Constructor and setter based Dependency injection code example

spring-boot/dependency-injection/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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-starter-parent</artifactId>
+		<version>2.1.4.RELEASE</version>
+		<relativePath /> <!-- lookup parent from repository -->
+	</parent>
+	<groupId>com.example</groupId>
+	<artifactId>Example</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<name>Example</name>
+	<description>Demo project for dependency injection</description>
+
+	<properties>
+		<java.version>1.8</java.version>
+	</properties>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+			<exclusions>
+				<exclusion>
+					<groupId>org.junit.vintage</groupId>
+					<artifactId>junit-vintage-engine</artifactId>
+				</exclusion>
+			</exclusions>
+		</dependency>
+		<dependency>
+			<groupId>org.mockito</groupId>
+			<artifactId>mockito-core</artifactId>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-maven-plugin</artifactId>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>

spring-boot/dependency-injection/src/main/java/com/example/ExampleApplicationCI.java

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+package com.example;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.ApplicationContext;
+
+import com.example.constructorinjection.Cake;
+
+@SpringBootApplication(scanBasePackages= {"com.example.constructorinjection","com.example.dependency"})
+public class ExampleApplicationCI  {
+
+	private static Logger LOGGER=LoggerFactory.getLogger(ExampleApplicationCI.class);
+	public static void main(String[] args) {
+		
+		ApplicationContext context = SpringApplication.run(ExampleApplicationCI.class, args);
+		Cake obj = context.getBean(Cake.class);
+		LOGGER.info("Cake : "+ obj.toString());
+	}
+
+}

spring-boot/dependency-injection/src/main/java/com/example/ExampleApplicationSI.java

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+package com.example;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.ApplicationContext;
+
+import com.example.setterinjection.Cake;
+
+@SpringBootApplication(scanBasePackages= {"com.example.setterinjection","com.example.dependency"})
+public class ExampleApplicationSI  {
+
+	private static Logger LOGGER=LoggerFactory.getLogger(ExampleApplicationSI.class);
+	public static void main(String[] args) {
+		
+		ApplicationContext context = SpringApplication.run(ExampleApplicationSI.class, args);
+		Cake obj = context.getBean(Cake.class);
+		LOGGER.info("Cake : "+ obj.toString());
+	}
+
+}

spring-boot/dependency-injection/src/main/java/com/example/constructorinjection/Cake.java

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+package com.example.constructorinjection;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Component;
+
+import com.example.dependency.Flavor;
+
+
+@Component
+public class Cake {
+
+	private static Logger LOGGER = LoggerFactory.getLogger(Cake.class);
+
+
+	private Flavor flavor;
+
+	public Cake(Flavor flavor) throws IllegalAccessException {
+		
+		//check if the required dependency is not null
+		if (flavor != null) {
+			this.flavor = flavor;
+			LOGGER.info("Flavor from Constructor Injection : " + flavor);
+		} else {
+			throw new IllegalArgumentException("Cake cannot be created with null flavor object");
+		}
+	}
+
+	public Flavor getFlavor() {
+		return flavor;
+	}
+	
+	@Override
+	public String toString() {
+		return "Cake [flavor=" + flavor + "]";
+	}
+
+}

spring-boot/dependency-injection/src/main/java/com/example/dependency/Flavor.java

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+package com.example.dependency;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class Flavor {
+	
+	String flavorType = " Chocolate ";
+	String color = " White ";
+	
+	public String getFlavorType() {
+		return flavorType;
+	}
+	
+	public String getColor() {
+		return color;
+	}
+
+	@Override
+	public String toString() {
+		return "Flavor [flavorType=" + flavorType + ", color=" + color + "]";
+	}
+	
+
+}

spring-boot/dependency-injection/src/main/java/com/example/dependency/Topping.java

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+package com.example.dependency;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class Topping {
+
+	private String toppingName;
+
+	public String getToppingName() {
+		return toppingName;
+	}
+
+	public void setToppingName(String toppingName) {
+		this.toppingName = toppingName;
+	}
+
+	@Override
+	public String toString() {
+		return "Topping [toppingName=" + toppingName + "]";
+	}
+
+
+}

spring-boot/dependency-injection/src/main/java/com/example/setterinjection/Cake.java

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+package com.example.setterinjection;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import com.example.dependency.Flavor;
+import com.example.dependency.Topping;
+
+@Component
+public class Cake {
+
+	private Logger LOGGER = LoggerFactory.getLogger(Cake.class);
+	
+	private Flavor flavor;
+	
+	@Autowired
+	private Topping toppings;
+	
+	public Cake() {
+		LOGGER.info("Flavor from setter Injection : " + this.flavor);
+	}
+	
+	@Autowired
+	public void setFlavor(Flavor flavor) {
+		LOGGER.info("Initialising flavor object using setter injection");
+		this.flavor = flavor;
+	}
+
+	public Flavor getFlavor() {
+		return flavor;
+	}
+
+	public Topping getToppings() {
+		return toppings;
+	}
+
+	public void setToppings(Topping toppings) {
+		this.toppings = toppings;
+	}
+
+	@Override
+	public String toString() {
+		return "Cake [LOGGER=" + LOGGER + ", flavor=" + flavor + ", toppings=" + toppings + "]";
+	}
+
+
+
+}

spring-boot/dependency-injection/src/main/resources/application.properties

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+spring.main.web-application-type=none
+spring.main.banner-mode=off

spring-boot/dependency-injection/src/test/java/com/example/test/constructorinjection/TestCakeClassConstructorInjection.java

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+package com.example.test.constructorinjection;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import com.example.ExampleApplicationCI;
+import com.example.constructorinjection.Cake;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringBootTest(classes = ExampleApplicationCI.class)
+public class TestCakeClassConstructorInjection {
+
+	@Autowired
+	Cake cake;
+	
+	@Test
+	public void testConstructorInjection() {	
+		String testColor=cake.getFlavor().getColor();
+		Assert.assertEquals(testColor, " White ");
+	}
+}

spring-boot/dependency-injection/src/test/java/com/example/test/setterinjection/TestCakeClassSetterInjection.java

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+package com.example.test.setterinjection;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import com.example.ExampleApplicationSI;
+import com.example.setterinjection.Cake;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringBootTest(classes = ExampleApplicationSI.class)
+public class TestCakeClassSetterInjection {
+
+	@Autowired
+	Cake cake;
+
+	@Test
+	public void testSetterInjection() {
+		String testColor = cake.getFlavor().getColor();
+		Assert.assertEquals(testColor, " White ");
+		String toppingsName=cake.getToppings().getToppingName();
+		
+		//check if the dependency is not null
+		if(toppingsName!=null) {
+			Assert.assertEquals(toppingsName, "gems");
+		}
+		
+	}
+}