Professional Java EE Design Patterns

4 Singleton Pattern

WHAT’S IN THIS CHAPTER?            

• The different ways that a developer can implement the singleton design pattern, besides its common usage and pitfalls
• The problems that using static members and methods causes in multithreaded environments
• The advances that were made in Java 5 SE with the introduction of the enum type and how it can be used to create thread-safe singletons
• The use of the @Singleton annotation in Java EE and how this has radically changed the way the singleton pattern is implemented in session beans
• The use of BEAN- and CONTAINER-managed concurrency and how the @LockType annotation controls access to business methods
• The main issues that have dogged the singleton pattern and why it is considered an anti-pattern that has fallen out of favor

WROX.COM CODE DOWNLOADS FOR THIS CHAPTER

The wrox.com code download for this chapter is found at www.wrox.com/go/projavaeedesignpatterns on the Download Code tab. The code is in the Chapter 4 download and individually named according to the names throughout the chapter.

The singleton pattern is one of the easiest, most well-known design patterns, but it has fallen out of fashion. Some even consider it as an anti-pattern, which will be discussed later in this chapter. However, enterprise frameworks such as Spring make heavy use of it, and Java EE offers an elegant and easy-to-use implementation. In this chapter, you will see why singletons are needed, why they fell out of fashion, how they can ...