Spring DI via constructor

Uses Spring to dependency inject a bean via constructor.

1. IOutputGenerator

An interface and implementation class of it.

package com.mkyong.output;

public interface IOutputGenerator
{
    public void generateOutput();
}

package com.mkyong.output.impl;

import com.mkyong.output.IOutputGenerator;

public class JsonOutputGenerator implements IOutputGenerator
{
    public void generateOutput(){
        System.out.println("This is Json Output Generator");
    }
}

2. Helper class

A helper class, later use Spring to DI the IOutputGenerator, via constructor.

package com.mkyong.output;

import com.mkyong.output.IOutputGenerator;

public class OutputHelper {
    IOutputGenerator outputGenerator;

    public void generateOutput() {
        outputGenerator.generateOutput();
    }

    //DI via constructor
    public OutputHelper(IOutputGenerator outputGenerator){
        this.outputGenerator = outputGenerator;
    }

}

3. Spring configuration

See below Spring bean configuration, Spring will DI above “JsonOutputGenerator” into this “OutputHelper” class, via constructor “public OutputHelper(IOutputGenerator outputGenerator)“.

<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-2.5.xsd">

    <bean id="OutputHelper" class="com.mkyong.output.OutputHelper">
        <constructor-arg>
            <ref bean="JsonOutputGenerator" />
        </constructor-arg>
    </bean>

    <bean id="JsonOutputGenerator" class="com.mkyong.output.impl.JsonOutputGenerator" />

</beans>

4. Run it

Load everything, and run it.

package com.mkyong.common;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.mkyong.output.OutputHelper;

public class App {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext(
                "SpringBeans.xml");

        OutputHelper output = (OutputHelper)context.getBean("OutputHelper");
                output.generateOutput();
    }
}

Output

This is Json Output Generator