[jboss-dev-forums] [Design of JBoss jBPM] - how crucial are exception handlers ?

[tom.baeyens@jboss.com]

i'm in doubt about the importance of exception handlers in the PVM.  i want your opinion on whether they should go in the PVM.

exception handlers are only to catch java exceptions that occur in user code (delegation classes).  The purpose of exception handlers is to create global catch clauses that handle certain exceptions for multiple invocations of user code.  This way, the try-catch doesn't have to be programmed into each user-code-class individually.

users could create abstract base classes to include the handling of exceptions and handle it that way.  but that would not give the flexibility of the parent lookup of exception handlers.  (i'm in doubt if that is needed)

also, if we do it on the level of the pvm, exception handlers don't make a distinction between process language code and real user code in case of jPDL.  the node behaviour implementation is considered a delegation class and hence guarded with the exception handler.  but for the exceptions that are thrown, the pvm doesn't know if it comes from the process language implementation or from real user code.

an alternative could be interceptors.  i have in jPDL a mechanism for installing an interceptor for user code.  i could do something like that in the PVM as well.  that could be an alternative way to enable exception handling functionality to clients of the pvm.    the question there would be: what levels would we support interceptors: in jpdl now, it is a static member field, so it's only on the level of the complete engine.  But we could also support it on process definition, delegation or even on execution instance level.

those are my thought pieces that don't come to conclusion.  your thoughts are appreciated.

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