#113 Event Driven Architecture

Adds various changes including :
- Fixes to Javadoc
- Test refactoring and improvements
- Refactored EventDispatcher to be immutable
- Removed DynamicRouter interface since it not needed
- Renamed Channel to a more appropriate name - Handler

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

@@ -3,6 +3,7 @@ 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;
@@ -19,7 +20,7 @@ import com.iluwatar.eda.model.User;
 public class App {
 
   /**
-   * Once the {@link EventDispatcher} is initialised, channels related to specific events have to be
+   * 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.
@@ -34,8 +35,8 @@ public class App {
     dispatcher.registerChannel(UserUpdatedEvent.class, new UserUpdatedEventHandler());
 
     User user = new User("iluwatar");
-    dispatcher.dispatch(new UserCreatedEvent(user));
-    dispatcher.dispatch(new UserUpdatedEvent(user));
+    dispatcher.onEvent(new UserCreatedEvent(user));
+    dispatcher.onEvent(new UserUpdatedEvent(user));
   }
 
 }

event-driven-architecture/src/main/java/com/iluwatar/eda/EventDispatcher.java

@@ -1,50 +0,0 @@
-package com.iluwatar.eda;
-
-import com.iluwatar.eda.event.Event;
-import com.iluwatar.eda.framework.Channel;
-import com.iluwatar.eda.framework.DynamicRouter;
-
-import java.util.HashMap;
-import java.util.Map;
-
-/**
- * Handles the routing of {@link Event} messages to associated channels.
- * A {@link HashMap} is used to store the association between events and their respective handlers.
- *
- */
-public class EventDispatcher implements DynamicRouter<Event> {
-
-  private Map<Class<? extends Event>, Channel<?>> handlers;
-
-  public EventDispatcher() {
-    handlers = new HashMap<>();
-  }
-
-  /**
-   * Links an {@link Event} to a specific {@link Channel}.
-   *
-   * @param contentType The {@link Event} to be registered
-   * @param channel     The {@link Channel} that will be handling the {@link Event}
-   */
-  public void registerChannel(Class<? extends Event> contentType,
-                              Channel<?> channel) {
-    handlers.put(contentType, channel);
-  }
-
-  /**
-   * Dispatches an {@link Event} depending on it's type.
-   *
-   * @param content The {@link Event} to be dispatched
-   */
-  public void dispatch(Event content) {
-    handlers.get(content.getClass()).dispatch(content);
-  }
-
-  /**
-   * Returns a map of registered event handlers.
-   * @return {@link Map} of registered event handlers.
-   */
-  public Map<Class<? extends Event>, Channel<?>> getHandlers() {
-    return handlers;
-  }
-}

event-driven-architecture/src/main/java/com/iluwatar/eda/event/Event.java

@@ -1,5 +1,6 @@
 package com.iluwatar.eda.event;
 
+import com.iluwatar.eda.framework.EventDispatcher;
 import com.iluwatar.eda.framework.Message;
 
 /**
@@ -15,8 +16,8 @@ public class Event implements Message {
 
   /**
    * Returns the event type as a {@link Class} object
-   * In this example, this method is used by the {@link com.iluwatar.eda.EventDispatcher} to
-   * dispatch events depending on their type.
+   * In this example, this method is used by the {@link EventDispatcher} to
+   * onEvent events depending on their type.
    *
    * @return the Event type as a {@link Class}.
    */

event-driven-architecture/src/main/java/com/iluwatar/eda/event/UserCreatedEvent.java

@@ -3,7 +3,7 @@ package com.iluwatar.eda.event;
 import com.iluwatar.eda.model.User;
 
 /**
- * The {@link UserCreatedEvent} class should should be dispatched whenever a user has been created.
+ * The {@link UserCreatedEvent} should should be dispatched whenever a user has been created.
  * This class can be extended to contain details about the user has been created. In this example,
  * the entire {@link User} object is passed on as data with the event.
  */

event-driven-architecture/src/main/java/com/iluwatar/eda/event/UserUpdatedEvent.java

@@ -3,7 +3,7 @@ package com.iluwatar.eda.event;
 import com.iluwatar.eda.model.User;
 
 /**
- * The {@link UserUpdatedEvent} class should should be dispatched whenever a user has been updated.
+ * The {@link UserUpdatedEvent} should should be dispatched whenever a user has been updated.
  * This class can be extended to contain details about the user has been updated. In this example,
  * the entire {@link User} object is passed on as data with the event.
  */

event-driven-architecture/src/main/java/com/iluwatar/eda/framework/Channel.java

@@ -1,11 +0,0 @@
-package com.iluwatar.eda.framework;
-
-import com.iluwatar.eda.event.Event;
-
-/**
- * Channels are delivery points for messages. Every {@link Channel} is responsible for a single type
- * of message
- */
-public interface Channel<E extends Message> {
-  void dispatch(Event message);
-}

event-driven-architecture/src/main/java/com/iluwatar/eda/framework/DynamicRouter.java

@@ -1,13 +0,0 @@
-package com.iluwatar.eda.framework;
-
-/**
- * A {@link DynamicRouter} is responsible for selecting the proper path of a {@link Message}
- * Messages can be associated to Channels through the registerChannel method and dispatched by
- * calling the dispatch method.
- */
-public interface DynamicRouter<E extends Message> {
-
-  void registerChannel(Class<? extends E> contentType, Channel<?> channel);
-
-  void dispatch(E content);
-}

event-driven-architecture/src/main/java/com/iluwatar/eda/framework/EventDispatcher.java

@@ -0,0 +1,42 @@
+package com.iluwatar.eda.framework;
+
+import com.iluwatar.eda.event.Event;
+import com.iluwatar.eda.framework.Handler;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Handles the routing of {@link Event} messages to associated handlers.
+ * A {@link HashMap} is used to store the association between events and their respective handlers.
+ *
+ */
+public class EventDispatcher {
+
+  private Map<Class<? extends Event>, Handler<?>> handlers;
+
+  public EventDispatcher() {
+    handlers = new HashMap<>();
+  }
+
+  /**
+   * Links an {@link Event} to a specific {@link Handler}.
+   *
+   * @param eventType The {@link Event} to be registered
+   * @param handler   The {@link Handler} that will be handling the {@link Event}
+   */
+  public void registerChannel(Class<? extends Event> eventType,
+                              Handler<?> handler) {
+    handlers.put(eventType, handler);
+  }
+
+  /**
+   * Dispatches an {@link Event} depending on it's type.
+   *
+   * @param event The {@link Event} to be dispatched
+   */
+  public void onEvent(Event event) {
+    handlers.get(event.getClass()).onEvent(event);
+  }
+
+}

event-driven-architecture/src/main/java/com/iluwatar/eda/framework/Handler.java

@@ -0,0 +1,18 @@
+package com.iluwatar.eda.framework;
+
+import com.iluwatar.eda.event.Event;
+
+/**
+ * This interface can be implemented to handle different types of messages.
+ * Every handler is responsible for a single of type message
+ */
+public interface Handler<E extends Message> {
+
+  /**
+   * The onEvent method should implement and handle behavior related to the event.
+   * This can be as simple as calling another service to handle the event on publishing the event on
+   * a queue to be consumed by other sub systems.
+   * @param event the {@link Event} object to be handled.
+   */
+  void onEvent(Event event);
+}

event-driven-architecture/src/main/java/com/iluwatar/eda/framework/Message.java

@@ -2,8 +2,14 @@ package com.iluwatar.eda.framework;
 
 /**
  * A {@link Message} is an object with a specific type that is associated
- * to a specific {@link Channel}.
+ * to a specific {@link Handler}.
  */
 public interface Message {
+
+  /**
+   * Returns the message type as a {@link Class} object. In this example the message type is
+   * used to handle events by their type.
+   * @return the message type as a {@link Class}.
+   */
   Class<? extends Message> getType();
 }

event-driven-architecture/src/main/java/com/iluwatar/eda/handler/UserCreatedEventHandler.java

@@ -2,16 +2,15 @@ package com.iluwatar.eda.handler;
 
 import com.iluwatar.eda.event.Event;
 import com.iluwatar.eda.event.UserCreatedEvent;
-import com.iluwatar.eda.framework.Channel;
-import com.iluwatar.eda.model.User;
+import com.iluwatar.eda.framework.Handler;
 
 /**
  * Handles the {@link UserCreatedEvent} message.
  */
-public class UserCreatedEventHandler implements Channel<UserCreatedEvent> {
+public class UserCreatedEventHandler implements Handler<UserCreatedEvent> {
 
   @Override
-  public void dispatch(Event message) {
+  public void onEvent(Event message) {
 
     UserCreatedEvent userCreatedEvent = (UserCreatedEvent) message;
     System.out.printf("User with %s has been Created!", userCreatedEvent.getUser().getUsername());

event-driven-architecture/src/main/java/com/iluwatar/eda/handler/UserUpdatedEventHandler.java

@@ -1,17 +1,16 @@
 package com.iluwatar.eda.handler;
 
 import com.iluwatar.eda.event.Event;
-import com.iluwatar.eda.event.UserCreatedEvent;
 import com.iluwatar.eda.event.UserUpdatedEvent;
-import com.iluwatar.eda.framework.Channel;
+import com.iluwatar.eda.framework.Handler;
 
 /**
  * Handles the {@link UserUpdatedEvent} message.
  */
-public class UserUpdatedEventHandler implements Channel<UserUpdatedEvent> {
+public class UserUpdatedEventHandler implements Handler<UserUpdatedEvent> {
 
   @Override
-  public void dispatch(Event message) {
+  public void onEvent(Event message) {
 
     UserUpdatedEvent userUpdatedEvent = (UserUpdatedEvent) message;
     System.out.printf("User with %s has been Updated!", userUpdatedEvent.getUser().getUsername());