[Spring] Exploring Lazy and Eager Initialization of Spring Framework Beans

Exploring Lazy and Eager Initialization of Spring Framework Beans

/ @Lazy /

• Default initialization for Spring Beans : Eager
• Eager initialization is recommended:
  • Errors in the configuration are discovered immediately at application startup
• However, you can configure beans to be lazily initialized using Lazy annotation
  • NOT recommended (AND) Not frequently used
• Lazy annotation::
  • Can be used almost everywhere @Component and @Bean are used
  • Lazy-resolution proxy will be injected instead of actual dependency
  • Can be used on Configuration(@Configuration) class:
    • All @Bean methods within the @Configuration will be lazily initialized

import java.util.Arrays;  
  
@Component  
class ClassA {  
}  
@Component  
@Lazy  
class ClassB {  
    private ClassA classA;  
  
    public ClassB(ClassA classA) {  
        //Logic  
        System.out.println("Some Initialization logic");  
        this.classA = classA;  
    }  
}  
  
@Configuration  
@ComponentScan  
public class LazyInitializationLauncherApplication {  
  
    public static void main(String[] args) {  
  
        var context =  
                new AnnotationConfigApplicationContext(LazyInitializationLauncherApplication.class);  
//        Arrays.stream(context.getBeanDefinitionNames())  
//                .forEach(System.out::println);  
  
  
    }  
}

Comparing Lazy Initialization vs Eager Initialiation

Heading	Lazy Initialization	Eager Initialization
Initialization time	Bean initialized when it is first made use of in the application	Bean initializaed at startup of the application
Default	NOT Default	Default
Code Snippet	@Lazy OR @Lazy(value = ture)	@Layz(value=false) OR (Absence of @Lazy)
What happens if there are errors in initializing?	Errors will result in runtime exceptions	Errors will prevent application from starting up
Usage	Rarely used	Very frequently used
Memory Consumption	Less (until bean is initialized)	All beans are initialized at start up
Recommended Scenario	Beans very rarely used in your app	Most of your beans

정리

• @Lazy 를 선언하면 Class B를 사용하기 전까지는 생성자 초기화 실행이 안됨
• 일반적으로 추천안함 -> 오류나 버그 같은거 초기에 알 수 가 없음
• 물론 더 이상 업데이트가 없고 오류나 버그에 100퍼센트 자신 있거나 한게 아니라면 비추천이라고 한다.
• 심각한 성능저하에 대한 최적화 과정에는 필요할 수 있다.

If you have a lot of complex initialization logic and if you don't want it to delay this startup.
In those kind of situations, you can think about lazy initialization of spring beans.
However, it is very, very important to remember that if you are making use of lazy initialization errors in spring configuration will not be discovered at application startup.
They will become runtime errors.