One constant truth in software development is that technology never stops
changing. It is in a company's best interest to develop software in such
a way as to protect it from, but still utilize, changing technology practices,
patterns and APIs. A common pattern in many of the Arch4J components is to
shield the application developer's implementation from the specifics of the
environment his code runs in.
The pattern as defined in an EJB environment with an example Account
service is as follows:
It looks like a lot of classes, right? The good news is that the application
developer is really only responsible for coding the AccountService interface
and the AccountServiceImpl implementation. The rest of the component specific
classes, those outlines in green, can be created with a code generator. See Arch4J's
Java Class Generator for more information
on code generation.
SessionBean, EJBHome, and EJBObject are all defined by the EJB specification
and must be implemented for each distributed component. Arch4J provides the
BaseSessionBean class which has some of the code common to most EJBs. The
AccountService class declares each distributed method to be supported by the
EJB. The AccountServiceImpl contains the actual business logic code to define
each method declared in AccountService. AccountBean and Account provide a
connecting layer to the EJB classes without forcing direct dependence. AccountBean
is simply a delegate class which forwards all calls to an instance of
AccountServiceImpl. The AccountServiceProvider is a convenience class used by
clients to get an Account remote object. It wraps the call to JNDI to get the
AccountHome and the instantiation of the remote.
Take a look at the Arch4J's example project Lunch-o-Matic for example uses of
This pattern is also useful for a project that may not want to introduce an
EJB application server initially, but that does not want to limit itself from
taking advantage of one in the future. As long as developers are careful to
isolate business code into interfaces and implementation classes and not directly
rely on services specific to the environment, they should have no trouble
porting to an EJB environment.