BAEL-2755: Added design-patterns-2 module

patterns/design-patterns-2/pom.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+    <artifactId>design-patterns-2</artifactId>
+    <version>1.0</version>
+    <name>design-patterns-2</name>
+	<packaging>jar</packaging>
+	
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>patterns</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>..</relativePath>
+    </parent>
+
+    <dependencies>
+    </dependencies>
+    
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+</project>

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/JmsRouter.java

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+package com.baeldung.nullobject;
+
+public class JmsRouter implements Router {
+
+    @Override
+    public void route(Message msg) {
+        System.out.println("Routing to a JMS queue. Msg: " + msg);
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/Message.java

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+package com.baeldung.nullobject;
+
+public class Message {
+
+    private String body;
+
+    private String priority;
+
+    public Message(String body, String priority) {
+        this.body = body;
+        this.priority = priority;
+    }
+
+    public String getPriority() {
+        return priority;
+    }
+
+    @Override
+    public String toString() {
+        return "{body='" + body + '\'' +
+                ", priority='" + priority + '\'' +
+                '}';
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/NullRouter.java

@@ -0,0 +1,10 @@
+package com.baeldung.nullobject;
+
+public class NullRouter implements Router {
+
+    @Override
+    public void route(Message msg) {
+        // do nothing
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/Router.java

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+package com.baeldung.nullobject;
+
+public interface Router {
+
+    void route(Message msg);
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/RouterFactory.java

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+package com.baeldung.nullobject;
+
+public class RouterFactory {
+
+    public static Router getRouterForMessage(Message msg) {
+
+        if (msg.getPriority() == null) {
+            return new NullRouter();
+        }
+
+        switch (msg.getPriority()) {
+            case "high":
+                return new SmsRouter();
+
+            case "medium":
+                return new JmsRouter();
+
+            default:
+                return new NullRouter();
+        }
+
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/RoutingHandler.java

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+package com.baeldung.nullobject;
+
+import java.util.Arrays;
+import java.util.List;
+
+public class RoutingHandler {
+
+    public void handle(Iterable<Message> messages){
+        for (Message msg : messages) {
+            Router router = RouterFactory.getRouterForMessage(msg);
+            router.route(msg);
+        }
+    }
+
+    public static void main(String[] args) {
+        Message highPriorityMsg = new Message("Alert!", "high");
+        Message mediumPriorityMsg = new Message("Warning!", "medium");
+        Message lowPriorityMsg = new Message("Take a look!", "low");
+        Message nullPriorityMsg = new Message("Take a look!", null);
+
+        List<Message> messages = Arrays.asList(highPriorityMsg,
+                mediumPriorityMsg,
+                lowPriorityMsg,
+                nullPriorityMsg);
+
+        RoutingHandler routingHandler = new RoutingHandler();
+        routingHandler.handle(messages);
+
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/SmsRouter.java

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+package com.baeldung.nullobject;
+
+public class SmsRouter implements Router {
+
+    @Override
+    public void route(Message msg) {
+        System.out.println("Routing to a SMS gateway. Msg: " + msg);
+    }
+
+}