9.1 What Are Extension Points?
Think of a framework as a house that
comes with part of the structure already complete, but gives you the
option to modify certain characteristics, such as the wallpaper and
paint colors. If the default characteristics already suit your needs,
you don't have to change anything. If you like the
paint job, for example, that's one less thing to
worry about.This is similar to how a framework functions, and
that's a big advantage when building applications.
If functionality that suits the needs of your application is present
in the framework, you don't have to worry about that
aspect of the application. This, in turn, frees up developers to
focus on the core application rather than the infrastructure.This is not a perfect analogy, but the point is that a good framework
should provide much of the infrastructurethe foundation and
the plumbing, for example. The most important aspect of a framework,
however, is that it should provide extension points throughout.Framework extension points, also referred to as
"hooks," allow you to extend the
framework in specific places to adapt it to meet the
application's requirements. Where and how a
framework provides these hooks is very important. If
they're provided incorrectly or in the wrong
locations, it becomes very hard for an application to adapt the
framework, which makes the framework less useful. If you extend the
framework in places where there are no extensions points or in ways
that the framework authors never intended, upgrading the application
to newer versions of the framework becomes problematic. The rest of
this chapter focuses on where the Struts framework provides these
extension points and how you can take advantage of them to build out
specialized functionality for your application. |
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