#113 Event Driven Architecture

- added class diagram
- added more comments

event-driven-architecture/index.md

@@ -16,7 +16,7 @@ permalink: /patterns/event-driven-architecture
 
 **Real world examples:**
 
-* A Loan Application has been accepted/rejected (commercial business).
+* A Loan Application has been accepted/rejected (Commercial Business).
 * A new Rostering Schedule is ready for distribution to all crew (Airline Management System).
 * An Illegal Trade Pattern has been detected (Trading Fraud Detection System).
 * A simulated car has hits another simulated car (Commercial Racing Game).
@@ -28,4 +28,6 @@ permalink: /patterns/event-driven-architecture
 
 * [Event-driven architecture - Wikipedia](http://www.computerweekly.com/feature/Write-through-write-around-write-back-Cache-explained)
 * [Fundamental Components of an Event-Driven Architecture](http://giocc.com/fundamental-components-of-an-event-driven-architecture.html)
-* [Real World Applications/Event Driven Applications](https://wiki.haskell.org/Real_World_Applications/Event_Driven_Applications)
+* [Real World Applications/Event Driven Applications](https://wiki.haskell.org/Real_World_Applications/Event_Driven_Applications)
+* [Event-driven architecture definition](http://searchsoa.techtarget.com/definition/event-driven-architecture)
+*

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

@@ -0,0 +1,28 @@
+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.handler.UserCreatedEventHandler;
+import com.iluwatar.eda.handler.UserUpdatedEventHandler;
+
+/**
+ * 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 we 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 {
+
+    public static void main(String[] args) {
+        EventDispatcher dispatcher = new EventDispatcher();
+        dispatcher.registerChannel(UserCreatedEvent.class, new UserCreatedEventHandler());
+        dispatcher.registerChannel(UserUpdatedEvent.class, new UserUpdatedEventHandler());
+        dispatcher.dispatch(new UserCreatedEvent());
+        dispatcher.dispatch(new UserUpdatedEvent());
+    }
+
+}

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

@@ -0,0 +1,39 @@
+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;
+
+/**
+ * The {@link Event Dispatcher} handles 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<Class<? extends Event>, Channel>();
+    }
+
+    /**
+     * 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);
+    }
+
+    /**
+     * Dispathes 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);
+    }
+}

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

@@ -1,6 +1,6 @@
-package com.iluwatar.eda.advanced.events;
+package com.iluwatar.eda.event;
 
-import com.iluwatar.eda.advanced.framework.Message;
+import com.iluwatar.eda.framework.Message;
 
 public class Event implements Message {
     public Class<? extends Message> getType() {

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

@@ -0,0 +1,7 @@
+package com.iluwatar.eda.event;
+
+/**
+ * @author cfarrugia
+ */
+public class UserCreatedEvent extends Event {
+}

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

@@ -0,0 +1,4 @@
+package com.iluwatar.eda.event;
+
+public class UserUpdatedEvent extends Event {
+}

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

@@ -0,0 +1,9 @@
+package com.iluwatar.eda.framework;
+
+/**
+ * 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(E message);
+}

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

@@ -0,0 +1,11 @@
+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/Message.java

@@ -0,0 +1,9 @@
+package com.iluwatar.eda.framework;
+
+/**
+ * A {@link Message} is an object with a specific type that is associated to a
+ * specific {@link Channel}
+ */
+public interface Message {
+    Class<? extends Message> getType();
+}

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

@@ -1,10 +1,10 @@
-package com.iluwatar.eda.advanced.handler;
+package com.iluwatar.eda.handler;
 
-import com.iluwatar.eda.advanced.events.UserCreatedEvent;
-import com.iluwatar.eda.advanced.framework.Channel;
+import com.iluwatar.eda.event.UserCreatedEvent;
+import com.iluwatar.eda.framework.Channel;
 
 /**
- * @author cfarrugia
+ * Handles the {@link UserCreatedEvent} message
  */
 public class UserCreatedEventHandler implements Channel<UserCreatedEvent> {
 

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

@@ -1,8 +1,11 @@
-package com.iluwatar.eda.advanced.handler;
+package com.iluwatar.eda.handler;
 
-import com.iluwatar.eda.advanced.events.UserUpdatedEvent;
-import com.iluwatar.eda.advanced.framework.Channel;
+import com.iluwatar.eda.event.UserUpdatedEvent;
+import com.iluwatar.eda.framework.Channel;
 
+/**
+ * Handles the {@link UserUpdatedEvent} message
+ */
 public class UserUpdatedEventHandler implements Channel<UserUpdatedEvent> {
 
     public void dispatch(UserUpdatedEvent message) {