[jboss-as7-dev] IMPORTANT TCCL & JAXP Changes!

[Jaikiran Pai]

On Monday 29 August 2011 08:32 PM, Jason T. Greene wrote:
> Hello Everyone,
>
> While we still want to avoid using TCCL for anything but interacting
> with thirdparty components or the SDK [1], there are some changes that
> have been made to the current master that make it easier to work with.
>
> To discourage use in AS, and prevent the wrong classloader from ever
> being used, in many contexts (e.g. service lifeycle methods) we used to
> null the TCCL. Unfortunately due to (yet another) bug in various JAXP
> API implementations, a null TCCL, would trigger this problem:
> https://issues.jboss.org/browse/AS7-1630
>
> It also made using JAXP from a service or a management operation a
> little unwieldy since you had to push/pop TCCL yourself, as decribed in [1].
>
> To address these issues we now ALWAYS set TCCL to the defining
> classloader of the component in the following cases:
>
> - MSC Service lifecycle (start, stop)
> - Listener callbacks
> - MSC Lifecycle Context Execution Tasks
> - Operation Handler invocations (includes all subsystem logic)

Does this also include DUPs which trigger the component class 
instantiation? Last time I checked [1], there was an issue where a DUP 
would trigger a class load of a user class, leading to the static block 
of that user class being run and if that static block used JAXP API, it 
would run into trouble due to null TCCL.

[1] http://lists.jboss.org/pipermail/jboss-as7-dev/2011-July/003337.html

-Jaikiran
>
> What does this mean to you?
>
> 1. If you are writing code that is executing in a service or as part of
> your subsystem you no longer need to worry about setting the TCCL, it
> will be set to your module classloader for you. You can therefore use
> JAXP or any other service loader style framework without worrying about
> this.
>
> 2. If you are writing code that is executed on behalf of an EE request,
> then TCCL will STILL point to the spec required deployment classloader.
> You MUST still push/pop the TCCL as described in [1] when using JAXP or
> any other service loader framework.
>
> If you have any questions about this, feel free to ping me about it.
>
> [1] http://community.jboss.org/wiki/ModuleCompatibleClassloadingGuide