AxonFramework - initial exploration

For the record, this demo is kind of copied from the quickstart but it is in some ways more elaborate and using the latest and greatest version 2.0.7

	<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.pelssers</groupId>
	<artifactId>axondemo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<properties>
	<spring.version>3.1.2.RELEASE</spring.version>
	<axon.version>2.0.7</axon.version>
	<junit.version>4.11</junit.version>
	</properties>
	<dependencies>
	<dependency>
	<groupId>org.axonframework</groupId>
	<artifactId>axon-core</artifactId>
	<version>${axon.version}</version>
	<scope>compile</scope>
	</dependency>
	<dependency>
	<groupId>org.axonframework</groupId>
	<artifactId>axon-test</artifactId>
	<version>${axon.version}</version>
	<scope>test</scope>
	</dependency>
	<dependency>
	<groupId>org.springframework</groupId>
	<artifactId>spring-context</artifactId>
	<version>${spring.version}</version>
	<scope>compile</scope>
	</dependency>
	<dependency>
	<groupId>junit</groupId>
	<artifactId>junit</artifactId>
	<version>${junit.version}</version>
	<scope>test</scope>
	</dependency>
	</dependencies>
	</project>

view raw gistfile1.xml hosted with ❤ by GitHub

Now we start thinking about the behaviour of our little demo application. A user can create a new todo item and he can mark an existing item as completed.

	package nl.pelssers.axondemo.api;
	import org.axonframework.commandhandling.annotation.TargetAggregateIdentifier;
	public class CreateToDoItemCommand {
	@TargetAggregateIdentifier
	private final String todoId;
	private final String description;
	public CreateToDoItemCommand(String todoId, String description) {
	this.todoId = todoId;
	this.description = description;
	}
	public String getTodoId() {
	return todoId;
	}
	public String getDescription() {
	return description;
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

	package nl.pelssers.axondemo.api;
	import org.axonframework.commandhandling.annotation.TargetAggregateIdentifier;
	public class MarkCompletedCommand {
	@TargetAggregateIdentifier
	private String todoId;
	public MarkCompletedCommand(String todoId) {
	this.todoId = todoId;
	}
	public String getTodoId() {
	return todoId;
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

When commands are issued, something is bound to happen, so we also need to think about what events occur.

	package nl.pelssers.axondemo.api;
	public class ToDoItemCreatedEvent {
	private final String todoId;
	private final String description;
	public ToDoItemCreatedEvent(String todoId, String description) {
	this.todoId = todoId;
	this.description = description;
	}
	public String getTodoId() {
	return todoId;
	}
	public String getDescription() {
	return description;
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

	package nl.pelssers.axondemo.api;
	public class ToDoItemCompletedEvent {
	private final String todoId;
	public ToDoItemCompletedEvent(String todoId) {
	this.todoId = todoId;
	}
	public String getTodoId() {
	return todoId;
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

We also need to think about our aggregate, in this case our ToDoItem

	package nl.pelssers.axondemo.api;
	import org.axonframework.commandhandling.annotation.CommandHandler;
	import org.axonframework.eventhandling.annotation.EventHandler;
	import org.axonframework.eventsourcing.annotation.AbstractAnnotatedAggregateRoot;
	import org.axonframework.eventsourcing.annotation.AggregateIdentifier;
	public class ToDoItem extends AbstractAnnotatedAggregateRoot<ToDoItem>{
	private static final long serialVersionUID = 5438310735257852739L;
	@AggregateIdentifier
	private String id;
	public ToDoItem() {
	}
	/**
	* This is a constructor annotated with a CommandHandler. It makes sense that a ToDoItem
	* instance gets created whenever a CreateToDoItemCommand is issued. The command handler
	* creates a ToDoItemCreatedEvent which gets registered with the EventContainer by calling apply
	* @param command
	*/
	@CommandHandler
	public ToDoItem(CreateToDoItemCommand command) {
	apply(new ToDoItemCreatedEvent(command.getTodoId(), command.getDescription()));
	}
	@EventHandler
	public void on(ToDoItemCreatedEvent event) {
	this.id = event.getTodoId();
	}
	@CommandHandler
	public void markCompleted(MarkCompletedCommand command) {
	apply(new ToDoItemCompletedEvent(id));
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

Of course we need to test if events are properly created when a command is issued.

	package nl.pelssers.axondemo;
	import nl.pelssers.axondemo.api.CreateToDoItemCommand;
	import nl.pelssers.axondemo.api.MarkCompletedCommand;
	import nl.pelssers.axondemo.api.ToDoItem;
	import nl.pelssers.axondemo.api.ToDoItemCompletedEvent;
	import nl.pelssers.axondemo.api.ToDoItemCreatedEvent;
	import org.axonframework.test.FixtureConfiguration;
	import org.axonframework.test.Fixtures;
	import org.junit.Before;
	import org.junit.Test;
	public class ToDoItemTest {
	private FixtureConfiguration<ToDoItem> fixture;
	private final static String ITEM1_ID = "TODO-1";
	private final static String ITEM1_DESCRIPTION = "Clean house";
	@Before
	public void setUp() throws Exception {
	fixture = Fixtures.newGivenWhenThenFixture(ToDoItem.class);
	}
	@Test
	public void testCreateToDoItem() throws Exception {
	fixture
	.given()
	.when(new CreateToDoItemCommand(ITEM1_ID, ITEM1_DESCRIPTION))
	.expectEvents(new ToDoItemCreatedEvent(ITEM1_ID, ITEM1_DESCRIPTION));
	}
	@Test
	public void testMarkToDoItemAsCompleted() throws Exception {
	fixture
	.given(new ToDoItemCreatedEvent(ITEM1_ID, ITEM1_DESCRIPTION))
	.when(new MarkCompletedCommand(ITEM1_ID))
	.expectEvents(new ToDoItemCompletedEvent(ITEM1_ID));
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

We also need to configure the application, as usual we will use Spring to wire our app.

	package nl.pelssers.axondemo.configuration;
	import java.io.File;
	import nl.pelssers.axondemo.ToDoEventHandler;
	import nl.pelssers.axondemo.api.ToDoItem;
	import org.axonframework.commandhandling.CommandBus;
	import org.axonframework.commandhandling.SimpleCommandBus;
	import org.axonframework.commandhandling.annotation.AggregateAnnotationCommandHandler;
	import org.axonframework.commandhandling.gateway.CommandGateway;
	import org.axonframework.commandhandling.gateway.DefaultCommandGateway;
	import org.axonframework.eventhandling.EventBus;
	import org.axonframework.eventhandling.SimpleEventBus;
	import org.axonframework.eventhandling.annotation.AnnotationEventListenerAdapter;
	import org.axonframework.eventsourcing.EventSourcingRepository;
	import org.axonframework.eventstore.EventStore;
	import org.axonframework.eventstore.fs.FileSystemEventStore;
	import org.axonframework.eventstore.fs.SimpleEventFileResolver;
	import org.springframework.context.annotation.Bean;
	import org.springframework.context.annotation.Configuration;
	@Configuration
	public class AxonDemoConfiguration {
	@Bean
	public CommandBus commandBus() {
	return new SimpleCommandBus();
	}
	@Bean
	public CommandGateway commandGateway() {
	return new DefaultCommandGateway(commandBus());
	}
	@Bean
	public EventStore eventStore() {
	return new FileSystemEventStore(new SimpleEventFileResolver(new File("c:/tmp/axondemo")));
	}
	@Bean
	public EventBus eventBus() {
	return new SimpleEventBus();
	}
	@Bean
	public EventSourcingRepository<ToDoItem> todoRepository() {
	EventSourcingRepository<ToDoItem> repository = new EventSourcingRepository<ToDoItem>(ToDoItem.class, eventStore());
	repository.setEventBus(eventBus());
	return repository;
	}
	@SuppressWarnings("unchecked")
	@Bean
	public AggregateAnnotationCommandHandler<ToDoItem> toDoItemHandler() {
	return AggregateAnnotationCommandHandler.subscribe(ToDoItem.class, todoRepository(), commandBus());
	}
	@Bean
	public AnnotationEventListenerAdapter todoEventHandler() {
	return AnnotationEventListenerAdapter.subscribe(new ToDoEventHandler(), eventBus());
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

The demo app just issues 2 commands, mimicking what a user might do. And to make it interesting we also create an event handler for our ToDoItem events.

	package nl.pelssers.axondemo;
	import nl.pelssers.axondemo.api.CreateToDoItemCommand;
	import nl.pelssers.axondemo.api.MarkCompletedCommand;
	import nl.pelssers.axondemo.configuration.AxonDemoConfiguration;
	import org.axonframework.commandhandling.gateway.CommandGateway;
	import org.springframework.context.ApplicationContext;
	import org.springframework.context.annotation.AnnotationConfigApplicationContext;
	import org.springframework.stereotype.Component;
	@Component
	public class ToDoApplication {
	private CommandGateway commandGateway;
	public ToDoApplication(CommandGateway commandGateway) {
	this.commandGateway = commandGateway;
	}
	/**
	* @param args
	*/
	public static void main(String[] args) {
	ApplicationContext context = new AnnotationConfigApplicationContext(AxonDemoConfiguration.class);
	ToDoApplication todoApplication = new ToDoApplication(context.getBean(CommandGateway.class));
	todoApplication.run();
	}
	private void run() {
	final String itemId = "TODO-1";
	commandGateway.send(new CreateToDoItemCommand(itemId, "Clean house"));
	commandGateway.send(new MarkCompletedCommand(itemId));
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

	package nl.pelssers.axondemo;
	import org.axonframework.eventhandling.annotation.EventHandler;
	import nl.pelssers.axondemo.api.ToDoItemCompletedEvent;
	import nl.pelssers.axondemo.api.ToDoItemCreatedEvent;
	public class ToDoEventHandler {
	@EventHandler
	public void handle(ToDoItemCreatedEvent event) {
	System.out.println("We've got something to do: " + event.getDescription() + " (" + event.getTodoId() + ")");
	}
	@EventHandler
	public void handle(ToDoItemCompletedEvent event) {
	System.out.println("We've completed a task: " + event.getTodoId());
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

When we run the ToDoApplication we notice a file gets created in c:/tmp/axondemo/ for our aggregate called TODO-1.events. Also we nicely see some output appearing in the console:

We've got something to do: Clean house (TODO-1)
We've completed a task: TODO-1