[Spring] DI / IoC (Bean 객체 생성_06) - 객체 참조(ref)

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패키지 구조

Emp.java

package com.test04;

public class Emp {
	
	private String name;
	private int salary;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getSalary() {
		return salary;
	}
	public void setSalary(int salary) {
		this.salary = salary;
	}
	@Override
	public String toString() {
		return "이름 : " + name + "\t 월급 : " + salary;
	}
	
}

Developer.java

package com.test04;

public class Developer {
	
	private Emp emp;
	private String dept;
	
	public Developer() {
	}
	public Developer(Emp emp, String dept) {
		this.emp = emp;
		this.dept = dept;
	}
	
	@Override
	public String toString() {
		return emp + " \t 부서 : " + dept;
	}
}

Engineer.java

package com.test04;

public class Engineer {
	
	private Emp emp;
	private String dept;
	
	public Engineer() {
	}
	public Engineer(Emp emp, String dept) {
		this.emp = emp;
		this.dept = dept;
	}
	@Override
	public String toString() {
		return emp + " \t 부서 : " + dept;
	}
	
}

beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<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.xsd">

	<bean id="lee" class="com.test04.Emp">
		<property name="name" value="이순신" />
		<property name="salary" value="3000000" />
	</bean>
	
	<bean id="hong" class="com.test04.Emp">
		<property name="name" value="홍길동" />
		<property name="salary" value="2500000" />
	</bean>
	
	<bean id="lee-ss" class="com.test04.Developer">
		<constructor-arg name="emp" ref="lee" />
		<constructor-arg name="dept" value="개발" />
	</bean>
	
	<bean id="hong-gd" class="com.test04.Engineer">
		<constructor-arg index="0" ref="hong" />
		<constructor-arg index="1" value="기술" />
	</bean>	

</beans>

MTest.java

package com.test04;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MTest {

	public static void main(String[] args) {
		ApplicationContext factory = new ClassPathXmlApplicationContext("com/test04/beans.xml");
		
		Developer lee = factory.getBean("lee-ss", Developer.class);
		Engineer hong = (Engineer) factory.getBean("hong-gd");
		
		System.out.println(lee);
		System.out.println(hong);
	}
}

실행결과

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각 클래스의 생성자와 세터의 여부에 따라 객체를 반들때 주입방식이 정말 다양해 질수 있습니다.

<bean id="lee" class="com.test04.Emp">
	<property name="name" value="이순신" />
	<property name="salary" value="3000000" />
</bean>
	
<bean id="hong" class="com.test04.Emp">
	<property name="name" value="홍길동" />
	<property name="salary" value="2500000" />
</bean>

해당 코드에서는 Emp클래스를 이용하여 lee객체와 hong객체를 만들었는데요.

이런 객체를 자식 클래스를 이용한 객체에서 참조 할 수 있습니다. ref속성으로 말이죠!

<bean id="lee-ss" class="com.test04.Developer">
	<constructor-arg name="emp" ref="lee" />
	<constructor-arg name="dept" value="개발" />
</bean>

<bean id="hong-gd" class="com.test04.Engineer">
	<constructor-arg index="0" ref="hong" />
	<constructor-arg index="1" value="기술" />
</bean>

Engineer클래스와 Developer클래스 모두 파라미터가 2개짜리인 생성자에 모면 Emp타입의 emp변수를 파라미터로 받고있습니다.

lee-ss객체와 hong-gd객체에서는 Emp타입의 emp변수에 lee객체와 hong객체를 참조하여 아규먼트로 값을 주입하였습니다!

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MTest에서도 객체를 사용할때 불러오는 방법 두가지 모두 같이 사용 할 수 있습니다.

Developer lee = factory.getBean("lee-ss", Developer.class);
Engineer hong = (Engineer) factory.getBean("hong-gd");