Bael 1366 dagger2 (#4288)

* BAEL-1366-dagger2: Added Dagger 2 example and test case. Added dependency and Dagger compiler plugin to pom.

dagger/README.md

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+### Relevant articles

dagger/pom.xml

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+<?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>dagger</artifactId>
+    <name>dagger</name>
+
+    <parent>
+        <artifactId>parent-modules</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit.version}</version>
+            <scope>test</scope>
+        </dependency>
+        
+        <!-- Dagger 2 -->
+        <dependency>
+    		<groupId>com.google.dagger</groupId>
+    		<artifactId>dagger</artifactId>
+    		<version>${dagger.version}</version>
+  		</dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <!-- Annotation processor for Dagger 2 -->
+             <plugin>
+     		 	<groupId>org.apache.maven.plugins</groupId>
+      			<artifactId>maven-compiler-plugin</artifactId>
+      			<version>3.6.1</version>
+      			<configuration>
+        			<annotationProcessorPaths>
+          				<path>
+            				<groupId>com.google.dagger</groupId>
+            				<artifactId>dagger-compiler</artifactId>
+            				<version>2.16</version>
+          				</path>
+        			</annotationProcessorPaths>
+      			</configuration>
+    		</plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <junit.version>4.12</junit.version>
+        <dagger.version>2.16</dagger.version>
+    </properties>
+
+</project>

dagger/src/main/java/com/baeldung/dagger/intro/Brand.java

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+package com.baeldung.dagger.intro;
+
+/**
+ * Brand of a {@link Car}.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class Brand {
+
+	/**
+	 * The name of the brand.
+	 */
+	private String name;
+
+	/**
+	 * Instantiates a new Brand.
+	 *
+	 * @param name
+	 *            the {@link #name}
+	 */
+	public Brand(String name) {
+		this.name = name;
+	}
+
+	/**
+	 * Gets the {@link #name}.
+	 *
+	 * @return the {@link #name}
+	 */
+	public String getName() {
+		return name;
+	}
+
+	/**
+	 * Sets the {@link #name}.
+	 *
+	 * @param name
+	 *            the new {@link #name}
+	 */
+	public void setName(String name) {
+		this.name = name;
+	}
+
+}

dagger/src/main/java/com/baeldung/dagger/intro/Car.java

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+package com.baeldung.dagger.intro;
+
+import javax.inject.Inject;
+
+/**
+ * Represents a car.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class Car {
+
+	/**
+	 * The car's engine.
+	 */
+	private Engine engine;
+
+	/**
+	 * The car's brand.
+	 */
+	private Brand brand;
+
+	/**
+	 * Instantiates a new Car.
+	 *
+	 * @param engine
+	 *            the {@link #engine}
+	 * @param brand
+	 *            the {@link #brand}
+	 */
+	@Inject
+	public Car(Engine engine, Brand brand) {
+		this.engine = engine;
+		this.brand = brand;
+	}
+
+	/**
+	 * Gets the {@link #engine}.
+	 *
+	 * @return the {@link #engine}
+	 */
+	public Engine getEngine() {
+		return engine;
+	}
+
+	/**
+	 * Sets the {@link #engine}.
+	 *
+	 * @param engine
+	 *            the new {@link #engine}
+	 */
+	public void setEngine(Engine engine) {
+		this.engine = engine;
+	}
+
+	/**
+	 * Gets the {@link #brand}.
+	 *
+	 * @return the {@link #brand}
+	 */
+	public Brand getBrand() {
+		return brand;
+	}
+
+	/**
+	 * Sets the {@link #brand}.
+	 *
+	 * @param brand
+	 *            the new {@link #brand}
+	 */
+	public void setBrand(Brand brand) {
+		this.brand = brand;
+	}
+
+}

dagger/src/main/java/com/baeldung/dagger/intro/Engine.java

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+package com.baeldung.dagger.intro;
+
+/**
+ * Engine of a {@link Car}.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class Engine {
+
+	/**
+	 * Starts the engine.
+	 */
+	public void start() {
+		System.out.println("Engine started");
+	}
+
+	/**
+	 * Stops the engine.
+	 */
+	public void stop() {
+		System.out.println("Engine stopped");
+	}
+}

dagger/src/main/java/com/baeldung/dagger/intro/VehiclesComponent.java

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+package com.baeldung.dagger.intro;
+
+import javax.inject.Singleton;
+
+import dagger.Component;
+
+/**
+ * Dagger component for building vehicles.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+@Singleton
+@Component(modules = VehiclesModule.class)
+public interface VehiclesComponent {
+
+	/**
+	 * Builds a {@link Car}.
+	 * 
+	 * @return a {@link Car}
+	 */
+	public Car buildCar();
+
+}

dagger/src/main/java/com/baeldung/dagger/intro/VehiclesModule.java

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+package com.baeldung.dagger.intro;
+
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+/**
+ * Dagger module for providing vehicles components.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+@Module
+public class VehiclesModule {
+
+	/**
+	 * Creates an {@link Engine}.
+	 * 
+	 * @return an {@link Engine}
+	 */
+	@Provides
+	public Engine provideEngine() {
+		return new Engine();
+	}
+
+	/**
+	 * Creates a {@link Brand}.
+	 * 
+	 * @return a {@link Brand}
+	 */
+	@Provides
+	@Singleton
+	public Brand provideBrand() {
+		return new Brand("Baeldung");
+	}
+}

dagger/src/test/java/com/baeldung/dagger/intro/DaggerUnitTest.java

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+package com.baeldung.dagger.intro;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit test for building a {@link Car} using Dagger.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class DaggerUnitTest {
+	
+	/**
+	 * Builds two {@link Car} and checks that the fields are injected correctly.
+	 */
+	@Test
+	public void givenGeneratedComponent_whenBuildingCar_thenDependenciesInjected() {
+		VehiclesComponent component = DaggerVehiclesComponent.create();
+		
+		Car carOne = component.buildCar();
+		Car carTwo = component.buildCar();
+		
+		Assert.assertNotNull(carOne);
+		Assert.assertNotNull(carTwo);
+		Assert.assertNotNull(carOne.getEngine());
+		Assert.assertNotNull(carTwo.getEngine());
+		Assert.assertNotNull(carOne.getBrand());
+		Assert.assertNotNull(carTwo.getBrand());
+		Assert.assertNotEquals(carOne.getEngine(), carTwo.getEngine());
+		Assert.assertEquals(carOne.getBrand(), carTwo.getBrand());
+	}
+
+}