Spring DI via constructor

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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

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