# Studentportalen backend-for-frontend (BFF)
## Development instructions
### Prerequisites
- [JDK 24](https://adoptium.net/temurin/releases/?version=24&package=jdk)
- [Docker](https://docs.docker.com/desktop/)
- [Docker Compose](https://docs.docker.com/compose/install/) (v2.24.0 or later)

Start the application with `./mvnw spring-boot:run`. Spring will automatically run the required Docker containers.
The application will be available at http://localhost:8080 and tracing telemetry can be viewed at http://localhost:16686.

If running via some other means start the containers with `docker compose up`.
Activate the Spring Boot profile "development".
Make sure you're using the correct JVM arguments (`--enable-preview`).
Optionally add `-javaagent:opentelemetry-javaagent.jar -Dotel.javaagent.configuration-file=opentelemetry-javaagent.properties`
to enable OpenTelemetry tracing.

### Preview features (`--enable-preview`)
Due to wanting to make many concurrent calls to various backend APIs, preview features have been enabled to gain access
to [Structured Concurrency (JEP 499)](http://openjdk.java.net/jeps/499).
See `src/main/java/se/dsv/studentportalen/bff/TestController.java` for an example of how to use it.
To see it in action browse to http://localhost:8080/test and check the tracing data, and you'll see that the overall
duration is much lower than if the calls were made sequentially.

An alternative would be to use [`CompletableFuture`](https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/util/concurrent/CompletableFuture.html)
but that would require writing Java in a completely different style with a lot of callbacks instead of the
imperative-looking code that Structured Concurrency offers.

## Mocking backend APIs
[Apimposter](https://gitea.dsv.su.se/DMC/apimposter) is used to mock the backend APIs.
The mock data is defined in `src/mock-api`. See the linked documentation for details on how to define the mock data.