A story of migrating a Java application to Equinox and OSGi

Bill Kayser has written an interesting summary of his experience migrating a 600,000 line multi-tier swing based application to run on Equinox. He begins the story with a very good explanation of OSGi as the platform for applications with a service oriented architecture.

It is interesting to see the benefits Bill achieved as the result of migrating to Equinox.

The improvements included but were not limited to:

  • Going from 25,000 lines of ant code required for a full build down to about 200 lines of boilerplate configuration, plus about 200 lines of custom callbacks,
  • We eliminated about seventy class file catalogs used to ensure extra classes were not inadvertently shipped in the wrong jar file or duplicated unnecessarily,
  • Reducing the size of application distros by eliminating unused dependencies
  • Surfacing previously unknown bugs based on dangling references to missing classes and libraries,
  • Eliminating a large body of code devoted to managing extensions with segregated class spaces using custom class loaders.
  • Going from managing four different runtime configurations for each application–the IDE classpaths, the IDE launchers, the runtime script classpaths, the build script classpaths–down to a single feature descriptor listing the OSGi bundles comprised by each application.

And probably the biggest improvement was in the introduction of the extension mechanism provided in Equinox to extend applications with a sort of dependency injection. This allowed us a new lease on life as a platform for custom configuration and specialized implementations instead of a product trying to be all things to all customers.

Well worth the read!