[rules-users] NullPointerException with Wrapper objects

[Wolfgang Laun]

All right, let's hope that "business user" is up to write the rules, even
without null checks ;-)
Seriously now: are they up to handling monetary units represented as
floating point numbers? A recent thread has emphasized the problems arising
from tests such as floatVal <= floatConst, and I've been preaching about
possible inconsistencies due to the inherent nature of FP arithmetic, even
for doing sums. BigDecimal is one solution, but I guess your BUs will go
ballistic if you tell them about the consequences...

But here's my last proposal for circumnavigating the NPE issue:

At the point of fact insertion, wrap all "dangerous" bean objects into a
container fact with a single field and insert the container. Write rules
matching the container, testing the wrapped object for field == null and
whatever; if so, change and log; and now insert the wrapped object as a fact
proper. (If necessary, you could even write a single rule for all fact
types, using inspection to determine all dangerous fields.)

-W


2009/5/14 Shabbir Dhari <sdhari at hotmail.com>

>  Thanks to all.
>
> The problem we have is that rules will be code by business user. As a
> developer I don’t mind putting null check on every rule. But for business
> user its unacceptable for checking null for the same attribute in around 50
> rules.
>
> Shannon, can you please elaborate more about your solution or if possible
> post some simple code?**
> > Date: Wed, 13 May 2009 08:28:53 -0700
> > From: greg_barton at yahoo.com
> > Subject: RE: [rules-users] NullPointerException with Wrapper objects
> > To: rules-users at lists.jboss.org
> >
> >
> > Well, like Wolfgang said, good luck with that. :) The only rules engine I
> know that does this is Tibco BusinessEvents, and it's accomplished by making
> a copy of your objects before inserting them into working memory.
> >
> > >From this forum post I'm guessing JRules doesn't do it:
> http://forums.ilog.com/brms/index.php?topic=1439.0
> >
> > And probably Blaze Advisor doesn't do it either:
> >
> http://discuss.fico.com/blaze/board/message?board.id=Blaze_Advisor_Users_Forum&message.id=591
> >
> > So, I'm thinking you're stuck with having to do null checks.
> >
>
>
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