Merge pull request iluwatar#227 from iluwatar/message-channel

iluwatar · iluwatar · commit e33d037c0fac · 2015-09-02T23:06:22.000+03:00
Message Channel EIP
diff --git a/message-channel/.gitignore b/message-channel/.gitignore
@@ -0,0 +1 @@
+/target/
diff --git a/message-channel/etc/message-channel.png b/message-channel/etc/message-channel.png
diff --git a/message-channel/etc/message-channel.ucls b/message-channel/etc/message-channel.ucls
diff --git a/message-channel/index.md b/message-channel/index.md
@@ -0,0 +1,21 @@
+---
+layout: pattern
+title: Message Channel
+folder: message-channel
+permalink: /patterns/message-channel/
+categories: Integration
+tags: Java
+---
+
+**Intent:** When two applications communicate using a messaging system they do it by using logical addresses
+of the system, so called Message Channels.
+
+![alt text](./etc/message-channel.png "Message Channel")
+
+**Applicability:** Use the Message Channel pattern when
+
+* two or more applications need to communicate using a messaging system
+
+**Real world examples:**
+
+* [akka-camel](http://doc.akka.io/docs/akka/snapshot/scala/camel.html)
diff --git a/message-channel/pom.xml b/message-channel/pom.xml
@@ -0,0 +1,27 @@
+<?xml version="1.0"?>
+<project
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
+	xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>com.iluwatar</groupId>
+		<artifactId>java-design-patterns</artifactId>
+		<version>1.6.0</version>
+	</parent>
+	<artifactId>message-channel</artifactId>
+	<dependencies>
+		<dependency>
+			<groupId>org.apache.camel</groupId>
+			<artifactId>camel-core</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.camel</groupId>
+			<artifactId>camel-stream</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+</project>
diff --git a/message-channel/src/main/java/com/iluwatar/message/channel/App.java b/message-channel/src/main/java/com/iluwatar/message/channel/App.java
@@ -0,0 +1,53 @@
+package com.iluwatar.message.channel;
+
+import org.apache.camel.CamelContext;
+import org.apache.camel.builder.RouteBuilder;
+import org.apache.camel.impl.DefaultCamelContext;
+
+/**
+ * 
+ * When two applications communicate with each other using a messaging system
+ * they first need to establish a communication channel that will carry the
+ * data. Message Channel decouples Message producers and consumers.
+ * <p>
+ * The sending application doesn't necessarily know what particular application
+ * will end up retrieving it, but it can be assured that the application that
+ * retrieves the information is interested in that information. This is because
+ * the messaging system has different Message Channels for different types of
+ * information the applications want to communicate. When an application sends
+ * information, it doesn't randomly add the information to any channel available;
+ * it adds it to a channel whose specific purpose is to communicate that sort of
+ * information. Likewise, an application that wants to receive particular information
+ * doesn't pull info off some random channel; it selects what channel to get information
+ * from based on what type of information it wants.
+ * <p>
+ * In this example we use Apache Camel to establish two different Message Channels. The first
+ * one reads from standard input and delivers messages to Direct endpoint. The second Message  
+ * Channel is established from the Direct component to console output. No actual messages are sent, 
+ * only the established routes are printed to standard output.
+ * 
+ */
+public class App {
+
+	/**
+	 * Program entry point
+	 * @param args command line args
+	 * @throws Exception
+	 */
+	public static void main(String[] args) throws Exception {
+		CamelContext context = new DefaultCamelContext();
+		
+		context.addRoutes(new RouteBuilder() {
+
+			@Override
+			public void configure() throws Exception {
+				from("stream:in").to("direct:greetings");
+				from("direct:greetings").to("stream:out");
+			}
+		});
+		
+		context.start();
+		context.getRoutes().stream().forEach((r) -> System.out.println(r));
+		context.stop();
+	}
+}
diff --git a/message-channel/src/test/java/com/iluwatar/message/channel/AppTest.java b/message-channel/src/test/java/com/iluwatar/message/channel/AppTest.java
@@ -0,0 +1,17 @@
+package com.iluwatar.message.channel;
+
+import org.junit.Test;
+
+/**
+ * 
+ * Application test
+ *
+ */
+public class AppTest {
+	
+	@Test
+	public void test() throws Exception {
+		String[] args = {};
+		App.main(args);
+	}
+}
diff --git a/pom.xml b/pom.xml
@@ -17,6 +17,7 @@
 		<coveralls.version>3.1.0</coveralls.version>
 		<jacoco.version>0.7.2.201409121644</jacoco.version>
 		<commons-dbcp.version>1.4</commons-dbcp.version>
+		<camel.version>2.15.3</camel.version>
 	</properties>
 	<modules>
 		<module>abstract-factory</module>
@@ -75,6 +76,7 @@
     	<module>half-sync-half-async</module>
 		<module>step-builder</module>
 		<module>layers</module>
+		<module>message-channel</module>
   </modules>
 
 	<dependencyManagement>
@@ -104,6 +106,16 @@
 				<artifactId>commons-dbcp</artifactId>
 				<version>${commons-dbcp.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.apache.camel</groupId>
+				<artifactId>camel-core</artifactId>
+				<version>${camel.version}</version>
+			</dependency>
+			<dependency>
+				<groupId>org.apache.camel</groupId>
+				<artifactId>camel-stream</artifactId>
+				<version>${camel.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>junit</groupId>
 				<artifactId>junit</artifactId>
