[Source] Java annotations@PostConstruct and detailed explanations and examples of @PreDestroy

PostConstruct annotations are used on methods that need to be executed after dependency injection is complete to perform any initialization. This method must be called before putting the class into the service. All classes that support dependency injection must support this annotation. Even if the class doesn't request any resource injection, the method annotated with PostConstruct must be called. There is only one way to annotate with this annotation. The method for applying PostConstruct annotations must adhere to all of the following criteria: the method must not have any parameters unless in the case of an EJB interceptor, as defined by the EJB specification, in which case it will come with an InvocationContext object; The return type of the method must be void; The method must not throw a checked exception; The method of applying PostConstruct can be public, protected, package private, or private; The method cannot be static except for the application client; The method can be final; If the method throws an unchecked exception, then the class must not be placed in the service unless it is an EJB that can handle the exception and recover from it.