[equinox-dev] Bundle services

["Walter Harley" <wharley@xxxxxxx>]

In Java 1.6 (and to some extent earlier versions) there is a mechanism
to allow a jar file to declare that it contains an implementation of
some standard service interface, and to discover and load service
implementations.  The basic mechanism is that the jar file contains a
folder named META-INF/services, within which there are text files named
after interfaces; within each text file are the qualified names of
classes that implement the interface.  There is then a utility
java.util.ServiceLoader, which takes a classloader and the Class object
of an interface, and returns an iterator of implementations.

In Eclipse, the way that I know to publish services is that one plug-in
declares an extension point and an interface, and other plug-ins extend
the extension point and declare the names of the implementation classes;
IConfigurationElement.createExecutableExtension() is then used to load
the implementations.  But this mechanism has the disadvantage that it is
not standardized across different services - that is, I can't easily
write an arbitrary "ServiceLoader" for plug-ins, because the extension
points corresponding to different services do not share the same schema.

I have just discovered the org.osgi.framework.ServiceFactory,
ServiceRegistration, etc. interfaces.  Are these intended to provide a
standardized service-provider system for OSGi?  If so, is there
somewhere I can read more about these, beyond the javadoc for the
classes themselves?  Or if the javadoc is all that exists, is there a
particular class I should start with?

Or, are these interfaces meant for lower-level functionality, or some
such, so I should continue to use extension points?

  ***

My application, in case anyone's interested, is Java 6 annotation
processing.  Annotation processors are third-party components that
execute at compile time to report errors and generate additional
resources.  They plug into Sun's javac by using the Java service
provider mechanism; I'm trying to perform the equivalent for processors
written as Eclipse plug-ins as well as jar files.

Thanks,
  -Walter Harley
   JDT APT team
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