Added example of spring constructor based dependency injection

spring-constructor-di/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>
+
+	<groupId>baeldung</groupId>
+	<artifactId>baeldung</artifactId>
+	<version>1.0-SNAPSHOT</version>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-context</artifactId>
+			<version>4.2.6.RELEASE</version>
+		</dependency>
+		<dependency>
+			<groupId>javax.inject</groupId>
+			<artifactId>javax.inject</artifactId>
+			<version>1</version>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-compiler-plugin</artifactId>
+				<configuration>
+					<source>1.8</source>
+					<target>1.8</target>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>

spring-constructor-di/src/main/java/com/baeldung/spring/Config.java

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+package com.baeldung.spring;
+
+import com.baeldung.spring.domain.Car;
+import com.baeldung.spring.domain.Engine;
+import com.baeldung.spring.domain.Transmission;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+@ComponentScan("com.baeldung.spring")
+public class Config {
+
+    @Bean
+    public Engine engine() {
+        return new Engine("v8", 5);
+    }
+
+    @Bean
+    public Transmission transmission() {
+        return new Transmission("sliding");
+    }
+}

spring-constructor-di/src/main/java/com/baeldung/spring/SpringRunner.java

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+package com.baeldung.spring;
+
+import com.baeldung.spring.domain.Car;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.support.ClassPathXmlApplicationContext;
+
+public class SpringRunner {
+    public static void main(String[] args) {
+        Car toyota = getCarFromXml();
+
+        System.out.println(toyota);
+
+        toyota = getCarFromJavaConfig();
+
+        System.out.println(toyota);
+    }
+
+    private static Car getCarFromJavaConfig() {
+        ApplicationContext context = new AnnotationConfigApplicationContext(Config.class);
+
+        return context.getBean(Car.class);
+    }
+
+    private static Car getCarFromXml() {
+        ApplicationContext context = new ClassPathXmlApplicationContext("baeldung.xml");
+
+        return context.getBean(Car.class);
+    }
+}

spring-constructor-di/src/main/java/com/baeldung/spring/domain/Car.java

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+package com.baeldung.spring.domain;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import javax.inject.Inject;
+import javax.inject.Named;
+
+@Component
+public class Car {
+    private Engine engine;
+    private Transmission transmission;
+
+    @Autowired
+    public Car(Engine engine, Transmission transmission) {
+        this.engine = engine;
+        this.transmission = transmission;
+    }
+
+    @Override
+    public String toString() {
+        return String.format("Engine: %s Transmission: %s", engine, transmission);
+    }
+}

spring-constructor-di/src/main/java/com/baeldung/spring/domain/Engine.java

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+package com.baeldung.spring.domain;
+
+public class Engine {
+    private String type;
+    private int volume;
+
+    public Engine(String type, int volume) {
+        this.type = type;
+        this.volume = volume;
+    }
+
+    @Override
+    public String toString() {
+        return String.format("%s %d", type, volume);
+    }
+}

spring-constructor-di/src/main/java/com/baeldung/spring/domain/Transmission.java

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+package com.baeldung.spring.domain;
+
+public class Transmission {
+	private String type;
+
+	public Transmission(String type) {
+		this.type = type;
+	}
+
+	@Override
+	public String toString() {
+		return String.format("%s", type);
+	}
+}

spring-constructor-di/src/main/resources/baeldung.xml

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+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans
+    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
+
+    <bean id="toyota" class="com.baeldung.spring.domain.Car">
+        <constructor-arg index="0" ref="engine"/>
+        <constructor-arg index="1" ref="transmission"/>
+    </bean>
+
+    <bean id="engine" class="com.baeldung.spring.domain.Engine">
+        <constructor-arg index="0" value="v4"/>
+        <constructor-arg index="1" value="2"/>
+    </bean>
+
+    <bean id="transmission" class="com.baeldung.spring.domain.Transmission">
+        <constructor-arg value="sliding"/>
+    </bean>
+
+</beans>