Encapsulating the business logic with a POJO façade - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 263

that does different things depending on the identity of the caller can call the
SecurityContextHolder .
Security is one of the issues you must address when developing a POJO façade.
Another is remoting.

7.2.6 Supporting remote clients

In many applications, the business tier is invoked by a presentation tier that runs
within the same JVM . However, in some applications the business tier is invoked by
a client running on a different machine. For example, an application running on
a cell phone that enables a customer to order dinner on the way home would
invoke the PlaceOrderFacade remotely. Supporting remote clients with EJB s is easy
because remote invocation is built in. It even allows EJB s to participate in transac-
tions that are initiated by remote clients. If we want a POJO façade to support
remote clients, then we have to use a separate remoting technology.
Once again the Spring framework comes to the rescue. It supports several
methods of exposing a POJO façade to a remote client:

Standard Java RMI

■

Hessian, an open source binary HTTP protocol that uses its own serializa-
tion mechanism for Java objects

■

Burlap, an open source XML over HTTP protocol that uses its own serializa-
tion mechanism for Java objects

■

Spring HTTP , an HTTP protocol provided by Spring that uses standard Java
serialization

■

Web services using the Java API for XML -based RPC ( JAX - RPC ) and Axis

■

Please note, however, that none of these technologies allows a POJO façade to par-
ticipate in a transaction initiated by a remote client. If that is one of your require-
ments, then you must use EJB s.
Spring makes it remarkably easy to expose a POJO façade to a remote client
using RMI , Hessian, Burlap, or the Spring HTTP invoker. You configure an
“exporter” Spring bean such as RMIServiceExporter , or HessianServiceExporter
takes care of the infrastructure magic required to map requests from remote cli-
ents into calls to POJO façade methods. Exposing a POJO façade as a web service is
not quite as easy because you do need to write some code, but it is still very
straightforward. For more information on using these remoting technologies with
Spring, see the Spring documentation or Spring in Action [Walls 2005].