Added event aggregator pattern.

event-aggregator/etc/classes.ucls

@@ -0,0 +1,124 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
+  <class id="1" language="java" name="com.iluwatar.KingsHand" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/KingsHand.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="805" y="431"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <interface id="2" language="java" name="com.iluwatar.EventObserver" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/EventObserver.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="784" y="586"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <enumeration id="3" language="java" name="com.iluwatar.Weekday" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/Weekday.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="437" y="195"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </enumeration>  
+  <class id="4" language="java" name="com.iluwatar.KingJoffrey" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/KingJoffrey.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="380" y="413"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="5" language="java" name="com.iluwatar.LordVarys" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/LordVarys.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="581" y="422"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="6" language="java" name="com.iluwatar.LordBaelish" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/LordBaelish.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1050" y="422"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="7" language="java" name="com.iluwatar.EventEmitter" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/EventEmitter.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1036" y="149"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="8" language="java" name="com.iluwatar.Scout" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/Scout.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1275" y="422"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <enumeration id="9" language="java" name="com.iluwatar.Event" project="event-aggregator" 
+    file="/event-aggregator/src/main/java/com/iluwatar/Event.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="721" y="159"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </enumeration>  
+  <realization id="10">    
+    <end type="SOURCE" refId="1"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <association id="11">    
+    <bendpoint x="927" y="360"/>    
+    <end type="SOURCE" refId="7" navigable="false">      
+      <attribute id="12" name="observers"/>      
+      <multiplicity id="13" minimum="0" maximum="2147483647"/>    
+    </end>    
+    <end type="TARGET" refId="2" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <generalization id="14">    
+    <end type="SOURCE" refId="1"/>    
+    <end type="TARGET" refId="7"/>  
+  </generalization>  
+  <generalization id="15">    
+    <end type="SOURCE" refId="6"/>    
+    <end type="TARGET" refId="7"/>  
+  </generalization>  
+  <realization id="16">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <generalization id="17">    
+    <end type="SOURCE" refId="8"/>    
+    <end type="TARGET" refId="7"/>  
+  </generalization>  
+  <generalization id="18">    
+    <end type="SOURCE" refId="5"/>    
+    <end type="TARGET" refId="7"/>  
+  </generalization>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

event-aggregator/pom.xml

@@ -0,0 +1,17 @@
+<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>
+	<parent>
+		<groupId>com.iluwatar</groupId>
+		<artifactId>java-design-patterns</artifactId>
+		<version>1.0-SNAPSHOT</version>
+	</parent>
+	<artifactId>event-aggregator</artifactId>
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+</project>

event-aggregator/src/main/java/com/iluwatar/App.java

@@ -0,0 +1,35 @@
+package com.iluwatar;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 
+ * The Event Aggregator pattern channels events from multiple objects 
+ * into a single object to simplify registration for clients.
+ * 
+ * In the example LordBaelish, LordVarys and Scout deliver events to
+ * KingsHand. KingsHand, the event aggregator, then delivers the events
+ * to KingJoffrey.
+ *
+ */
+public class App {
+
+	public static void main(String[] args) {
+		
+		KingJoffrey kingJoffrey = new KingJoffrey();
+		KingsHand kingsHand = new KingsHand(kingJoffrey);
+
+		List<EventEmitter> emitters = new ArrayList<>();
+		emitters.add(kingsHand);
+		emitters.add(new LordBaelish(kingsHand));
+		emitters.add(new LordVarys(kingsHand));
+		emitters.add(new Scout(kingsHand));
+		
+		for (Weekday day: Weekday.values()) {
+			for (EventEmitter emitter: emitters) {
+				emitter.timePasses(day);
+			}
+		}
+	}
+}

event-aggregator/src/main/java/com/iluwatar/Event.java

@@ -0,0 +1,21 @@
+package com.iluwatar;
+
+/**
+ * 
+ * Event enumeration.
+ *
+ */
+public enum Event {
+
+	STARK_SIGHTED("Stark sighted"), WARSHIPS_APPROACHING("Warships approaching"), TRAITOR_DETECTED("Traitor detected");
+	
+	private String description;
+	
+	Event(String description) {
+		this.description = description;	
+	}
+	
+    public String toString() {
+        return description;
+    }
+}

event-aggregator/src/main/java/com/iluwatar/EventEmitter.java

@@ -0,0 +1,35 @@
+package com.iluwatar;
+
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * 
+ * EventEmitter is the base class for event producers that can be observed.
+ *
+ */
+public abstract class EventEmitter {
+
+	private List<EventObserver> observers;
+
+	public EventEmitter() {
+		observers = new LinkedList<>();
+	}
+
+	public EventEmitter(EventObserver obs) {
+		this();
+		registerObserver(obs);
+	}
+	
+	public void registerObserver(EventObserver obs) {
+		observers.add(obs);
+	}
+	
+	protected void notifyObservers(Event e) {
+		for (EventObserver obs: observers) {
+			obs.onEvent(e);
+		}
+	}
+	
+	public abstract void timePasses(Weekday day);
+}

event-aggregator/src/main/java/com/iluwatar/EventObserver.java

@@ -0,0 +1,12 @@
+package com.iluwatar;
+
+/**
+ * 
+ * Observers of events implement this interface.
+ *
+ */
+public interface EventObserver {
+	
+	void onEvent(Event e);
+
+}

event-aggregator/src/main/java/com/iluwatar/KingJoffrey.java

@@ -0,0 +1,14 @@
+package com.iluwatar;
+
+/**
+ * 
+ * KingJoffrey observes events from KingsHand.
+ *
+ */
+public class KingJoffrey implements EventObserver {
+
+	@Override
+	public void onEvent(Event e) {
+		System.out.println("Received event from the King's Hand: " + e.toString());
+	}
+}

event-aggregator/src/main/java/com/iluwatar/KingsHand.java

@@ -0,0 +1,28 @@
+package com.iluwatar;
+
+/**
+ * 
+ * KingsHand observes events from multiple sources and delivers them
+ * to listeners.
+ *
+ */
+public class KingsHand extends EventEmitter implements EventObserver {
+
+	public KingsHand() {
+		super();
+	}
+
+	public KingsHand(EventObserver obs) {
+		super(obs);
+	}
+	
+	@Override
+	public void onEvent(Event e) {
+		notifyObservers(e);
+	}
+
+	@Override
+	public void timePasses(Weekday day) {
+		// NOP
+	}
+}

event-aggregator/src/main/java/com/iluwatar/LordBaelish.java

@@ -0,0 +1,24 @@
+package com.iluwatar;
+
+/**
+ * 
+ * LordBaelish produces events.
+ *
+ */
+public class LordBaelish extends EventEmitter {
+	
+	public LordBaelish() {
+		super();
+	}
+
+	public LordBaelish(EventObserver obs) {
+		super(obs);
+	}
+	
+	@Override
+	public void timePasses(Weekday day) {
+		if (day.equals(Weekday.FRIDAY)) {
+			notifyObservers(Event.STARK_SIGHTED);
+		}
+	}
+}

event-aggregator/src/main/java/com/iluwatar/LordVarys.java

@@ -0,0 +1,24 @@
+package com.iluwatar;
+
+/**
+ * 
+ * LordVarys produces events.
+ *
+ */
+public class LordVarys extends EventEmitter {
+	
+	public LordVarys() {
+		super();
+	}
+
+	public LordVarys(EventObserver obs) {
+		super(obs);
+	}
+	
+	@Override
+	public void timePasses(Weekday day) {
+		if (day.equals(Weekday.SATURDAY)) {
+			notifyObservers(Event.TRAITOR_DETECTED);
+		}
+	}
+}

event-aggregator/src/main/java/com/iluwatar/Scout.java

@@ -0,0 +1,24 @@
+package com.iluwatar;
+
+/**
+ * 
+ * Scout produces events.
+ *
+ */
+public class Scout extends EventEmitter {
+	
+	public Scout() {
+		super();
+	}
+
+	public Scout(EventObserver obs) {
+		super(obs);
+	}
+	
+	@Override
+	public void timePasses(Weekday day) {
+		if (day.equals(Weekday.TUESDAY)) {
+			notifyObservers(Event.WARSHIPS_APPROACHING);
+		}
+	}
+}

event-aggregator/src/main/java/com/iluwatar/Weekday.java

@@ -0,0 +1,16 @@
+package com.iluwatar;
+
+public enum Weekday {
+	
+	MONDAY("Monday"), TUESDAY("Tuesday"), WEDNESDAY("Wednesday"), THURSDAY("Thursday"), FRIDAY("Friday"), SATURDAY("Saturday"), SUNDAY("Sunday");
+
+	private String description;
+	
+	Weekday(String description) {
+		this.description = description;
+	}
+	
+	public String toString() {
+		return description;
+	}
+}

event-aggregator/src/test/java/com/iluwatar/AppTest.java

@@ -0,0 +1,13 @@
+package com.iluwatar;
+import org.junit.Test;
+
+import com.iluwatar.App;
+
+public class AppTest {
+
+	@Test
+	public void test() {
+		String[] args = {};
+		App.main(args);
+	}
+}

pom.xml

@@ -38,7 +38,8 @@
 		<module>double-checked-locking</module>
 		<module>servant</module>
 		<module>service-locator</module>
-    <module>null-object</module>
+	    <module>null-object</module>
+	    <module>event-aggregator</module>
   </modules>
 
 	<dependencyManagement>