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)“.

<?xml version="1.0"?>
<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