) {
     bytes.flip();
     // do something with bytes
     bytes.clear();
   }
 }

Example of reading just a portion of the blob's content.


 int start = 1;
 int end = 8;
 try (ReadChannel reader = blob.reader()) {
   reader.seek(start);
   ByteBuffer bytes = ByteBuffer.allocate(end - start);
   reader.read(bytes);
   return bytes.array();
 }
Parameter
Name Description
options BlobSourceOption[]

blob read options
Returns
Type Description
com.google.cloud.ReadChannel

reload(Blob.BlobSourceOption[] options)

public Blob reload(Blob.BlobSourceOption[] options)

Fetches the latest blob properties. Returns null if the blob no longer exists.

options parameter can contain the preconditions. For example, the user might want to get the blob properties only if the content has not been updated externally. StorageException with the code 412 is thrown if preconditions fail.

Example of retrieving the blob's latest information only if the content is not updated externally:


 Blob blob = storage.get(BlobId.of(bucketName, blobName));

 doSomething();

 try {
   blob = blob.reload(Blob.BlobSourceOption.generationMatch());
 } catch (StorageException e) {
   if (e.getCode() == 412) {
     // the content was updated externally
   } else {
     throw e;
   }
 }
Parameter
Name Description
options BlobSourceOption[]

preconditions to use on reload, see https://cloud.google.com/storage/docs/json_api/v1/objects/get for more information.
Returns
Type Description
Blob

a Blob object with latest information or null if no longer exists.

signUrl(long duration, TimeUnit unit, Storage.SignUrlOption[] options)

public URL signUrl(long duration, TimeUnit unit, Storage.SignUrlOption[] options)

Generates a signed URL for this blob. If you want to allow access for a fixed amount of time to this blob, you can use this method to generate a URL that is only valid within a certain time period. This is particularly useful if you don't want publicly accessible blobs, but also don't want to require users to explicitly log in. Signing a URL requires a service account signer. If an instance of com.google.auth.ServiceAccountSigner was passed to StorageOptions' builder via setCredentials(Credentials) or the default credentials are being used and the environment variable GOOGLE_APPLICATION_CREDENTIALS is set or your application is running in App Engine, then signUrl will use that credentials to sign the URL. If the credentials passed to StorageOptions do not implement ServiceAccountSigner (this is the case, for instance, for Compute Engine credentials and Google Cloud SDK credentials) then signUrl will throw an IllegalStateException unless an implementation of ServiceAccountSigner is passed using the SignUrlOption#signWith(ServiceAccountSigner) option.

A service account signer is looked for in the following order:

  1. The signer passed with the option SignUrlOption#signWith(ServiceAccountSigner)
  2. The credentials passed to StorageOptions
  3. The default credentials, if no credentials were passed to StorageOptions

Example of creating a signed URL for the blob that is valid for 2 weeks, using the default credentials for signing the URL:


 URL signedUrl = blob.signUrl(14, TimeUnit.DAYS);

Example of creating a signed URL for the blob passing the SignUrlOption#signWith(ServiceAccountSigner) option, that will be used to sign the URL:


 String keyPath = "/path/to/key.json";
 URL signedUrl = blob.signUrl(14, TimeUnit.DAYS, SignUrlOption.signWith(
     ServiceAccountCredentials.fromStream(new FileInputStream(keyPath))));

Example of creating a signed URL for a blob generation:


 URL signedUrl = blob.signUrl(1, TimeUnit.HOURS,
     SignUrlOption.withQueryParams(ImmutableMap.of("generation", "1576656755290328")));

See Also: Signed-URLs

Parameters
Name Description
duration long

time until the signed URL expires, expressed in unit. The finer granularity supported is 1 second, finer granularities will be truncated
unit TimeUnit

time unit of the duration parameter
options SignUrlOption[]

optional URL signing options
Returns
Type Description
URL

a signed URL for this blob and the specified options

toBuilder()

public Blob.Builder toBuilder()

Returns a builder for the current blob.

Returns
Type Description
Blob.Builder
Overrides

update(Storage.BlobTargetOption[] options)

public Blob update(Storage.BlobTargetOption[] options)

Updates the blob properties. The options parameter contains the preconditions for applying the update. To update the properties call #toBuilder(), set the properties you want to change, build the new Blob instance, and then call #update(BlobTargetOption...).

The property update details are described in Storage#update(BlobInfo). Storage#update(BlobInfo, BlobTargetOption...) describes how to specify preconditions.

Example of updating the content type:


 BlobId blobId = BlobId.of(bucketName, blobName);
 Blob blob = storage.get(blobId);
 blob.toBuilder().setContentType("text/plain").build().update();

See Also: https://cloud.google.com/storage/docs/json_api/v1/objects/update

Parameter
Name Description
options BlobTargetOption[]

preconditions to apply the update
Returns
Type Description
Blob

the updated Blob

updateAcl(Acl acl)

public Acl updateAcl(Acl acl)

Updates an ACL entry on this blob.

Example of updating a new ACL entry.


 Acl acl = blob.updateAcl(Acl.of(User.ofAllAuthenticatedUsers(), Acl.Role.OWNER));
Parameter
Name Description
acl Acl
Returns
Type Description
Acl

writer(Storage.BlobWriteOption[] options)

public WriteChannel writer(Storage.BlobWriteOption[] options)

Returns a WriteChannel object for writing to this blob. By default any md5 and crc32c values in the current blob are ignored unless requested via the BlobWriteOption.md5Match and BlobWriteOption.crc32cMatch options.

Example of writing the blob's content through a writer.


 byte[] content = "Hello, World!".getBytes(UTF_8);
 try (WriteChannel writer = blob.writer()) {
     writer.write(ByteBuffer.wrap(content, 0, content.length));
 } catch (IOException ex) {
   // handle exception
 }
 blob = blob.reload();
Parameter
Name Description
options BlobWriteOption[]

target blob options
Returns
Type Description
com.google.cloud.WriteChannel