[jboss-as7-dev] NoClassDefFoundError

[Jason T. Greene]

On 12/7/11 3:35 PM, Bill Burke wrote:
> This is what I don't like about AS7.  While every other JBoss version
> was include everything, AS7 is exclude everything by default and you
> must be explicit.
>
> Wouldn't the general case be to include everything, with exclude being
> the minor case?

Yes there are drawbacks but it's worth it (IMO). As we saw in the past, 
including everything leads to "surprises" and slower classloading. An 
opt out model has the sames problems because you are still vulnerable to 
pulling in stuff you never intended. An app server update can readily 
conflict with your deployments and/or modules. So you spend little time 
up front, and potentially a lot of time later on down the road trying to 
fix conflicts. An opt-in model though you spend a little more time up 
front AND it makes you actually THINK about your dependencies, but your 
chances of conflicts down the road become very slim.

There is of course some balance to be had, so in the case of EE 
deployments we try to add a set of sensible imports (which can still be 
opted out of). The goal is that a user only sucks in our supported APIs 
and not whatever random thing we used to implement them. If however you 
work with pure modules, as in this http client case, then you don't get 
this particular feature (as doing it reuires understanding what the 
module actually does, something known to us when its an EE deployment). 
Of course they could have just added the http client jar to their 
deployment, or they could have made it a global module, or used 
class-path to an extrenal ref, or used extension-list. All of which 
would get an SE sdk import.

What would make initial generation of modules easier, for those that 
choose to use them, is if we had more tooling (contributions welcome 
anyone who is listening). For example something that takes a maven dep 
list and constructs a potential module definition.

One last thing to add is that Java SE itself is moving to an opt-in 
model (Java modules). So really the days of the big-ball-of-mud approach 
are numbered, or as Mark Reinhold put it "the classpath is dead".

-- 
Jason T. Greene
JBoss AS Lead / EAP Platform Architect
JBoss, a division of Red Hat