Chapter 19
Controlling Access
In This Chapter
- Seeing why proxies are useful
- Recognizing different kinds of proxies
- Adding a proxy to your system
In this chapter, I tell you how to isolate a component with a proxy — specifically, the Proxy pattern. You use this pattern when a client needs the services of another component and direct communication — even though possible — isn't the best solution. The proxy component provides an indirect way to access a component to coordinate, filter, and control direct access. This may be done to increase security, enforce protocols, or speed up operations, among other things that I cover in the “Getting Acquainted with Proxy Variants” section.
Many people, including Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, authors of Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley Professional) have written versions of the Proxy pattern. In this chapter, I discuss a general version of Proxy. You may encounter many variants that refine and adapt this general version.
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