옵션 처리

주입할 스프링 빈이 없어도 동작해야 할 때가 있는데, @Autowired 만 사용시 required 옵션 기본값이 true로 되어 있어서 자동 주입 대상이 없으면 오류가 발생한다.

자동 주입 대상을 옵션으로 처리하는 방법)
· @Autowired(required=false) : 자동 주입 대상이 없으면 수정자 메서드 자체가 호출 안됨
· org.springframework.lang.@Nullable : 자동 주입 대상이 없으면 null 입력됨
· Optional<> : 자동 주입 대상이 없으면 Optional.empty 입력됨

- src/test/java/hello/core/autowired/AutowiredTest.java

package hello.core.autowired;

import hello.core.member.Member;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.lang.Nullable;

import java.util.Optional;

public class AutowiredTest {

    @Test
    void AutowiredOption() {
        ApplicationContext ac = new AnnotationConfigApplicationContext(TestBean.class);
    }

    static class TestBean {

        // 호출 안됨
        @Autowired(required = false)
        public void setNoBean1(Member member) {
            System.out.println("setNoBean1 = " + member);
        }

        // null 호출
        @Autowired
        public void setNoBean2(@Nullable Member member) {
            System.out.println("setNoBean2 = " + member);
        }

        // Optional.empty 호출
        @Autowired(required = false)
        public void setNoBean3(Optional<Member> member) {
            System.out.println("setNoBean3 = " + member);
        }

    }

}

Member는 스프링 빈이 아니기 때문에 주입이 안된다.

- 콘솔 (출력 결과)

setNoBean2 = null
setNoBean3 = Optional.empty

* 참고
@Nullable, Optional은 스프링 전반에 걸쳐서 지원된다.
-> 생성자 자동 주입에서 특정 필드에만 사용해도 된다.


참고링크 : https://www.inflearn.com/course/%EC%8A%A4%ED%94%84%EB%A7%81-%ED%95%B5%EC%8B%AC-%EC%9B%90%EB%A6%AC-%EA%B8%B0%EB%B3%B8%ED%8E%B8?cid=325969

스프링 핵심 원리 - 기본편| 김영한 - 인프런 강의