Lagom in Practice

LAGOM IN PRACTICE
THE NEW JAVA MICROSERVICES FRAMEWORK

ABOUT ME
Yannick De Turck
Java Developer
Scala and Play enthousiast
Ordina Belgium
@YannickDeTurck
https://github.com/YannickDeTurck

BLOGPOST LAGOM
Lagom: First Impressions and Initial Comparison to Spring Cloud
http://bit.ly/1sClupt

TOPICS
Introduction
Writing microservices
Demo: writing a simple service
ES & CQRS
Demo: Lagom Shop

MEET LAGOM
Lightbend's microservices framework
Focus on reactiveness
MVP version
Java API available, Scala API coming soon

DESIGN PHILOSOPHY
Opinionated
Message-Driven and Asynchronous
Streaming rst-class concept
Distributed persistent patterns using ES and CQRS
Embraces Domain-Driven Design

DEVELOPER PRODUCTIVITY
Hot code reloading
Start up with $ runAll
Intra-service communication is managed for you

ARCHITECTURE AND TECHNOLOGIES
Scala
Java
Play Framework
Akka Cluster & Akka Persistence
sbt
Cassandra
Guice
ConductR

PROJECT STRUCTURE
helloworld-api → Microservice API submodule
└ src/main/java → Java source code interfaces with model objects
helloworld-impl → Microservice implementation submodule
└ logs → Logs of the microservice
└ src/main/java → Java source code implementation of the API submodule
└ src/main/resources → Contains the microservice application config
└ src/test/java → Java source code unit tests
logs → Logs of the Lagom system
project → Sbt configuration files
└ build.properties → Marker for sbt project
└ plugins.sbt → Sbt plugins including the declaration for Lagom itself
.gitignore → Git ignore file
build.sbt → Application build script

API INTERFACE
public interface HelloService extends Service {
ServiceCall<NotUsed, String> hello(String name);
ServiceCall<GreetingMessage, String> useGreeting(String id);
@Override
default Descriptor descriptor() {
return named("helloservice").with(
restCall(Method.GET, "/api/hello/:name", this::hello),
restCall(Method.POST, "/api/hello/:id", this::useGreeting)
).withAutoAcl(true);
}
}

API IMPLEMENTATION
public class HelloServiceImpl implements HelloService {
List<String> savedGreetings = new ArrayList<>();
@Override
public ServiceCall<NotUsed, String> hello(String name) {
return (request) -> {
CompletableFuture.completedFuture("Hello, " + name);
};
}
@Override
public ServiceCall<GreetingMessage, String> useGreeting() {
String greeting = request.getGreeting();
savedGreeting.add(greeting);
CompletableFuture.completedFuture("Greeting '" + greeting + "' saved!");
};
}
}

API MODULE
public class HelloServiceModule extends AbstractModule
implements ServiceGuiceSupport {
@Override
protected void configure() {
bindServices(serviceBinding(HelloService.class, HelloServiceImpl.class));
bindClient(OtherService.class);
}
}

API MODULE
The module is de ned in the application.con g
play.modules.enabled += sample.helloworld.impl.HelloServiceModule

REGISTERING THE MICROSERVICE
build.sbt
lazy val helloworldApi = project("helloworld-api")
.settings(
version := "1.0-SNAPSHOT",
libraryDependencies += lagomJavadslApi
)
lazy val helloworldImpl = project("helloworld-impl")
.enablePlugins(LagomJava)
.settings(
version := "1.0-SNAPSHOT",
libraryDependencies ++= Seq(
lagomJavadslPersistence,
lagomJavadslTestKit
)
)
.settings(lagomForkedTestSettings: _*)
.dependsOn(helloworldApi)

TESTING THE MICROSERVICE
$ curl localhost:24266/api/hello/World
Hello, World!
$ curl -H "Content-Type: application/json" -X POST -d
'{"message": "Hello "}' http://localhost:24266/api/hello/World
Greeting 'Hello' was saved!

TESTING THE MICROSERVICE
public class HelloServiceTest {
private static ServiceTest.TestServer server;
@Test
public void shouldRespondHello() throws Exception {
withServer(defaultSetup(), server -> {
HelloService service = server.client(HelloService.class);
String hello = service.hello("Yannick")
.invoke(NotUsed.getInstance()).toCompletableFuture().get(5, SECONDS);
assertEquals("Hello, Yannick", hello);
});
}
}

DEMO: WRITING A SIMPLE SERVICE

DEMO
Implement a new service: capitalise
Write a unit test
Deploy it to ConductR

EVENT SOURCING
Capture all changes as domain events
Handlers process these events

EVENT SOURCING BENEFITS
All events are stored in an event store
No object-relational impedance mismatch
Built-in audit mechanism and historical tracing
Performance, simpli cation and scalability
Testability
Debugging by replaying the event log

CQRS
Separation of write- and read-side
Scalability
Di erent models for write- and read-side
Eventual consistency

CQRS AND ES INTRODUCTION
https://msdn.microsoft.com/en-us/library/jj591573.aspx

ES AND CQRS - PERSISTENTENTITY
public class HelloWorld extends PersistentEntity {
@Override
public Behavior initialBehavior(Optional snapshotState) {
BehaviorBuilder b = newBehaviorBuilder(
snapshotState.orElse(new WorldState("Hello", LocalDateTime.now().toString())));
b.setCommandHandler(UseGreetingMessage.class, (cmd, ctx) ->
ctx.thenPersist(new GreetingMessageChanged(cmd.message),
evt -> ctx.reply(Done.getInstance()))
);
b.setEventHandler(GreetingMessageChanged.class,
evt -> new WorldState(evt.message, LocalDateTime.now().toString()));
b.setReadOnlyCommandHandler(Hello.class,
(cmd, ctx) -> ctx.reply(state().message + ", " + cmd.name + "!")
);
}
}

ES AND CQRS - STATE
@Immutable
@JsonDeserialize
public final class WorldState implements CompressedJsonable {
public final String message;
public final String timestamp;
@JsonCreator
public WorldState(String message, String timestamp) {
this.message = Preconditions.checkNotNull(message, "message");
this.timestamp = Preconditions.checkNotNull(timestamp, "timestamp");
}
// equals, hashcode, toString, ...
}

ES AND CQRS - COMMAND
public interface HelloCommand extends Jsonable {
@Immutable
@JsonDeserialize
public final class UseGreetingMessage implements HelloCommand,
CompressedJsonable, PersistentEntity.ReplyType {
@JsonCreator
public UseGreetingMessage(String message) {
}
// equals, hashcode, toString,...
}
}

ES AND CQRS - EVENT
public interface HelloEvent extends Jsonable {
@Immutable
@JsonDeserialize
public final class GreetingMessageChanged implements HelloEvent {
@JsonCreator
public GreetingMessageChanged(String message) {
}
// equals, hashCode, toString
}

ES AND CQRS - SERVICEIMPL
@Override
public ServiceCall useGreeting(String id) {
PersistentEntityRef ref =
persistentEntityRegistry.refFor(HelloWorld.class, id);
return ref.ask(new UseGreetingMessage(request.message));
};
}

LAGOM SHOP
Item Service: Create and lookup items
Order Service: Create and lookup orders for items
Play front-end

QUESTIONS?
Lagom Shop & Presentation:
https://github.com/yannickdeturck/lagom-shop
Blogpost Lagom: First Impressions and Initial Comparison to Spring
Cloud http://bit.ly/1sClupt
Podcast Lightbend Podcast Ep. 09: Andreas Evers test drives Lagom
in comparison with Spring Cloud: http://bit.ly/25XVT8w

Lagom in Practice

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