Universal Middleware: What's Happening With OSGi and Why You Should Care

The Open Services Gateway Initiative (OSGi) Alliance is working to
realize the vision of a "universal middleware" that will address issues
such as application packaging, versioning, deployment, publication,
and discovery. In this article we'll examine the need for the kind of
container model provided by the OSGi, outline the capabilities it would
provide, and discuss its relationship to complementary technologies
such as SOA, SCA, and Spring. Enterprise software is often composed of
large amounts of complex interdependent logic that makes it hard to
adapt readily to changes in requirements from the business. You can
enable this kind of agility by following a Service Oriented Architecture
(SOA) pattern that refactors a system into application modules grouped
by business functions that expose their public functionality as services
(interfaces)... we'll explain how an Open Services Gateway initiative
(OSGi) container would solve them. We'll begin with an introduction
to the OSGi's solution to the problem, concepts, and platform, and
then we'll delve into the evolution of the OSGi from its past in the
world of embedded devices to its future in enterprise systems. We'll
also explain the relationship between the OSGi and other initiatives,
containers, and technologies to provide a comprehensive picture of
the OSGi from the perspective of software development... Conceptually
both SCA and OSGi provide a composite model for assembling a
services-based composite application that can expose some services
to the external world as well as invoke external services. In OSGi
R4, declarative services define a model to declare a component in
XML, capturing its implementation and references. Besides SCA-like
component-level information, the OSGi model captures additional
information to control runtime behavior. For example, R4 provides
bind/unbind methods to track the lifecycle or manage target services
dynamically. SCA metadata defines wires between components or from a
component to a reference in its composite model...