Spring DI via constructor

A simple Spring example to show you how to dependency inject a bean via Constructor method

WildAnimal.java – Interface backbone using which dependency injection is done.



package com.mahesh.ioc;

public interface WildAnimal {

    public String sound() ;

}

Lion.java – Implements the above interface and becomes a possible candidate for injection.

package com.mahesh.ioc;

public class Lion implements WildAnimal {

    public String sound() {
        return "Roar";
    }

}

Wolf.java – another implementation of interface.

package com.mahesh.ioc;

public class Wolf implements WildAnimal {

    public String sound() {
        return "Howl";
    }

}

Zoo.java – Zoo depends on WildAnimal and uses setter injection.

package com.mahesh.ioc;

public class Zoo {
    private WildAnimal wild;

    public  Zoo (WildAnimal  wild) {
        this.wild = wild;
    }

    public void testSound() {
        System.out.println(wild.sound());
    }  

}

spring-context.xml – gives the configuration information to the spring container. In spring configuration we declare the chosen implementation to supply at runtime.

<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>

<bean id="wild" class="com.mahesh.ioc.wolf" />

<bean id="zoo" class="com.mahesh.ioc.zoo" />
    <constructor-arg>
         <ref bean="wild" />
     </constructor-arg>
 </bean>

</beans>

Test.java – loads the spring configuration and gets the bean.

package com.mahesh.ioc;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {

    public static void main(String[] args) {

        ApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");
        Zoo zoo = (Zoo) context .getBean("zoo");
        zoo.testSound();

    }
}