Question on Singleton Session Bean Initialization

[Mohit G Gupta]

Source: EJB 3.1 Spec.

4.8 Singleton Session Beans

A Singleton session bean is a session bean component that is instantiated once per application. In cases
where the container is distributed over many virtual machines, each application will have one bean
instance of the Singleton for each JVM.

Thus,Each Application has only one instance of Singleton Bean.

4.8.1 Singleton Initialization
In some cases, explicit initialization ordering dependencies exist between multiple Singleton compo-
nents in an application. The DependsOn annotation is used to express these dependencies. A
DependsOn dependency is used in cases where one Singleton must initialize before one or more other
Singletons. The container ensures that all Singleton beans with which a Singleton has a DependsOn
relationship have been initialized before PostConstruct is called.

However,from the above paragraph I understand that "there can be multiple Singleton's".

"The container ensures that all Singleton beans with which a Singleton has a DependsOn relationship have been initialized"

Q1. How is this possible as the topic 4.8 says that "Each Application has only one instance of Singleton Bean." ?

Please advise.

[Frits Walraven]

Q1. How is this possible as the topic 4.8 says that "Each Application has only one instance of Singleton Bean." ?

Each Application has only one instance of Singleton Bean of a certain class. There can be many Singletons in an application.

Regards,
Frits

[Mohit G Gupta]

Thanks Frits.
I understood the statement now.