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custom_content: |
#### Creating an authorized service object
To make authenticated requests to Google Cloud Storage, you must create a service object with credentials. You can
then make API calls by calling methods on the Storage service object. The simplest way to authenticate is to use
[Application Default Credentials](https://developers.google.com/identity/protocols/application-default-credentials).
These credentials are automatically inferred from your environment, so you only need the following code to create your
service object:
```java
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
Storage storage = StorageOptions.getDefaultInstance().getService();
```
For other authentication options, see the [Authentication](https://github.com/googleapis/google-cloud-java#authentication) page in Google Cloud Java.
#### Storing data
Stored objects are called "blobs" in `google-cloud` and are organized into containers called "buckets". `Blob`, a
subclass of `BlobInfo`, adds a layer of service-related functionality over `BlobInfo`. Similarly, `Bucket` adds a
layer of service-related functionality over `BucketInfo`. In this code snippet, we will create a new bucket and
upload a blob to that bucket.
Add the following imports at the top of your file:
```java
import static java.nio.charset.StandardCharsets.UTF_8;
import com.google.cloud.storage.Blob;
import com.google.cloud.storage.Bucket;
import com.google.cloud.storage.BucketInfo;
```
Then add the following code to create a bucket and upload a simple blob.
*Important: Bucket names have to be globally unique (among all users of Cloud Storage). If you choose a bucket name
that already exists, you'll get a helpful error message telling you to choose another name. In the code below, replace
"my_unique_bucket" with a unique bucket name. See more about naming rules
[here](https://cloud.google.com/storage/docs/bucket-naming?hl=en#requirements).*
```java
// Create a bucket
String bucketName = "my_unique_bucket"; // Change this to something unique
Bucket bucket = storage.create(BucketInfo.of(bucketName));
// Upload a blob to the newly created bucket
BlobId blobId = BlobId.of(bucketName, "my_blob_name");
BlobInfo blobInfo = BlobInfo.newBuilder(blobId).setContentType("text/plain").build();
Blob blob = storage.create(blobInfo, "a simple blob".getBytes(UTF_8));
```
A complete example for creating a blob can be found at
[UploadObject.java](https://github.com/googleapis/java-storage/blob/main/samples/snippets/src/main/java/com/example/storage/object/UploadObject.java).
At this point, you will be able to see your newly created bucket and blob on the Google Developers Console.
#### Retrieving data
Now that we have content uploaded to the server, we can see how to read data from the server. Add the following line
to your program to get back the blob we uploaded.
```java
BlobId blobId = BlobId.of(bucketName, "my_blob_name");
byte[] content = storage.readAllBytes(blobId);
String contentString = new String(content, UTF_8);
```
A complete example for accessing blobs can be found at
[DownloadObject.java](https://github.com/googleapis/java-storage/blob/main/samples/snippets/src/main/java/com/example/storage/object/DownloadObject.java).
#### Updating data
Another thing we may want to do is update a blob. The following snippet shows how to update a Storage blob if it exists.
``` java
BlobId blobId = BlobId.of(bucketName, "my_blob_name");
Blob blob = storage.get(blobId);
if (blob != null) {
byte[] prevContent = blob.getContent();
System.out.println(new String(prevContent, UTF_8));
WritableByteChannel channel = blob.writer();
channel.write(ByteBuffer.wrap("Updated content".getBytes(UTF_8)));
channel.close();
}
```
#### Listing buckets and contents of buckets
Suppose that you've added more buckets and blobs, and now you want to see the names of your buckets and the contents
of each one. Add the following code to list all your buckets and all the blobs inside each bucket.
```java
// List all your buckets
System.out.println("My buckets:");
for (Bucket bucket : storage.list().iterateAll()) {
System.out.println(bucket);
// List all blobs in the bucket
System.out.println("Blobs in the bucket:");
for (Blob blob : bucket.list().iterateAll()) {
System.out.println(blob);
}
}
```
#### Complete source code
See [ListObjects.java](https://github.com/googleapis/java-storage/blob/main/samples/snippets/src/main/java/com/example/storage/object/ListObjects.java) for a complete example.
### Example Applications
- [`Bookshelf`](https://github.com/GoogleCloudPlatform/getting-started-java/tree/main/bookshelf) - An App Engine application that manages a virtual bookshelf.
- This app uses `google-cloud` to interface with Cloud Datastore and Cloud Storage. It also uses Cloud SQL, another Google Cloud Platform service.
- [`Flexible Environment/Storage example`](https://github.com/GoogleCloudPlatform/java-docs-samples/tree/main/flexible/cloudstorage) - An app that uploads files to a public Cloud Storage bucket on the App Engine Flexible Environment runtime.
versioning: |
This library follows [Semantic Versioning](http://semver.org/), but does update [Storage interface](src/main/java/com.google.cloud.storage/Storage.java)
to introduce new methods which can break your implementations if you implement this interface for testing purposes.