Paris JUG – OSGI conference
21 October, 2008 (22:38) | Paris JUG, event, java | By: fabien
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A couple of weeks ago, I discovered Paris JUG, a java user group based on Paris area. As they were giving a free OSGI conference, subject which interest me, I went there last tuesday.
Here are various notes I have taken there :
Incoming events in the group :
- February 2009 : It’s the first birthday of the group. On this occasion, there will have quickies (15 minutes presentations)
- Call for blogger (I have asked to add my blog and I am waiting the answer)
- 4 November : conference on GWT (I intent to come)
- 12 November : Open source exchange
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Without OSGI
- It’s possible to avoid collisions between different versions of the same library by repackaging them (changing package names) : It’s was has been done with tomcat which includes its own version of commons-dbcp (see reference)
Comparison of OSGI and JCP:
- To become a member :
- TCK (conformity tests) :
- JCP : accessible especially to the open source community
- OSGI : less easily accessible
OSGI and the JSR :
- JSR 291 : created by the OSGI community to integrate in JAVA SE a dynamic component model based on OSGI
- JSR 277 : has for goal to integrate the notion of modules in JAVA. This might not succeed and be merged with JSR 291
- Spring DM (Dynamic Modules)
- will probably become the next OSGI standard because it seems to be welcomed by the JAVA community
- is normalizing its main ideas with the RFC 124. It seems to threaten the notion of «declarative service » (OSGI v4), which is a layer on top of OSGI targeting the declaration of imported and exported services by the bundle.
OSGI and the java applications :
- Apache geronimo : the jars are OSGIfied but are not inside an OSGI container
- Apache felix
- implementation of an OSGI container by the apache community
- allows to generate OSGI manifests with Maven
- eclipse : based on OSGI since version 3.0
- equinoxe : implementation of an OSGI container for eclipse
- eclipse RAP (Rich Ajax Platform) : equinoxe in a web application
- eclipse BIRT : example of a web application with its own OSGI container
- Websphere 6.1 : full OSGI. It doesn’t expose OSGI APIs to web applications.
- Service Mix, an ESB (Enterprise Service Bus) : manages (among others) the autorefresh of added/removed OSGI services.
- PAX : open source project wrapping third party libraries with OSGI format. It’s compound of (among others) :
- JUnit : it’s mono ClassLoader and that’s a problem with OSGI
- Spring DM : probably the future OSGI standard
Remarks on OSGI :
- One ClassLoader per bundle
- Class.forName : to avoid with OSGI as much as possible. See the discussion on that subject.
- The OSGI ServiceTracker can see many service (JAVA interface) implementations
- Problem : How to add a dynamic dependency ? Solution: attach a « bundle fragment » by adding « Bundle-Host: bundle_name» in the manifest
Various notes :
- The manifest file is limited to 76 columns (strange limit …)
- Eclipse feature : it’s a set of plugins, for example a functional domain in an enterprise application
To learn more :
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