Tuesday, February 22, 2011

Out with the old (SPI) - Modular Java with OSGi

Renewal starts with death. For me renewal often manifests itself in form of a real or imagined virus detection on my laptop. It prompts me to delete large swaths of stuff and replace it with new things. The latest outbreak was FakeJava. So I promptly deleted my old faithful JDK/JRE and Eclipse and anywhere else in the system where Java installers were lurking. For a Java developer this is pretty drastic. It gave me the chance to update my Eclipse with Helios and try the new improved osgi container implementation lurking in the Eclipse plugins folder. If you are a Java developer of any calibre and not fatally attracted to vim and emacs, you probably have Eclipse installed (or had it at some stage). Anyway long story short - dig inside the Helios install and you shall see something along the lines of org.eclipse.osgi_3.6.1.XXX.jar. This is the source of all Eclipse plugin goodness (no it is not all beacuse of the SWT).

Start up this jar as the osgi container, java -jar org.eclipse.osgi_3.6.1.XXX.jar -console will start up in interactive mode. If you are into IDE tooling (that is the reason you are using Eclipse in the first place anyway) there are a couple of options to make osgi play nicely with you - Eclipse PDE or BndTools. I have written up a few brief steps based on my experience getting a non-SWT, osgi-bundles based WorldWind GUI going. The basic ingredients were already there:

1) Eclipse PDE Tutorial to wrap Jogl (based on Jogamp but works just as well with classic JOGL).
2) Shrink-wrapped Eclipse projects to use with WorldWind, including Jogl and SWTGLCanvas (which I did not quite get to run).
3) BndTools component based development, somehow similar to fragments.
4) Using Eclipse Bundle Repository plugin to pull in the PDE based bundles - exported out of eclipse using Export Application Wizard (+some platform specific forcing hackery). Add this to build.bnd in the bndtools main repo - bndtools.bndplugins.repo.eclipse.EclipseRepo;location=${worldwind-repo};name=WorldWind-repo and the freshly exported PDE bundles will become available to BndTool. This step was the most frustrating and probably would not really need to be done if you stick with pure PDE or pure BndTools, but I had a lot of fun mixing and matching.
5) After everything is set-up you can create a project along the lines of the component tutorial using IGlobe instead of IGreeting and get WorldWind to provide you with a JPanel.
6) BndTools does not add the contents of Jar-in-jar bundles PDE produces into buildpath, make sure you add worldwind.jar and Jogl into the path for a sample build. At runtime OSGi will take care of this.

After this all the bundles will be playing happily in the OSGi Framework, things will look something like this:


START LEVEL 1
   ID   State         Level  Name
[   0] [Active     ] [    0] OSGi System Bundle (3.6.1.R36x_v20100806)
[   1] [Active     ] [    1] org.trikend.glob3.globeui (0)
[   2] [Active     ] [    1] Apache Felix Shell Service (1.4.2)
[   3] [Active     ] [    1] Apache Felix Declarative Services (1.4.0)
[   4] [Installed  ] [    1] JOGL native bindings for Linux x86 (1.1.2)
[   5] [Active     ] [    1] org.trikend.glob3.globe-impl (0)
[   6] [Active     ] [    1] JOGL (1.1.2)
[   7] [Active     ] [    1] osgi.cmpn (4.2.1.201001051203)
[   8] [Active     ] [    1] org.trikend.glob3.api (0)
[   9] [Installed  ] [    1] JOGL native bindings for MacOSX (1.1.2)
[  10] [Active     ] [    1] Worldwind (1.0.0)
[  11] [Resolved   ] [    1] JOGL native bindings for Windows x86 (1.1.2)
[  12] [Active     ] [    1] Apache Felix Shell TUI (1.4.1)


Here is a screenshot for further clarity (or lack thereof).

worldwind_bndtools_less
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