quarkus

Defining a REST Client

• Create an interface annotated with @RegisterRestClient and JAX-RS annotations.
• Use @Path, @GET, @POST, etc. on methods to define the API contract.
• Return types can be plain objects (Jackson/JSON-B auto-serialized), Uni<T> for reactive, or Response.

Configuration

• Set the base URL via config: quarkus.rest-client."com.example.MyClient".url=http://api.example.com
• Or use configKey: @RegisterRestClient(configKey = "my-api") then quarkus.rest-client.my-api.url=...
• Timeouts: quarkus.rest-client.my-api.connect-timeout=5000 and read-timeout.

Injection and Usage

• Inject with @RestClient MyClient client — no @Inject needed, even if supported.
• The client is a CDI bean — use it in any CDI-managed class.

Error Handling

• Implement ResponseExceptionMapper<T> to convert error responses to exceptions.
• Register with @RegisterProvider(MyExceptionMapper.class) on the client interface.

Testing

• Use @InjectMock @RestClient to mock the client in tests.
• Alternatively, use WireMock to simulate the remote API.
• For integration tests, point the client URL to a test server.

Common Pitfalls

• Do NOT forget to set the URL in config — the client will fail at injection time if missing.
• REST Client uses the REST Reactive stack — do NOT combine with RESTEasy Classic client.
• Always set reasonable timeouts for production use.