Mastering modularity - OSGi in Action - page 68

2.9 Summary

We've covered a lot of ground in this chapter. Some of the highlights include the
following:

Modularity is a form of separation of concerns that provides both logical and
physical encapsulation of classes.

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Modularity is desirable because it allows you to break applications into logically
independent pieces that can be independently changed and reasoned about.

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Bundle is the name for a module in OSG i. It's a JAR file containing code,
resources, and modularity metadata.

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Modularity metadata details human-readable information, bundle identifica-
tion, and code visibility.

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Bundle code visibility is composed of an internal class path, exported packages,
and imported packages, which differs significantly from the global type assump-
tion of standard JAR files.

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The OSG i framework uses the metadata about imported and exported packages
to automatically resolve bundle dependencies and ensure type consistency
before a bundle can be used.

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Imported and exported packages capture inter-bundle package dependencies,
but uses constraints are necessary to capture intra-bundle package dependen-
cies to ensure complete type consistency.

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From here, we'll move on to the lifecycle layer, where we enter execution time aspects
of OSG i modularity. This chapter was all about describing bundles to the OSG i frame-
work; the lifecycle layer is all about using bundles and the facilities provided by the
OSG i framework at execution time.