spring core : singleton container

spring-core/basic/src/main/java/com/example/basic/AppConfig.java

@@ -17,16 +17,19 @@ public class AppConfig {
 
     @Bean
     public MemberService memberService() {
+        System.out.println("call AppConfig.memberService");
         return new MemberServiceImpl(memberRepository());
     }
 
     @Bean
     public MemberRepository memberRepository() {
+        System.out.println("call AppConfig.memberRepository");
         return new MemoryMemberRepository();
     }
 
     @Bean
     public OrderService orderService() {
+        System.out.println("call AppConfig.orderService");
         return new OrderServiceImpl(memberRepository(), discountPolicy());
     }
 

spring-core/basic/src/main/java/com/example/basic/member/MemberServiceImpl.java

@@ -17,4 +17,9 @@ public class MemberServiceImpl implements MemberService {
     public Member findMember(Long memberId) {
         return memberRepository.findById(memberId);
     }
+
+    // 테스트 용
+    public MemberRepository getMemberRepository() {
+        return memberRepository;
+    }
 }

spring-core/basic/src/main/java/com/example/basic/order/OrderServiceImpl.java

@@ -20,4 +20,9 @@ public class OrderServiceImpl implements OrderService {
         int discountPrice = discountPolicy.discount(member, itemPrice);
         return new Order(memberId, itemName, itemPrice, discountPrice);
     }
+
+    // 테스트 용
+    public MemberRepository getMemberRepository() {
+        return memberRepository;
+    }
 }

spring-core/basic/src/test/java/com/example/basic/singleton/ConfigurationSingletonTest.java

@@ -0,0 +1,39 @@
+package com.example.basic.singleton;
+
+import com.example.basic.AppConfig;
+import com.example.basic.member.MemberRepository;
+import com.example.basic.member.MemberServiceImpl;
+import com.example.basic.order.OrderServiceImpl;
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+
+class ConfigurationSingletonTest {
+
+    @Test
+    void configurationTest() {
+        ApplicationContext ac = new AnnotationConfigApplicationContext(AppConfig.class);
+
+        MemberServiceImpl memberService = ac.getBean("memberService", MemberServiceImpl.class);
+        OrderServiceImpl orderService = ac.getBean("orderService", OrderServiceImpl.class);
+        MemberRepository memberRepository = ac.getBean("memberRepository", MemberRepository.class);
+
+        MemberRepository memberRepository1 = memberService.getMemberRepository();
+        MemberRepository memberRepository2 = orderService.getMemberRepository();
+        System.out.println("memberRepository1 = " + memberRepository1);
+        System.out.println("memberRepository2 = " + memberRepository2);
+        System.out.println("memberRepository = " + memberRepository);
+
+        Assertions.assertThat(memberService.getMemberRepository()).isSameAs(memberRepository);
+        Assertions.assertThat(orderService.getMemberRepository()).isSameAs(memberRepository);
+    }
+
+    @Test
+    void configurationDeep() {
+        ApplicationContext ac = new AnnotationConfigApplicationContext(AppConfig.class);
+        AppConfig bean = ac.getBean(AppConfig.class);
+
+        System.out.println("bean = " + bean.getClass());
+    }
+}

spring-core/basic/src/test/java/com/example/basic/singleton/SingletonService.java

@@ -0,0 +1,16 @@
+package com.example.basic.singleton;
+
+public class SingletonService {
+
+    private static final SingletonService instance = new SingletonService();
+
+    private SingletonService() {}
+
+    public static SingletonService getInstance() {
+        return instance;
+    }
+
+    public void logic() {
+        System.out.println("싱클톤 객체 호출");
+    }
+}

spring-core/basic/src/test/java/com/example/basic/singleton/SingletonTest.java

@@ -0,0 +1,61 @@
+package com.example.basic.singleton;
+
+import com.example.basic.AppConfig;
+import com.example.basic.member.MemberService;
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+
+import static org.assertj.core.api.Assertions.*;
+
+public class SingletonTest {
+
+    @Test
+    @DisplayName("스프링 없는 DI 컨테이너")
+    void pureContainer() {
+        AppConfig appConfig = new AppConfig();
+
+        // 호출 할 때마다 객체를 생성
+        MemberService memberService1 = appConfig.memberService();
+        MemberService memberService2 = appConfig.memberService();
+
+        // 참조 값이 다른 것을 확인
+        System.out.println("memberService1 = " + memberService1);
+        System.out.println("memberService2 = " + memberService2);
+
+        // memberService1 != memberService2
+        assertThat(memberService1).isNotSameAs(memberService2);
+    }
+
+    @Test
+    @DisplayName("싱글톤 패턴 적용한 객체 사용")
+    void singletonServiceTest() {
+        SingletonService singletonService1 = SingletonService.getInstance();
+        SingletonService singletonService2 = SingletonService.getInstance();
+
+        System.out.println("singletonService1 = " + singletonService1);
+        System.out.println("singletonService2 = " + singletonService2);
+
+        // memberService1 != memberService2
+        assertThat(singletonService1).isSameAs(singletonService2);
+    }
+
+    @Test
+    @DisplayName("스프링 컨테이너와 싱글톤")
+    void springContainer() {
+
+        AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext(AppConfig.class);
+
+        // 호출 할 때마다 객체를 생성
+        MemberService memberService1 = ac.getBean("memberService", MemberService.class);
+        MemberService memberService2 = ac.getBean("memberService", MemberService.class);
+
+        // 참조 값이 다른 것을 확인
+        System.out.println("memberService1 = " + memberService1);
+        System.out.println("memberService2 = " + memberService2);
+
+        // memberService1 != memberService2
+        assertThat(memberService1).isSameAs(memberService2);
+    }
+}

spring-core/basic/src/test/java/com/example/basic/singleton/StatefulService.java

@@ -0,0 +1,15 @@
+package com.example.basic.singleton;
+
+public class StatefulService {
+
+    private int price; // 상태를 유지하는 필드
+
+    public void order(String name, int price) {
+        System.out.println("name = " + name + " price = " + price);
+        this.price = price;
+    }
+
+    public int getPrice() {
+        return price;
+    }
+}

spring-core/basic/src/test/java/com/example/basic/singleton/StatefulServiceTest.java

@@ -0,0 +1,36 @@
+package com.example.basic.singleton;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+
+class StatefulServiceTest {
+
+    @Test
+    void statefulServiceSingleton() {
+        ApplicationContext ac = new AnnotationConfigApplicationContext(TestConfig.class);
+        StatefulService statefulService1 = ac.getBean(StatefulService.class);
+        StatefulService statefulService2 = ac.getBean(StatefulService.class);
+
+        // A 사용자 10000원 주문
+        statefulService1.order("userA", 10000);
+        // B 사용자 20000원 주문
+        statefulService2.order("userB", 20000);
+
+        // 사용자 A 주문 금액 조회
+        int price = statefulService1.getPrice();
+        System.out.println("price = " + price);
+
+        Assertions.assertThat(statefulService1.getPrice()).isEqualTo(20000);
+    }
+
+    static class TestConfig {
+
+        @Bean
+        public StatefulService statefulService() {
+            return new StatefulService();
+        }
+    }
+}