readme.md

Spring Data Reactive Demo

A very small demo Application showing various aspects of Spring Data reactive support. You can walk through the commits one by one to see the application evolve.

What's it all about

The application is supposed to store, retrieve and expose Persons from an embedded MongoDB instance in a non blocking way.

Step 1: Setup some test data

Nothing fancy in here - we just aim to create a Stream of Person objects randomly named after characters from Game of Thrones.

String[] names = { "Eddard", "Catelyn", "Jon", "Rob", "Sansa", "Aria", "Bran", "Rickon" };

Flux<Person> starks = Flux
    .fromStream(Stream.generate(() -> names[ramdom.nextInt(names.length - 1)]).map(Person::new));

Step 2:

Set up a ReactiveCrudRepository for MongoDB and store a new Person from the Stream each and every second.

Flux.interval(Duration.ofSeconds(1))
	.zipWith(starks)
	.map(Tuple2::getT2)
	.flatMap(repository::save)
	.subscribe();

interface PersonRepository extends ReactiveCrudRepository<Person, String> {}

Step 3:

Create a simple derived finder method and expose the result via Spring WebFlux.

@RestController
@RequiredArgsConstructor
static class PersonController {

	final PersonRepository repository;

	@GetMapping("/") // curl localhost:8080/?name=Eddard
	Flux<Person> fluxPersons(String name) {
		return repository.findAllByName(name);
	}
}

interface PersonRepository extends ReactiveCrudRepository<Person, String> {

	Flux<Person> findAllByName(String name);
}

Step 4

Use StepVerifier from reactor-test for creating unit and integration tests for the application.

@Test
public void saveAndFindAll() {

	StepVerifier.create(repository.save(new Person("Aria")))
		.expectNextCount(1)
		.verifyComplete();

	StepVerifier.create(repository.findAllByName("Aria").take(1))
		.consumeNextWith(value -> Assert.assertTrue(value.getName().equals("Aria")))
		.verifyComplete();
}

Step 5

Use RxJava Observable instead of Reactor Flux for reading and exposing data.

@GetMapping("/rx") // curl localhost:8080/rx?name=Eddard
Observable<Person> rxPersons(String name) {
	return repository.findByName(name);
}

interface PersonRepository extends ReactiveCrudRepository<Person, String> {

	//...

	Observable<Person> findByName(String name);
}

Step 6

Use MongoDB capped collections and tailable cursors to create an infinite stream.

@GetMapping(value = "/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE) // curl localhost:8080/stream
Flux<Person> streamPersons() {
	return repository.findBy();
}

interface PersonRepository extends ReactiveCrudRepository<Person, String> {

	//...

	@Tailable
	Flux<Person> findBy();
}

Step 7

Transition to a more functional style routing declaration using RouterFunctions.

@Bean
RouterFunction<ServerResponse> routerFunction(PersonHandler requestHandler) {

	return RouterFunctions
		.route(RequestPredicates.GET("/"), requestHandler::fluxPersons)
		.andRoute(RequestPredicates.GET("/rx"), requestHandler::rxPersons)
		.andRoute(RequestPredicates.GET("/stream"), requestHandler::streamPersons);
}

@Component
@RequiredArgsConstructor
static class PersonHandler {

	final PersonRepository personRepository;

	Mono<ServerResponse> fluxPersons(ServerRequest request) {

		return ServerResponse.ok()
			.body(personRepository.findAllByName(request.queryParam("name").orElse("")), Person.class);
	}

	Mono<ServerResponse> rxPersons(ServerRequest request) {

		return ServerResponse.ok()
			.body(new PublisherAdapter(personRepository.findByName(request.queryParam("name").orElse(""))), Person.class);
	}

	Mono<ServerResponse> streamPersons(ServerRequest request) {

		return ServerResponse.ok()
			.contentType(MediaType.TEXT_EVENT_STREAM)
			.body(personRepository.findBy(), Person.class);
	}
}

Step 8

Consume data from remote service using WebClient.

@Bean
WebClient client() {
	return WebClient.create("http://localhost:8080/");
}

@Bean
CommandLineRunner run(WebClient client) {

	return (args) -> {

		client.get()
			.uri(builder -> builder.path("/").queryParam("name", "Eddard").build())
			.retrieve()
			.bodyToFlux(Person.class)
			.subscribe(System.out::println);
	};
}