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