Professional Java EE Design Patterns

3 Façade Pattern

WHAT’S IN THIS CHAPTER?            

• An introduction to the intent of the façade pattern
• A brief discussion of the benefits that the pattern brings
• Three ways that the pattern can be implemented: POJO, stateless, and stateful session bean façade
• The important differences between the stateful and the stateless session bean façade
• When and where to use this pattern
• Warnings about its use and potential pitfalls

WROX.COM CODE DOWNLOADS FOR THIS CHAPTER

The wrox.com code downloads for this chapter are found at www.wrox.com/go/projavaeedesignpatterns on the Download Code tab. The code is in the Chapter 3 download and individually named according to the names throughout the chapter.

The façade pattern is one of the structural design patterns described in the GoF¹ book. The intent behind it is to encapsulate complicated business logic in a higher-level interface that makes access to a subsystem easier to use. This is often done by grouping related method calls and invoking them sequentially from one method.

From a higher-level view, every API can be considered an implementation of the façade pattern since they provide a simple interface which hides its complexity. Any call to an API’s method results in the invocation of many other methods from a subsystem hidden behind it. An example of a façade would be the javax.servlet.http.HttpSession interface. This hides the complicated logic associated with maintaining the session while exposing its functionality via a handful ...