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Conclusion
The Singleton pattern is an excellent candidate for any application facility that is modeled by a class that must not be instantiated more than once. As with patterns in general, it offers a simple and elegant solution to the case at hand in this article—a Provisioning Server. The ease with which the Singleton pattern can be employed helps free the developer to get a grip in solving the complex application domain issues. This provides a powerful combination of a solid pattern-based foundation and more time than usual to focus on application value-added features. It allows for better product differentiation.
I didn't look at any of the middleware code that typically forms part of our service provisioning system. Generally, this code makes use of network device technology, such as SNMP, command-line interface, etc. However, the pattern used allows for an elegant solution without initially having to worry too much about complex environmental issues. In other words, you can create much of the solution without having to concentrate on everything.
Patterns provide fertile design-level ground for top-grade software development. By solving significant generic problems, such as single instance control, patterns should become an indispensable tool for all software developers. They allow for rapid solutions to difficult recurring problems.
One aspect of patterns that particularly appeals to me is that their application can cross industry segments. In other words, if a practitioner makes an honest effort to understand and apply a wide range of patterns in his application domain, then there's a good chance that this knowledge will be portable to another industry. A patterns-literate developer could (with some additional domain training) move for example from programming telecoms to finance systems. The advent of frameworks such as Spring and other inversion of control containers helps to facilitate such cross-domain migrations. I need hardly say that the latter is especially important in these times of economic uncertainty.