Overview

Simple event handling library!

This project composes of components for implementing the event handling parts of the DDD/CQRS pattern. This library was built with simplicity, modularity and pluggability in mind.

Features

Send events to one or many registered event handlers.
Multiple ways of registering event handlers:
- Simple registration (no IoC container).
- IoC container registration
  - achieved by creating implementations of EventHandlerProvider:
    - Spring Context
    - Guice
- Attribute registration (Soon!)
  - achieved by marking methods with @EventHandler annotations.

Installation

You can simply clone this repository, build the source, reference the jar from your project, and code away!
XerJ.EventStack is also available in the Maven Central:

Getting Started

Sample Command and Command Handler

// Example command.
public class ProductRegisteredEvent
{
    private final int productId;
    private final String productName;

    public ProductRegisteredEvent(int productId, String productName) 
    {
        this.productId = productId;
        this.productName = productName;
    }

    public int getProductId() {
        return productId;
    }

    public String getProductName() {
        return productName;
    }
}

// Event handler 1.
public class ProductRegisteredNotificationHandler : EventHandler<ProductRegisteredEvent>
{
    private final NotificationService notificationService;

    public ProductRegisteredNotificationHandler(NotificationService notificationService)
    {
        this.notificationService = notificationService;
    }

    @Override
    public CompletableFuture<Void> handle(ProductRegisteredEvent event)
    {
        return notificationService.notify("Product registered! - " + event.getProductName());
    }
}

... Other event handlers

Event Handler Registration

Before we can dispatch any events, first we need to register our event handlers. There are several ways to do this:

1. Simple Registration (No IoC container)

public static void main(String[] args)
{
    RegistryEventHandlerProvider provider = new RegistryEventHandlerProvider(registry -> {
        registry.registerEventHandler(ProductRegisteredEvent.class, () -> new ProductRegisteredNotificationHandler(
            new EmailNotificationService()
        ));
    });

    EventDispatcher dispatcher = new EventDispatcher(provider);
    
    // Dispatch event.
    CompletableFuture<Void> future = dispatcher.send(new ProductRegisteredEvent(1, "My Product Name"));
}

2. Container Registration

Spring Context

public static void main(String[] args)
{ 
    ApplicationContext appContext = new AnnotationConfigApplicationContext(BeanConfigs.class);

    SpringContextEventHandlerPovider provider = new SpringContextEventHandlerPovider(appContext);

    EventDispatcher dispatcher = new EventDispatcher(provider);

    // Dispatch event.
    CompletableFuture<Void> future = dispatcher.send(new ProductRegisteredEvent(1, "My Product Name"));
}

Guice

public static void main(String[] args)
{ 
    Injector injector = Guice.createInjector(new AppModule());

    GuiceEventHandlerPovider provider = new GuiceEventHandlerPovider(injector);

    EventDispatcher dispatcher = new EventDispatcher(provider);

    // Dispatch event.
    CompletableFuture<Void> future = dispatcher.send(new ProductRegisteredEvent(1, "My Product Name"));
}

joel-jeremy/xerj.eventstack

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