Question

I plan to deploy an EAR packaged application into JBoss v4.2 as a folder containing the content of the EAR. Until now the EAR is deployed as a single file. I hope to be able to replace single JARs without the need to restart the application.

Is there any kind of event listener or annotation that can be used to register those JAR files upon deployment? The idea is a plugin like deployment of some features implementing a known interface. The plugins shall be used in a Seam webapp environment and may be exchanged with updated versions on the fly.

Any ideas? Thanks.

Answer 1

AFAIK, this is not possible/supported. When using an exploded EAR, touching an individual module would trigger the hot deployment of the whole EAR.

From Lightweight Java Web Application Development: Leveraging EJB3, JSF, POJO, and Seam:

3.4.2. Hot Deployment

Another JBoss feature that helps agile
development is exploded archives. The
EAR, EJB3 JAR and WAR files are not
necessarily JAR files in the JBoss
container. They can be directories
containing the contents of the JAR
file. For instance, instead of
deploying the dvdcatalog.ear file as a
single file, you can deploy it as
directory.

With the exploded directories, you can
make changes to any single JSP page or
Java class file in the application
while the server is running. Then you
can touch the META-INF/application.xml
file in the exploded directory (i.e.,
update the file’s timestamp to
current) to re-deploy the entire EAR
application. This further saves
significant amount of time for rapid
turn-around agile developers.

What you’re looking for doesn’t sound simple. It would require detecting the change, unloading loaded class definitions coming from that JAR (assuming this information is known), reloading classes (something like that but I’m pretty sure I’m oversimplifying). Maybe more a job for an OSGI server.

See also

• JBossClassLoadingUseCases
• ClassLoadingConfiguration