What is the Lazy annotation impact on spring boot services Injection?

Question

I have an error about The dependencies of some of the beans in the application context form a cycle: .

and many answers suggest using @Lazy annotation to fix this problem

but what is the impact on the code after using @Lazy ??

The cycle happened because two services injected each other

and I read about @Lazy ,and how it fix this issue by @Lazy That is:

instead of fully initializing the bean, it will create a proxy to inject it into the other bean. The injected bean will only be fully created when it's first needed.

Answer 1

No matter which injection method you use, in all cases instead of a reference to a real dependency, a proxy object is provided.

It's important to understand that if a relation is marked with @Lazy it doesn't mean that creation of the dependent bean is postponed. When the dependent bean isn't marked with @Lazy itself, it will be eagerly created by the Spring container. Such behavior leads to the conclusion that lazy injection should be mainly used together with lazy initialization.

source: https://www.javacodegeeks.com/2018/03/spring-lazy-annotation-use-cases.html

Answer 2

This is to add to Abdalrhman's answer...

The @Lazy annotation is used to delay the initialization of a bean.

Delay until when? When it is needed. The inverse, if a bean is not annotated with @Lazy , its proxy object initializes it when the proxy object is initialized (on application context initialization). If a bean is annotated with @Lazy , its proxy object is still be initialized on application context initialization, but it underlying object is not initialized until an instance is requested. If it is a singleton bean, then the value is cached for later.

Why? It can be useful in situations where creating a bean is time-consuming or resource-intensive.

Note: You can make a single bean lazily-initialized by annotating the method. You can make all beans in a class (eg, @Configuration ) lazily-initialized by annotating the class.

Resources:

• https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/annotation/Lazy.html
• https://www.baeldung.com/spring-lazy-annotation

Fun fact: Some DI frameworks use lazy-initialization by default, specifically, Guice and HK2.