Bael 1366 dagger2 (#4288)

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

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

@@ -0,0 +1,45 @@
+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

@@ -0,0 +1,75 @@
+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

@@ -0,0 +1,24 @@
+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

@@ -0,0 +1,24 @@
+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

@@ -0,0 +1,37 @@
+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

@@ -0,0 +1,34 @@
+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());
+	}
+
+}