Which patterns were used by Sun in designing the Enterprise JavaBeans model?

Uma Sankar ramaraju

Many design patterns were used in EJB, and some of them are clearly identifiable by their naming convention. Here are several:

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.

Certainly this pattern is used in activating/passivating the enterprise beans by the container/server.

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