java-design-patterns/event-driven-architecture/src/main/java/com/iluwatar/eda/App.java

package com.iluwatar.eda;

import com.iluwatar.eda.event.Event;
import com.iluwatar.eda.event.UserCreatedEvent;
import com.iluwatar.eda.event.UserUpdatedEvent;
import com.iluwatar.eda.framework.EventDispatcher;
import com.iluwatar.eda.handler.UserCreatedEventHandler;
import com.iluwatar.eda.handler.UserUpdatedEventHandler;
import com.iluwatar.eda.model.User;

/**
 * An event-driven architecture (EDA) is a framework that orchestrates behavior around the
 * production, detection and consumption of events as well as the responses they evoke. An event is
 * any identifiable occurrence that has significance for system hardware or software. <p/> The
 * example below uses an {@link EventDispatcher} to link/register {@link Event} objects to their
 * respective handlers once an {@link Event} is dispatched, it's respective handler is invoked and
 * the {@link Event} is handled accordingly.
 *
 */
public class App {

  /**
   * Once the {@link EventDispatcher} is initialised, handlers related to specific events have to be
   * made known to the dispatcher by registering them. In this case the {@link UserCreatedEvent} is
   * bound to the UserCreatedEventHandler, whilst the {@link UserUpdatedEvent} is bound to the
   * {@link UserUpdatedEventHandler}. The dispatcher can now be called to dispatch specific events.
   * When a user is saved, the {@link UserCreatedEvent} can be dispatched.
   * On the other hand, when a user is updated, {@link UserUpdatedEvent} can be dispatched.
   *
   */
  public static void main(String[] args) {

    EventDispatcher dispatcher = new EventDispatcher();
    dispatcher.registerChannel(UserCreatedEvent.class, new UserCreatedEventHandler());
    dispatcher.registerChannel(UserUpdatedEvent.class, new UserUpdatedEventHandler());

    User user = new User("iluwatar");
    dispatcher.onEvent(new UserCreatedEvent(user));
    dispatcher.onEvent(new UserUpdatedEvent(user));
  }

}