The document introduces Micronaut, a lightweight framework designed for building reactive microservices and cloud applications, emphasizing its compile-time dependency injection and performance efficiency. It covers features such as bean management, AOP, reactive programming, and serverless function support, alongside practical examples of HTTP clients and routing. The document also highlights the framework's minimal resource consumption compared to alternatives like Spring and Grails.

1. Reactive microservices
with Micronaut
Álvaro Sánchez-Mariscal
@alvaro_sanchez

2. About me
— Developer since 2001.
— Founded Salenda in 2007.
— Grails user since v0.4.
— Working @ OCI since 2015.
— Father since 2017!
!
@alvaro_sanchez

3. DISCLAIMER
!
Work in progress

4. Introducing

5. Introducing Micronaut
The productivity of Grails with the performance
of a compile-time, non-blocking framework.
— Designed from the ground up with microservices and the
cloud in mind.
— Ultra-lightweight and Reactive (based on Netty)
— Integrated AOP and Compile-Time DI for Java and Groovy.
— HTTP Client & Server.
@alvaro_sanchez

6. Reactive microservices
— Any Reactive Streams implementation:
— RxJava 2.x.
— Reactor 3.x.
— Akka.
— Plain old java.util.concurrent.CompletableFuture.
@alvaro_sanchez

7. Micronaut is small and fast!
— JAR files: 8Mb (Java) / 12Mb (Groovy).
— Spring+Groovy: 36MB / Grails: 27Mb.
— Heap size: 7Mb (Java) / 19Mb (Groovy).
— Spring+Groovy: 33Mb / Grails: 49Mb.
— Startup time: ~1 second.
— Spring / Grails: ~3-4 seconds.
@alvaro_sanchez

8. Features

9. Inversion of Control
Dependency Injection

10. Inversion of Control /
Dependency Injection
— Inspired from Spring.
— Compile-time: no reflection, no runtime proxies.
— JSR-330 (javax.inject) or Spring-like annotations.
— Implemented via annotation processors (Java) and
AST transformations (Groovy) that use ASM to
generate bytecode.
@alvaro_sanchez

11. interface Engine {
String start()
}
@Singleton
class V8Engine implements Engine {
String start() {
"Starting V8"
}
}
@Singleton
class Vehicle {
final Engine engine
@Inject Vehicle(Engine engine) {
this.engine = engine
}
String start() {
engine.start() // "Starting V8"
}
}
@alvaro_sanchez

12. Implicit injection via constructor
@Singleton
class WeatherService {}
@Controller('/weather')
class WeatherController {
final WeatherService weatherService
WeatherController(WeatherService weatherService) {
this.weatherService = weatherService
}
}
@alvaro_sanchez

13. Injectable types
— An Optional of a bean. If the bean doesn’t exist
empty() is injected. Alternatively, use @Nullable.
— An Iterable or subtype of Iterable (eg List, Collection
etc).
— A lazy Stream of beans.
— A native array of beans of a given type (Engine[]).
— A javax.inject.Provider if a circular dependency
requires it.
@alvaro_sanchez

14. Bean qualifiers
@Singleton
class V6Engine implements Engine { ... }
@Singleton
class V8Engine implements Engine { ... }
//Vehicle constructor
@Inject Vehicle(@Named('v8') Engine engine) {
this.engine = engine
}
@alvaro_sanchez

15. Bean qualifiers
@Qualifier
@Retention(RUNTIME)
@interface V8 {
}
//Vehicle constructor
@Inject Vehicle(@V8 Engine engine) {
this.engine = engine
}
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16. Refreshable beans
@Refreshable
class WeatherService {
String forecast
@PostConstruct
void init() {
forecast = "Scattered Clouds ${new Date().format('dd/MMM/yy HH:ss.SSS')}"
}
String latestForecast() {
return forecast
}
}
@alvaro_sanchez

17. Refreshable beans
@Controller('/weather')
class WeatherController {
@Inject
WeatherService weatherService
...
}
— Refreshable via:
— The /refresh endpoint.
— applicationContext.publishEvent(new RefreshEvent())
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18. Refreshing upon config
changes
@Bean(preDestroy = "close")
@Refreshable('mongodb')
MongoClient mongoClient(ReactiveMongoConfiguration rmc) {
return MongoClients.create(rmc.buildSettings())
}
@alvaro_sanchez

19. Bean factories
@Singleton
class CrankShaft {}
@Factory
class EngineFactory {
@Bean
@Singleton
Engine v8Engine(CrankShaft crankShaft) {
new V8Engine(crankShaft)
}
}
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20. Conditional beans
@Singleton
@Requires(beans = DataSource)
@Requires(property = "datasource.url")
class JdbcBookService implements BookService {
DataSource dataSource
public JdbcBookService(DataSource dataSource) {
this.dataSource = dataSource
}
}
@alvaro_sanchez

21. Conditional beans
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PACKAGE, ElementType.TYPE})
@Requires(beans = DataSource)
@Requires(property = "datasource.url")
@interface RequiresJdbc {
}
@RequiresJdbc
class JdbcBookService implements BookService {
...
}
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22. Supported conditions
— @Requires(classes=javax.servlet.Servlet)
— @Requires(beans=javax.sql.DataSource)
— @Requires(env='TRAVIS')
— @Requires(configuration='foo.bar')
— @Requires(sdk=Sdk.JAVA, value="1.8")
— @Requires(property='consul.enabled', value="true",
defaultValue="false")
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23. Bean configurations
— Grouping of multiple bean definitions within a
package:
//file: src/main/groovy/com/example/json/package-info.groovy
@Configuration
@Requires(classes = com.fasterxml.jackson.databind.ObjectMapper)
package com.example.json
— All the beans from the package can be required with
@Requires(configuration='com.example.json')
@alvaro_sanchez

24. Life-cycle methods and events
— javax.annotation.PostConstruct is supported.
— For events:
@Singleton
class EngineInitializer implements BeanInitializedEventListener<EngineFactory> {
@Override
EngineFactory onInitialized(BeanInitializingEvent<EngineFactory> event) {
EngineFactory engineFactory = event.bean
engineFactory.rodLength = 6.6
return event.bean
}
}
@alvaro_sanchez

25. Application configuration

26. PropertySources
— Command line arguments.
— Properties from SPRING_APPLICATION_JSON (for Spring compatibility).
— Properties from MICRONAUT_APPLICATION_JSON.
— Java System Properties.
— OS environment variables.
— Enviroment-specific properties from application-{environment}.
{extension}.
— (Either .properties, .json, .yml or .groovy formats supported)
— Application-specific properties from application.{extension}.
@alvaro_sanchez

27. Injecting configuration values
@Singleton
class EngineImpl implements Engine {
@Value('${my.engine.cylinders:6}')
int cylinders
}
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28. @EachProperty
@EachProperty("myapp.datasources")
public class DataSourceConfiguration {
final String name
final URI url
}
//src/main/resources/application.properties
myapp.datasources.one = "jdbc:mysql://localhost/one"
myapp.datasources.two = "jdbc:mysql://localhost/two"
@alvaro_sanchez

29. @EachBean
@Factory
class DataSourceFactory {
@EachBean(DataSourceConfiguration)
DataSource dataSource(DataSourceConfiguration cfg) {
URI url = cfg.url
return new DataSource(url)
}
}
@alvaro_sanchez

30. Type-safe @ConfigurationProperties
@ConfigurationProperties('my.engine')
class EngineConfig {
@NotBlank
String manufacturer = "Ford"
@Min(1L)
int cylinders
CrankShaft crankShaft = new CrankShaft()
@ConfigurationProperties('crank-shaft')
static class CrankShaft {
Optional<Double> rodLength = Optional.empty()
}
}
@alvaro_sanchez

31. Type-safe @ConfigurationProperties
#src/main/resources/application.yml
my:
engine:
manufacturer: Subaru
cylinders: 4
crank-shaft:
rodLength: 4
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32. Type-safe @ConfigurationProperties
— Simple injection:
@Singleton
class EngineImpl implements Engine {
final EngineConfig config
EngineImpl(EngineConfig config) {
this.config = config
}
}
@alvaro_sanchez

33. AOP

34. Micronaut's AOP
— Around Advice - decorates a method or class.
— Trace logging.
— Hystrix support.
— Cache abstraction.
— Circuit breaker pattern with retry support.
— Validation.
— Introduction Advice - introduces new behaviour to a class.
— HTTP client.
@alvaro_sanchez

35. Cache abstraction
@Singleton
@CacheConfig("pets")
class PetService {
@Cacheable
Pet findById(Long id) { ... }
@CachePut
void save(Pet pet) { ... }
@CacheInvalidate
void delete(Pet pet) { ... }
}
@alvaro_sanchez

36. HTTP Server

37. Hello World
//src/main/groovy/example/Application.groovy
package example
import io.micronaut.runtime.Micronaut
Micronaut.run(getClass())
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38. Hello World
//src/main/groovy/example/HelloController.groovy
@Controller("/")
class HelloController {
@Get("/hello/{name}")
String hello(String name) {
return "Hello $name!"
}
}
@alvaro_sanchez

39. Hello World
class HelloControllerSpec extends Specification {
@Shared @AutoCleanup EmbeddedServer embeddedServer =
ApplicationContext.run(EmbeddedServer)
@Shared @AutoCleanup HttpClient client =
HttpClient.create(embeddedServer.URL)
void "test hello world response"() {
expect:
client.toBlocking()
.retrieve(HttpRequest.GET('/hello/Greach')) == "Hello Greach!"
}
}
@alvaro_sanchez

40. JUnit with Java test
public class HelloWorldTest {
private static EmbeddedServer server;
private static HttpClient client;
@BeforeClass
public static void setupServer() {
server = ApplicationContext.run(EmbeddedServer.class);
client = server.getApplicationContext().createBean(HttpClient.class, server.getURL());
}
@AfterClass
public static void stopServer() {
if(server != null) { server.stop(); }
if(client != null) { client.stop(); }
}
@Test
public void testHelloWorkd() throws Exception {
String body = client.toBlocking().retrieve("/hello/Greach");
assertEquals(body, "Hello Greach!");
}
}
@alvaro_sanchez

41. Declarative routing
@Get("/hello")
String hello() {
return "Hello World"
}
@Get
String hello() {
return "Hello World"
}
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42. Programmatic routing
@Singleton
class MyRoutes extends GroovyRouteBuilder {
MyRoutes(ApplicationContext beanContext) { super(beanContext) }
@Inject
void bookResources(BookController bookController, AuthorController authorController) {
GET(bookController) {
POST("/hello{/message}", bookController.&hello)
}
GET(bookController, ID) {
GET(authorController)
}
}
}
@alvaro_sanchez

43. Request binding
— Body: String hello(@Body String body)
— Cookies: String hello(@CookieValue String myCookie)
— Headers: String hello(@Header String contentType)
— Parameters: String hello(@Parameter String myParam)
— Special cases:
— String hello(@Header Optional<String> contentType)
— String hello(@Parameter ZonedDateTime date)
@alvaro_sanchez

44. Direct request/response
manipulation
@Get("/hello")
HttpResponse<String> hello(HttpRequest<?> request) {
String name = request.getParameters()
.getFirst("name")
.orElse("Nobody");
return HttpResponse.ok("Hello " + name + "!!")
.header("X-My-Header", "Foo");
}
@alvaro_sanchez

45. Reactive request processing
@Post(consumes = MediaType.TEXT_PLAIN)
Single<MutableHttpResponse<String>> echoFlow(@Body Flowable<String> text) {
return text.collect(StringBuffer::new, StringBuffer::append)
.map(buffer ->
HttpResponse.ok(buffer.toString())
);
}
@alvaro_sanchez

46. Reactive responses
— Any type that implements the
org.reactivestreams.Publisher:
Flowable<String> hello() {}
— A Java's CompletableFuture instance:
CompletableFuture<String> hello() {}
— An io.micronaut.http.HttpResponse and optional
response body:
HttpResponse<Flowable<String>> hello() {}
@alvaro_sanchez

47. Non-reactive responses
— Any implementation of CharSequence:
String hello()
— Any simple POJO type
Book show()
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48. Threading model
The response type determines the thread pool used to
execute the request:
— Non-blocking requests will be executed in the Netty
event loop thread pool.
— Blocking requests will be executed on the I/O thread
pool.
@alvaro_sanchez

49. Reactive JSON parsing with
Jackson
@Post
public Single<HttpResponse<Person>> save(@Body Single<Person> person) {
return person.map(p -> {
//do something blocking, and then:
return HttpResponse.created(p);
}
);
}
@alvaro_sanchez

50. Non-reactive JSON parsing
If your method does not do any blocking I/O:
@Post
public HttpResponse<Person> save(@Body Person person) {
//do something, and then:
return HttpResponse.created(person);
}
@alvaro_sanchez

51. HTTP Client

52. Basics
//src/main/groovy/example/HelloController.groovy
@Controller("/")
class HelloController {
@Get("/hello/{name}") String hello(String name) { return "Hello $name!" }
}
//src/test/groovy/example/HelloClient.groovy
@Client('/')
interface HelloClient {
@Get("/hello/{name}") String hello(String name)
}
@alvaro_sanchez

53. Testing it
class HelloControllerSpec extends Specification {
@Shared @AutoCleanup EmbeddedServer embeddedServer =
ApplicationContext.run(EmbeddedServer)
void "test hello world"() {
given:
HelloClient client = embeddedServer.applicationContext.getBean(HelloClient)
expect:
client.hello("Fred") == "Hello Fred!"
}
}
@alvaro_sanchez

54. Features
— Service discovery aware: Consul and Eureka support.
— Load balancing: round robin, Netflix's Ribbon.
— Reactive: based on the return types.
— Fault tolerant: retry, fallback, circuit breaker.
@alvaro_sanchez

55. Fallback support
@Validated
interface PetOperations<T extends Pet> {
@Get("/") Single<List<T>> list()
}
@Client(id = "pets", path = "/v1/pets")
interface PetClient extends PetOperations<Pet> {
@Get("/") Single<List<Pet>> findAll()
}
@Fallback
class PetClientFallback implements PetOperations<Pet> {
Single<List<Pet>> list() { Single.just([] as List<Pet>) }
}
@alvaro_sanchez

56. Retry / circuit breaker support
@Client("/dodgy-api")
@Retryable(attempts = '5', delay = '5ms')
interface ApiClient { ... }
@Singleton
@CircuitBreaker(attempts = '5', delay = '5ms', reset = '300ms')
class MyService { ... }
@alvaro_sanchez

57. Retryable beans
@Singleton
class Neo4jDriverBuilder {
@Retryable(ServiceUnavailableException)
Driver buildDriver() {
//build driver
}
}
@alvaro_sanchez

58. Serverless

59. Simple functions as Groovy scripts
@Field @Inject Twitter twitterClient
@CompileStatic
UpdateResult updateStatus(Message status) {
Status s = twitterClient.updateStatus(status.text)
URL url= new URL("https://twitter.com/$s.user.screenName/status/${s.id}")
return new UpdateResult(url, s.createdAt.time)
}
@alvaro_sanchez

60. Function beans
import java.util.function.Function
@FunctionBean('book')
class BookFunction implements Function<Book, Book> {
@Override
Book apply(Book book) {
book.title = book.title.toUpperCase()
return book
}
}
@alvaro_sanchez

61. Function clients
@FunctionClient
interface TweetClient {
Single<Result> updateStatus(String text)
static class Result {
URL url
}
}
@alvaro_sanchez

62. Testing: directly
void "run function directly"() {
expect:
new HelloWorldFunction()
.hello(new Person(name: "Fred"))
.text == "Hello Fred!"
}
@alvaro_sanchez

63. Testing: REST
void "run function as REST service"() {
given:
EmbeddedServer server = ApplicationContext.run(EmbeddedServer)
HelloClient client = server.getApplicationContext().getBean(HelloClient)
when:
Message message = client.hello("Fred").blockingGet()
then:
message.text == "Hello Fred!"
}
@alvaro_sanchez

64. Testing: AWS Lambda
void "run execute function as lambda"() {
given:
ApplicationContext applicationContext = ApplicationContext.run(
'aws.lambda.functions.hello.functionName':'hello-world',
'aws.lambda.region':'us-east-1'
)
HelloClient client = applicationContext.getBean(HelloClient)
when:
Message message = client.hello("Fred").blockingGet()
then:
message.text == "Hello Fred!"
}
@alvaro_sanchez

65. Micronaut
Petstore

66. Petstore architecture
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67. Q & A
Álvaro Sánchez-Mariscal
@alvaro_sanchez