[Spring] 스프링 생성자를 통한 주입 의존성 주입(Dependency Injection)

의존성 주입(Dependency Injection)

 

의존성 주입은 Spring에서 아주 중요한 개념이자 장점

bean객체 생성시 bean 객체가 관리할 값이나 객체를 주입하는 것을 의미

bean 객체 생성 후 bean 객체가 가질 기본값을 자바코드로 설정하는 것이 아닌 bean을 정의하는

xml코드에서 정의하는 개념

 

Bean을 정의할 때 constructor-arg 태그를 이용해 주입하게 되면 생성자를 통해 주입할 수 있음.

Bean 객체를 생성할 때 객체의 기본값을 생성자를 통해 주입가능.

package sanghoon.main;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import sanghoon.beans.DataBean;
import sanghoon.beans.TestBean;
import sanghoon.beans.TestBean2;

public class MainClass {

	public static void main(String[] args) {
		
		ClassPathXmlApplicationContext ctx= new ClassPathXmlApplicationContext("sanghoon/config/beans.xml");
		
		TestBean t1= new TestBean();
		t1.printData();
		
		System.out.println("-------------------");
		
		TestBean t2= new TestBean(100);
		t2.printData();
		
		System.out.println("-------------------");
		
		TestBean t3= new TestBean(11.11);
		t3.printData();
		
		System.out.println("-------------------");
		
		
		TestBean t4 = new TestBean("문자열");
		t4.printData();
		
		System.out.println("-------------------");

		TestBean t5 = new TestBean(200,22.22,"안녕하세요");
		t5.printData();
		
		
		System.out.println("-------------------");
		
//		TestBean t6 = new TestBean("반갑습니다",300,33.33);
//		t6.printData(); -> TestBean클래스의 생성자에 정의되어있는 매개변수의 순서가 일치하지 않기때문에 에러가남 

		/*TestBeanClass 이용 ↑*/	

		
		/*beans.xml 이용 ↓ */	
		TestBean obj1 = ctx.getBean("obj1",TestBean.class);
		obj1.printData();
		
		System.out.println("-------------------");
		
		TestBean obj2 = ctx.getBean("obj2",TestBean.class);
		obj2.printData();
		
		System.out.println("-------------------");

		TestBean obj3 = ctx.getBean("obj3",TestBean.class);
		obj3.printData();
		
		
		System.out.println("-------------------");

		TestBean obj4 = ctx.getBean("obj4",TestBean.class);
		obj4.printData();
		
		System.out.println("-------------------");
		
		TestBean obj5 = ctx.getBean("obj5",TestBean.class);
		obj5.printData();
		
		TestBean obj6 = ctx.getBean("obj6",TestBean.class);
		obj6.printData();
		// beans.xml에 만들어져있는 매개변수의 순서와 달라도 정상적으로 출력됨 (자바와의 차이)
		
		TestBean obj7 = ctx.getBean("obj7",TestBean.class);
		obj7.printData();
		
		System.out.println("-------------------");
//자바코드로 할때 
		DataBean d1= new DataBean();
		DataBean d2= new DataBean();
		TestBean2 t200 = new TestBean2(d1, d2);
		t200.printData();
//beans.xml로 할 때		
		
		System.out.println("-------------------");
		
		TestBean2 obj8 = ctx.getBean("obj8",TestBean2.class);
		obj8.printData();
	
		System.out.println("-------------------");

		TestBean2 obj9 = ctx.getBean("obj9", TestBean2.class);
		obj9.printData();
		ctx.close();
	}
}

package sanghoon.beans;

public class TestBean {

	private int data1;
	private double data2;
	private String data3;

	public TestBean() {
		System.out.println("TestBean의 기본 생성자");
		this.data1=0;
		this.data2=0.0;
		this.data3=null;
	}
	
	public TestBean(int data1) {
		System.out.println("TestBean의 생성자: int 변수 1개");
		this.data1=data1;
		this.data2=0.0;
		this.data3=null;
	}
	
	public TestBean(double data2) {
		System.out.println("TestBean의 생성자: double 변수 1개");
		this.data1=0;
		this.data2=data2;
		this.data3=null;
	}
	
	public TestBean(String data3) {
		System.out.println("TestBean의 생성자: String 변수1개");
		this.data1=0;
		this.data2=0.0;
		this.data3=data3;
	}
	
	public TestBean(int data1, double data2, String data3) {
		System.out.println("TestBean의 생성자: String 변수3개");
		this.data1=data1;
		this.data2=data2;
		this.data3=data3;
	}
	
	
	public void printData() {
		System.out.printf("data1 : %d\n", data1);
		System.out.printf("data2 : %f\n", data2);
		System.out.printf("data3 : %s\n", data3);
	}

}

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>sanghoon</groupId>
	<artifactId>ConstructorDI</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<!-- xml에서 사용할 속성들 -->
	<properties>
		<!-- 자바 버전 -->
		<java-vesion>1.8</java-vesion>
		<!-- 스프링 버전 -->
		<org.springframework-version>5.1.9.RELEASE</org.springframework-version>
		<!-- <org.springframework-version>4.3.25.RELEASE</org.springframework-version> -->
		<org.slf4j-version>1.7.26</org.slf4j-version>
		<ch.qos.logback-version>1.2.3</ch.qos.logback-version>
	</properties>
	<!-- 프로젝트에서 사용할 라이브러리 정보 -->
	<dependencies>
		<!-- spring-context -->
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
			<version>${org.springframework-version}</version>
		</dependency>
		<!-- slf4j -->
		<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-api</artifactId>
			<version>${org.slf4j-version}</version>
		</dependency>
		<!-- logback -->
		<!-- https://mvnrepository.com/artifact/ch.qos.logback/logback-classic -->
		<dependency>
			<groupId>ch.qos.logback</groupId>
			<artifactId>logback-classic</artifactId>
			<version>${ch.qos.logback-version}</version>
			<exclusions>
				<exclusion>
					<groupId>org.slf4j</groupId>
					<artifactId>slf4j-api</artifactId>
				</exclusion>
			</exclusions>
			<scope>runtime</scope>
		</dependency>
	</dependencies>

</project>

<?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='obj1' class='sanghoon.beans.TestBean' lazy-init='true' />

	<bean id='obj2' class='sanghoon.beans.TestBean' lazy-init='true'>
		<constructor-arg value='100' type='int'/>
	</bean>
	
	<bean id='obj3' class='sanghoon.beans.TestBean' lazy-init='true'>
		<constructor-arg value='11.11' type='double'/>
	</bean>
	
	<bean id='obj4' class='sanghoon.beans.TestBean' lazy-init='true'>
		<constructor-arg value='문자열'/>
	</bean>
	
	<bean id='obj5' class='sanghoon.beans.TestBean' lazy-init='true'>
		<constructor-arg value='200' type='int'/>
		<constructor-arg value='22.22' type='double'/>
		<constructor-arg value='안녕하세요' type='java.lang.String'/>
	</bean>
	
	<bean id='obj6' class='sanghoon.beans.TestBean' lazy-init='true'>
		<constructor-arg value='반갑습니다' type='java.lang.String'/>
		<constructor-arg value='300' type='int'/>
		<constructor-arg value='33.33' type='double'/>
	</bean>
	
	
	<bean id='obj7' class='sanghoon.beans.TestBean' lazy-init='true'>
		<constructor-arg value='44.44' type='double' index='1'/>
		<constructor-arg value='4' type='int' index='0'/>
		<constructor-arg value='반갑습니다' type='java.lang.String' index='2'/>
	</bean>
	
	<bean id='obj8' class='sanghoon.beans.TestBean2' lazy-init='true'>
		<constructor-arg>
		<bean class='sanghoon.beans.DataBean'/>
		</constructor-arg>
		<constructor-arg>
		<bean class='sanghoon.beans.DataBean'/>
		</constructor-arg>
	</bean>
	
	<!--주입할 때 마다 자동으로 객체생성하려고 scope='prototype' 설정했음!!   --> 
	<bean id='data_bean' class='sanghoon.beans.DataBean' scope='prototype'/> 
	
	<bean id='obj9' class='sanghoon.beans.TestBean2' lazy-init='true'>
		<constructor-arg ref= 'data_bean'/>
		<constructor-arg  ref='data_bean'/>
	</bean>
	
</beans>

package sanghoon.beans;

public class TestBean2 {
	private DataBean data1;
	private DataBean data2;
	
	public TestBean2(DataBean data1,DataBean data2) {
		this.data1= data1;
		this.data2= data2;
	}

	public void printData() {
		System.out.printf("data1 : %s\n", data1);
		System.out.printf("data2 : %s\n", data2);
	}
}

package sanghoon.beans;

public class DataBean {

}