[Cayenne-dev] Re: Cayenne under OSGi

Oh and if anyone thinks this is controversial for any reason, please comment.

A.

Just committed configs needed to turn cayenne-di.jar and cayenne-server.jar into proper OSGi bundles. I used the default configuration of maven-bundle-plugin, so every single Cayenne package is exported in the bundle. In the future we may be more specific. cayenne-di.jar has no dependencies. cayenne-server.jar has a bunch of optional dependencies, and 4 required ones:

cayenne-di
commons-collections
commons-logging
velocity

Also to generate a proper OSGi version (3.2.0.M2-SNAPSHOT) I had to add a dot to our Maven versioning scheme, so the trunk is now called 3.2.M2-SNAPSHOT. Which was probably the right thing to do anyways.
Still TODO.

Andrus

After today’s round of changes (CAY-1886), I am able to start Cayenne bundles in an OSGi container (Felix). Here are the prerequisites (shown as “install” commands inside the Felix container). As you see we can’t use some of the direct dependencies of Cayenne, specifically commons-logging and velocity, in an OSGi container. However there are suitable replacements out there:

install file:/Users/cayenne/.m2/repository/commons-collections/commons-collections/3.2.1/commons-collections-3.2.1.jar
install file:/Users/cayenne/.m2/repository/org/slf4j/jcl-over-slf4j/1.7.5/jcl-over-slf4j-1.7.5.jar
install file:/Users/cayenne/.m2/repository/org/slf4j/slf4j-api/1.7.5/slf4j-api-1.7.5.jar
install file:/Users/cayenne/.m2/repository/org/slf4j/slf4j-simple/1.7.5/slf4j-simple-1.7.5.jar
install file:/Users/cayenne/.m2/repository//org/apache/servicemix/bundles/org.apache.servicemix.bundles.velocity/1.7_6/org.apache.servicemix.bundles.velocity-1.7_6.jar
install file:/Users/cayenne/.m2/repository/commons-lang/commons-lang/2.4/commons-lang-2.4.jar

... now finally install 2 Cayenne bundles ...

install file:/Users/cayenne/work/cayenne/cayenne-di/target/cayenne-di-3.2.M2-SNAPSHOT.jar
install file:/Users/cayenne/work/cayenne/cayenne-server/target/cayenne-server-3.2.M2-SNAPSHOT.jar

after that cayenne-server can be started, and I end up with the following container state:

g! lb
START LEVEL 1
    ID|State |Level|Name
     0|Active | 0|System Bundle (4.2.1)
     1|Active | 1|Apache Felix Bundle Repository (1.6.6)
     2|Active | 1|Apache Felix Gogo Command (0.12.0)
     3|Active | 1|Apache Felix Gogo Runtime (0.10.0)
     4|Active | 1|Apache Felix Gogo Shell (0.10.0)
    16|Resolved | 1|Commons Collections (3.2.1)
    23|Resolved | 1|jcl-over-slf4j (1.7.5)
    24|Resolved | 1|slf4j-api (1.7.5)
    25|Resolved | 1|slf4j-simple (1.7.5)
    27|Resolved | 1|Cayenne Dependency Injection Container (3.2.0.M2-SNAPSHOT)
    31|Resolved | 1|Apache ServiceMix :: Bundles :: velocity (1.7.0.6)
    32|Active | 1|Cayenne Server (3.2.0.M2-SNAPSHOT)
    35|Resolved | 1|Commons Lang (2.4.0)

Next step is to write a bundle that uses Cayenne and see what we need to do with the ClassLoader.

A.

Hi All,

Great job Andrus!!

For the next step you were talking about, I think we can use this example:
http://www.snip2code.com/Snippet/12372/Use-Apache-Cayenne-under-OSGi-environmen
where you can see an example of a bundle activator.

Hope this can help in the following steps...

Bye
cghersi


2013/11/20 Andrus Adamchik <andrus@objectstyle.org>

So this is done. Cristiano, appreciate if you could try it in your environment. An example of how to use Cayenne with OSGi is available on GitHub [1]. Here is how you bootstrap it in your own module:

   Module osgiModule = OsgiModuleBuilder.forProject(Activator.class).withDriver(Driver.class).module();
   return new ServerRuntime("cayenne-osgi-example.xml", osgiModule);

As you see, no need to enumerate your classes. Also I suspect instead of binding the driver, in a real OSGi environment Cayenne stack will need to refer to some OSGi service that encapsulates the DataSource. We can provide integrations for that too. And don’t forget to stop it when you your bundle is stopped, as you don’t want to keep Cayenne threads and other resources hanging around, eventually killing your container:

   cayenneRuntime.shutdown();

Cheers,
Andrus


[1] https://github.com/andrus/cayenne-osgi-example

Hi Andrus, great job!

I have to say that we always used it under Equinox implementation, so
perhaps in Felix seems to be simpler.

Just two notes on our experience under OSGi that may help to overcome
eventual problems of class/resource loading.
1) OSGi load of resources like xml config file: this sometimes is tricky
under OSGi. We solved our problems creating another bundle as a fragment
host of cayenne-osgi bundle, where we place the **.map.xml, the
cayenne-MyDomain.xml and (optionally) the dbcp.properties (as we use
org.apache.commons.dbcp for pooled connections).
2) Class loading: if your bundle expose some methods to interact with DB,
the lazy load of the classes inside OSGi environment may bring you some
headache, as you cannot be sure on the order of class loading among the
different bundles (this is why we provided the ClassRegistry and force the
load of such classes in the start() of the bundle: to be sure that such
classes are correctly loaded from the correct bundle when we want!). This
strange behavior was discovered after one year that we were using Cayenne
under OSGi! So, perhaps, the fact that now with the test bundle Andrus
provided everything seems working can be misleading. But I cannot prove my
sentence as this is a bug very difficult to reproduce.

So, at the end, the implementation of Andrus seems effective and works well
for me, but the test of someone else may give us more feeling about the
resolution of the issue.

Bye
cghersi


2013/11/24 Andrus Adamchik <andrus@objectstyle.org>