153. Spring Resources

Spring Resources are an abstraction for a number of low-level resources, such as file system files, classpath files, servlet context-relative files, etc. Spring Cloud GCP adds a new resource type: a Google Cloud Storage (GCS) object.

A Spring Boot starter is provided to auto-configure the various Storage components.

Maven coordinates, using Spring Cloud GCP BOM:

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-gcp-starter-storage</artifactId>
</dependency>

Gradle coordinates:

dependencies {
    compile group: 'org.springframework.cloud', name: 'spring-cloud-gcp-starter-storage'
}

This starter is also available from Spring Initializr through the GCP Storage entry.

153.1 Google Cloud Storage

The Spring Resource Abstraction for Google Cloud Storage allows GCS objects to be accessed by their GCS URL using the @Value annotation:

@Value("gs://[YOUR_GCS_BUCKET]/[GCS_FILE_NAME]")
private Resource gcsResource;

…​or the Spring application context

SpringApplication.run(...).getResource("gs://[YOUR_GCS_BUCKET]/[GCS_FILE_NAME]");

This creates a Resource object that can be used to read the object, among other possible operations.

It is also possible to write to a Resource, although a WriteableResource is required.

@Value("gs://[YOUR_GCS_BUCKET]/[GCS_FILE_NAME]")
private Resource gcsResource;
...
try (OutputStream os = ((WritableResource) gcsResource).getOutputStream()) {
  os.write("foo".getBytes());
}

To work with the Resource as a Google Cloud Storage resource, cast it to GoogleStorageResource.

If the resource path refers to an object on Google Cloud Storage (as opposed to a bucket), then the getBlob method can be called to obtain a Blob. This type represents a GCS file, which has associated metadata, such as content-type, that can be set. The createSignedUrl method can also be used to obtain signed URLs for GCS objects. However, creating signed URLs requires that the resource was created using service account credentials.

The Spring Boot Starter for Google Cloud Storage auto-configures the Storage bean required by the spring-cloud-gcp-storage module, based on the CredentialsProvider provided by the Spring Boot GCP starter.

153.1.1 Setting the Content Type

You can set the content-type of Google Cloud Storage files from their corresponding Resource objects:

((GoogleStorageResource)gcsResource).getBlob().toBuilder().setContentType("text/html").build().update();

153.2 Configuration

The Spring Boot Starter for Google Cloud Storage provides the following configuration options:

Name

Description

Required

Default value

spring.cloud.gcp.storage.enabled

Enables the GCP storage APIs.

No

true

spring.cloud.gcp.storage.auto-create-files

Creates files and buckets on Google Cloud Storage when writes are made to non-existent files

No

true

spring.cloud.gcp.storage.credentials.location

OAuth2 credentials for authenticating with the Google Cloud Storage API, if different from the ones in the Spring Cloud GCP Core Module

No

 

spring.cloud.gcp.storage.credentials.encoded-key

Base64-encoded contents of OAuth2 account private key for authenticating with the Google Cloud Storage API, if different from the ones in the Spring Cloud GCP Core Module

No

 

spring.cloud.gcp.storage.credentials.scopes

OAuth2 scope for Spring Cloud GCP Storage credentials

No

https://www.googleapis.com/auth/devstorage.read_write

153.3 Sample

A sample application and a codelab are available.