java - Spring's InitializingBean, CommandLineRunner, ApplicationContextEvent and javax's PostConstruct

Question

This question is about the behavioural differences between Spring's

• InitializingBean's afterPropertiesSet()
• CommandLineRunner's init()
• ApplicationContextEvent and
• javax's @PostConstruct

For @PostConstruct it guarantees that it will be executed one and only once after the target bean has been fully loaded with required dependencies, reason being , if we go by custom logic from within constructor the Spring bean is not yet fully initialized and might throw NullPointerExceptions. Does this handles any circular dependencies?

Does InitializingBean guarantees the same? How is it different from @PostConstruct? Does InitializingBean provides any ordering?

Suppose in my app, I need to check if some test-users are there in database or not, if not app should create it on startup or logging the env variables. Where should these process should ideally be written into?

For ApplicationContextEvent, Spring says, "raising an event on ApplicationContext startup or refresh" but how is it different from @PostConstruct and org.springframework.boot.CommandLineRunner#run.

Also, how will these behave in case of 'hot' swap or refresh?

Answer 1

等待大神解答