What design patterns are used in EJB?

1. Factory Method:
Define a interface for creating classes, let a subclass (or a helper class) decide which class to    instantiate.This is used in EJB creation model. EJBHome defines an interface for creating the EJBObject implementations. They are actually created by a generated container class. See InitialContextFactory interface that returns an InitialContext based on a properties hashtable.
2.Singleton:
Ensure a class has only one instance, and provide a global point of access to it.
There are many such classes. One example is javax.naming.NamingManager
3. Abstract Factory: 
Provide an interface for creating families of relegated or dependent objects without specifying their concrete classes.
We have interfaces called InitialContext, InitialContextFactory. InitialContextFactory has methods to get InitialContext.
4.Builder:
Separate the construction of a complex factory from its representation so that the same construction process can create different representations.
InitialContextFactoryBuilder can create a InitialContextFactory.
5. Adapter:
Convert the interface of a class into another interface clients expect.
In the EJB implementation model, we implement an EJB in a class that extends SessionBean or a EntityBean. We don't directly implement the EJBObject/home interfaces. EJB container generates a class that adapts the EJBObject interface by forwarding the calls to the enterprise bean class and provides declarative transaction, persistence support.
6. Proxy:
Provide a surrogate for other object to control access to it.
We have remote RMI-CORBA proxies for the EJB's.
7. Memento:
Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.