Use the Micronaut Object Storage API to store files in Oracle Cloud Infrastructure (OCI) Object Storage

Learn how to upload and retrieve files from Oracle Cloud Infrastructure (OCI) Object Storage using the Micronaut Object Storage API

Authors: Álvaro Sánchez-Mariscal

Micronaut Version: 4.5.0

1. Getting Started

In this guide, we will create a Micronaut application written in Java.

It will be a microservice to store, retrieve and delete profile pictures for users.

2. What you will need

To complete this guide, you will need the following:

Some of the following commands use jq

jq is a lightweight and flexible command-line JSON processor

3. Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

4. Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide \
    --features=yaml,object-storage-oracle-cloud,graalvm \
    --build=maven \
    --lang=java \
If you don’t specify the --build argument, Gradle is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.
If you don’t specify the --test argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

If you use Micronaut Launch, select Micronaut Application as application type and add yaml, object-storage-oracle-cloud, and graalvm features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application.

5. Create a bucket

5.1. Compartment OCID

Find the OCID of the compartment where we’ll be deploying. Run this to list all the compartments in your root compartment:

oci iam compartment list

and find the compartment by the name or description in the JSON output. It should look like this:

  "compartment-id": "ocid1.tenancy.oc1..aaaaaaaaud4g4e5ovjaw...",
  "defined-tags": {},
  "description": "Micronaut guides",
  "freeform-tags": {},
  "id": "ocid1.compartment.oc1..aaaaaaaarkh3s2wcxbbm...",
  "inactive-status": null,
  "is-accessible": null,
  "lifecycle-state": "ACTIVE",
  "name": "micronaut-guides",
  "time-created": "2021-05-02T23:54:28.392000+00:00"

Use the OCID from the id property; the compartment-id property is the parent compartment.

For convenience, save the compartment OCID as an environment variable. For Linux or Mac, run

export C=ocid1.compartment.oc1..aaaaaaaarkh3s2wcxbbm...

or for Windows, if using cmd run

set C=ocid1.compartment.oc1..aaaaaaaarkh3s2wcxbbm...

and if using PowerShell run

$C = "ocid1.compartment.oc1..aaaaaaaarkh3s2wcxbbm..."
In the examples below we use Linux/Mac syntax for environment variables, e.g. -c $C. If you use Windows cmd, change those to -c %C% (but no change needed if using PowerShell)

5.2. Use the CLI to create the bucket

oci os bucket create --compartment-id $C --name micronaut-guide-object-storage

We can also use the CLI to get the Object Storage namespace:

export OCI_NS=$(oci os ns get | jq -r '.data')

Then, configure the bucket name and namespace in application.yml:

        bucket: micronaut-guide-object-storage
        namespace: ${OCI_NS}

6. Controller API

Let’s define an interface with the endpoints of the profile pictures microservice:

public interface ProfilePicturesApi {

    @Post(uri = "/{userId}", consumes = MediaType.MULTIPART_FORM_DATA) (1)
    HttpResponse upload(CompletedFileUpload fileUpload, String userId, HttpRequest<?> request);

    @Get("/{userId}") (2)
    Optional<HttpResponse<StreamedFile>> download(String userId);

    @Status(HttpStatus.NO_CONTENT) (3)
    @Delete("/{userId}") (4)
    void delete(String userId);
1 The @Post annotation maps the method to an HTTP POST request.
2 The @Get annotation maps the method to an HTTP GET request.
3 You can return void in your controller’s method and specify the HTTP status code via the @Status annotation.
4 The @Delete annotation maps the delete method to an HTTP Delete request on /{userId}.

And then, an implementation with the required dependencies:

@Controller(ProfilePicturesController.PREFIX) (1)
@ExecuteOn(TaskExecutors.BLOCKING) (2)
public class ProfilePicturesController implements ProfilePicturesApi {

    static final String PREFIX = "/pictures";

    private final OracleCloudStorageOperations objectStorage; (3)
    private final HttpHostResolver httpHostResolver; (4)

    public ProfilePicturesController(OracleCloudStorageOperations objectStorage, HttpHostResolver httpHostResolver) {
        this.objectStorage = objectStorage;
        this.httpHostResolver = httpHostResolver;

1 The class is defined as a controller with the @Controller annotation mapped to the path /pictures.
2 It is critical that any blocking I/O operations (such as fetching the data from the database) are offloaded to a separate thread pool that does not block the Event loop.
3 OracleCloudStorageOperations is the cloud-specific interface for using object storage.
4 HttpHostResolver allows you to resolve the host for an HTTP

6.1. Upload endpoint

Implement the upload endpoint by receiving the file from the HTTP client via CompletedFileUpload, and the userId path parameter. Upload it to Oracle Cloud using OracleCloudStorageOperations, and then return its ETag in an HTTP response header to the client:

public HttpResponse<?> upload(CompletedFileUpload fileUpload, String userId, HttpRequest<?> request) {
    String key = buildKey(userId); (1)
    UploadRequest objectStorageUpload = UploadRequest.fromCompletedFileUpload(fileUpload, key); (2)
    UploadResponse<PutObjectResponse> response = objectStorage.upload(objectStorageUpload);  (3)

    return HttpResponse
            .created(location(request, userId)) (4)
            .header(HttpHeaders.ETAG, response.getETag()); (5)

private static String buildKey(String userId) {
    return userId + ".jpg";

private URI location(HttpRequest<?> request, String userId) {
    return UriBuilder.of(httpHostResolver.resolve(request))
1 The key represents the path under which the file will be stored.
2 You can use any of the UploadRequest static methods to build an upload request.
3 The upload operation returns an UploadResponse, which wraps the cloud-specific SDK response
4 We return the absolute URL of the resource in the Location header.
5 The response object contains some common properties for all cloud vendors, such as the ETag, that is sent in a header to the client.

6.2. Download endpoint

For the download endpoint, simply retrieve the entry from the expected key, and transform it into an StreamedFile:

public Optional<HttpResponse<StreamedFile>> download(String userId) {
    String key = buildKey(userId);
    return objectStorage.retrieve(key) (1)
            .map(ProfilePicturesController::buildStreamedFile); (2)

private static HttpResponse<StreamedFile> buildStreamedFile(OracleCloudStorageEntry entry) {
    GetObjectResponse nativeEntry = entry.getNativeEntry();
    MediaType mediaType = MediaType.of(nativeEntry.getContentType());
    StreamedFile file = new StreamedFile(entry.getInputStream(), mediaType).attach(entry.getKey());
    MutableHttpResponse<Object> httpResponse = HttpResponse.ok()
            .header(HttpHeaders.ETAG, nativeEntry.getETag()); (3)
    return httpResponse.body(file);
1 The retrieve operation returns an ObjectStorageEntry, in this case an OracleCloudStorageEntry, which allows accessing the Oracle Cloud-specific GetObjectResponse
2 We transform the OracleCloudStorageEntry into an HttpResponse<StreamedFile>.
3 The response contains not only the file, but also an ETag header.
The HTTP client could have used the ETag from the upload operation and send it in a If-None-Match header in the download request to implement caching, which then would have been to be implemented in the download endpoint. But this is beyond the scope of this guide.

6.3. Delete endpoint

For the delete endpoint, all we have to do is invoke the delete method with the expected key:

public void delete(String userId) {
    String key = buildKey(userId);

7. Running the Application

To run the application, use the ./mvnw mn:run command, which starts the application on port 8080.

8. Generate a Micronaut Application Native Executable with GraalVM

We will use GraalVM, the polyglot embeddable virtual machine, to generate a native executable of our Micronaut application.

Compiling native executables ahead of time with GraalVM improves startup time and reduces the memory footprint of JVM-based applications.

Only Java and Kotlin projects support using GraalVM’s native-image tool. Groovy relies heavily on reflection, which is only partially supported by GraalVM.

8.1. GraalVM installation

The easiest way to install GraalVM on Linux or Mac is to use

Java 17
sdk install java 17.0.8-graal
Java 17
sdk use java 17.0.8-graal

For installation on Windows, or for manual installation on Linux or Mac, see the GraalVM Getting Started documentation.

The previous command installs Oracle GraalVM, which is free to use in production and free to redistribute, at no cost, under the GraalVM Free Terms and Conditions.

Alternatively, you can use the GraalVM Community Edition:

Java 17
sdk install java 17.0.8-graalce
Java 17
sdk use java 17.0.8-graalce

8.2. Native executable generation

To generate a native executable using Maven, run:

./mvnw package -Dpackaging=native-image

The native executable is created in the target directory and can be run with target/micronautguide.

9. Testing

Test the application from the command line.

9.1. Uploading a profile picture

If you want to upload a file larger than 1MB, you need to configure:

      max-file-size: 20971520 # 20 * 1024 * 1024 = 20MB

Assuming you have locally a profile picture in a profile.jpg file, you can send it to your application with:

$ curl -i -F 'fileUpload=@profile.jpg' http://localhost:8080/pictures/alvaro

HTTP/1.1 201 Created
location: http://localhost:8080/pictures/alvaro
ETag: "617cb82e296e153c29b34cccf7af0908"
date: Wed, 14 Sep 2022 12:50:30 GMT
connection: keep-alive
transfer-encoding: chunked

Note the Location and ETag headers.

Use the oci CLI to verify that the file has been uploaded to an Oracle Cloud bucket:

oci os object list --bucket-name micronaut-guide-object-storage

9.2. Download a profile picture

curl http://localhost:8080/pictures/alvaro -O -J

The file will be saved as alvaro.jpg since our download endpoint includes a Content-Disposition: attachment header. Open it to check that it is actually the same image as profile.jpg.

9.3. Delete a profile picture

curl -X DELETE http://localhost:8080/pictures/alvaro

Then, check that the file has actually been deleted:

oci os object list --bucket-name micronaut-guide-object-storage

9.4. Cleanup

Remove the bucket from Oracle Cloud to not leave stale resources:

oci os bucket delete --bucket-name micronaut-guide-object-storage

11. License

All guides are released with an Apache license 2.0 license for the code and a Creative Commons Attribution 4.0 license for the writing and media (images…​).