RE: OSWorkflow: new Exception handling

Speaking of exception handling...

Josh Bloch's book "Effective Java" provides a couple of 
good rules of thumb for exception handling.

{{

Item 40:  Use checked exceptions for recoverable conditions
          and run-time exceptions for programming errors


  	"To summarize, use checked exceptions for recoverable
	 conditions [...] If you believe a condition is likely
       to allow for recovery, use a checked exception; if not,
       use a run-time exception."


Item 41:  Avoid unnecessary use of checked exceptions

Item 43: Throw exceptions appropriate to the abstraction

}}

I highly recommend "Effective Java".

-Sean



> -----Original Message-----
> From: Nick Dellamaggiore 
> 
> Good job on releasing 2.5!  I can finally release my code into production
> know its backed by a production quality Workflow solution.
> 
> <<on soapbox>>
> One thing I immediately noticed upon upgrading (I'd been using a 2.5
> snapshot) was the changes in exception handling.  It seems like EVERYTHING
> in Workflow throws a WorkflowException now. Furthermore, most the
> implementing methods in AbstractWorkflow throw an additional
> StoreException!
> If you're going to throw both exceptions, you should declare them in the
> throws clause of the interface, not the implementation.
> 
> My general philosophy on exception handling is if the end user of an API
> didn't do anything wrong (like pass null parameters, use invalid SQL
> syntax,
> etc) and there are no exceptional circumstances that could come into play
> (service not running on remote computer, etc), then the end user shouldn't
> have to catch non-RuntimeExceptions.
> 
> For example, Workflow.getCurrentSteps(long id) throws StoreException.
> Now,
> why should the end user of the API care if the underlying workflow store
> blows up while accessing the database (or whatever the backing store
> uses)?
> If the store blew up, then the person who implemented that store needs to
> go
> fix it. Fire up JIRA and create a new issue.  The end user just wants to
> getCurrentSteps. If there are no current steps, then an empty List should
> be
> returned (or null, its up to the developer).
> 
> Now, if the database itself was down entirely or the connection parameters
> are wrong, its not the Store implementors fault. But if this was the case,
> catching the StoreException would be pointless as the entire application
> would be hosed anyways (no db). So for this special case, it would be
> better
> to throw a RuntimeException that would bubble up to the view layer.
> 
> Finally, if WorkflowStore is going to throw StoreExceptions, the reason
> for
> the throw should be declared in the javadocs. I'm assuming WorkflowStore
> would throw a StoreException if there was an error querying/persisting
> workflow steps.  Personally, I wouldn't have WorkflowStore throw anything.
> But, if it must, I think AbstractWorkflow should catch those Exceptions
> and
> log them or something. I mean, as an end user, what should I do if I get a
> StoreException? Log it? There really is no means of recovery if the
> WorkflowStore itself is blowing chunks.
> 
> What do you guys think? Maybe I'm totally missing something here.  Could
> you
> please explain the rationale behind OSWorkflow's new Exception handling
> (or
> lack thereof)?  Please don't take the post personally. I'm really anal
> about
> Exception handling and the new version pushed a few buttons =)  ...good
> thing Eclipse has a "surround with try/catch" fix button!
> <<off soapbox>>
> 
> Thanks for all the hard work!
> -nick dellamaggiore
> 
> 
> 
> 
> 
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