[jboss-dev] Classloading and partial deployments

[Adrian Brock]

On Fri, 2008-10-17 at 11:06 +0200, Mladen Turk wrote:
> Hi,
> 
> Have some weired idea and would like to hear if someone
> already faced something similar.
> 
> It's not directly related neither to AS nor Tomcat
> but both of them have the conceptually similar application
> classloaders where you put some component .jar in
> some (usually) lib/ folder and it gets loaded and
> hopefully unloaded on undeployment.
> 
> Now, the handy feature I need would be similar to Operating
> System "Move on reboot" or "Reboot required" functionality.
> 
> In essence, like with some native installations there are two
> major issues. Depending on what you are installing it might
> just go on, or it might require OS reboot. Installation might
> just be done for current user or it might require elevated
> security.
> 
> So the first thing, if for example, my .war or .ear needs to
> install something to core AS or to the catalina.home/ext
> is the option to tell the deployer to unpack something in
> a different location, and mark the "OS" (in this case my
> container) to reboot. This requires delegating this
> to the parent classloader or even to the
> sun.misc.Launcher$ExtClassLoader
> 
> The second thing is undeployment or uninstall where some
> part of what was installed can be physically deleted only on
> reboot (probably either by some cleanup task on shutdown or
> by some cleanup on startup)
> 
> This probably breaks a whole bunch of specs and has potential
> security implications, but given "admin" security credentials
> it can be done without impacting "user" security.
> 
> Dunno how Adrian did it for MC, but I suppose it just
> sweeps trough some given .jar list on deployment and loads
> those classes.
> 

You can do this already in JBoss5 for those classes that are hot
deployed, provided you use the OSGi classloading rules.

The classloading depenencies will automatically cause
the importing applications to be redeployed when a 
dependent jar changes.

But these classloading dependencies are not currently
specified by our services (see an earlier post of mine
on this list).

If the classes are not hotdeployed, e.g. 
the jars in JBOSS_HOME/lib then you have to reboot the whole
server.
-- 
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Adrian Brock
Chief Scientist
JBoss, a division of Red Hat
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