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The OSGi (http://www.osgi.org/) framework is a powerful Java tool providing component based service and dependency management. OSGi components can be remotely installed, started, stopped, updated and uninstalled without shutting down your application. Also, OSGi provides far greater dependency management than the basic Java classpath mechanism, allowing you to specify specific versions of dependencies and keep dependencies private so that other components cannot load them. One of the most notable usages of OSGi is the Eclipse Plugin Container. A good starting point for more information is the Wikipedia page http://en.wikipedia.org/wiki/OSGi and the Further Reading section of this document.

1. Loading Groovy as an OSGi service
The Groovy jar files are released with correct OSGi metadata, so they can be loaded into any OSGi compliant container, such as Eclipse Equinox or Apache Felix. The metadata can be viewed by looking at the jar file's MANIFEST.MF file. For instance, your Jar manifest might contain these lines:
 

This declares to the OSGi container that the Jar is version 1.7.0 and provides the specified packages for import by other components.

The following examples all use the Eclipse Equinox container, which can be downloaded from the Internet or found in an Eclipse installation.

Perform the following steps to install and start the Groovy Jar in an OSGi container:

Start the OSGi container in console mode:

This should bring up an OSGi console prompt:

You can see the system status of the container at any time using the "ss" command.

Install the Groovy jar file using "install" and a file URL to your groovy-all jar:

The container will assign the bundle an identifier. Start the bundle using the "start" command:

Verify the bundle is started using "ss":

You can list all the packages the Groovy bundle provides with the "packages" command:

   

2. Hello World groovy bundle that loads groovy-all .jar into OSGi container.

3. Hello World groovy bundle that includes groovy-all in classpath

4. Publishing a service written in Groovy

5. Consuming a service (the groovy-ness of which is immaterial)

Further Reading
Sunil Patil wrote a 3 part writeup with full code listings on JavaWorld. Part 1 details the basics os a Hello World service. Part 2 describes the Spring DM product and adding Spring to OSGi. And Part 3 covers several web deployment scenarios and issues. Also, Joseph Ottinger h http://www.javaworld.com/javaworld/jw-03-2008/jw-03-osgi1.html http://www.javaworld.com/javaworld/jw-04-2008/jw-04-osgi2.html http://www.javaworld.com/javaworld/jw-06-2008/jw-06-osgi3.html http://www.theserverside.com/tt/articles/article.tss?l=OSGiforBeginners http://hamletdarcy.blogspot.com/2008/12/beginners-guide-to-osgi-on-desktop.html

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