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There is no way you can recover from an exception on the LHS, so that
makes me reluctant to allow users to create something that swallows
exceptions. If you worried about it, put a try catch around the inserts.<br>
<br>
Mark<br>
Yang Song wrote:
<blockquote
cite="mid:657190290708242115r2d62cdbfn11e66d432a2742f4@mail.gmail.com"
type="cite">
<p>Mark, Michael, Edson and all,</p>
<div>Thanks very much for participating into this discussion. I am so
glad to see that the response has quickly been turned out into an
output. Really appreciate your help, Mark. </div>
<div> </div>
<div>Sorry may be a liittle too aggressive, but here comes another
thought of mine: if we can have the RHS to have exception handler, why
not the LHS has exception handler too? This is sometimes very helpful
when someone abuses eval() in LHS.
</div>
<div> </div>
<div>Best Regards,</div>
<div>Yang</div>
<div><br>
</div>
<div><span class="gmail_quote">On 8/25/07, <b
class="gmail_sendername">Mark Proctor</b> <<a moz-do-not-send="true"
href="mailto:mproctor@codehaus.org">mproctor@codehaus.org</a>>
wrote:</span>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;">
<div text="#000000" bgcolor="#ffffff">Here is the unit test showing
how it works, this uses the programmatic api, you can also use the
drools.consequenceExceptionHandler property. This will be in the 4.0.1
release, which is out this monday.
<br>
<a moz-do-not-send="true"
onclick="return top.js.OpenExtLink(window,event,this)"
href="http://jira.jboss.org/jira/browse/JBRULES-1123" target="_blank">http://jira.jboss.org/jira/browse/JBRULES-1123</a><br>
<br>
public void testCustomConsequenceException() throws Exception
{ <br>
final PackageBuilder builder = new PackageBuilder();<br>
builder.addPackageFromDrl( new InputStreamReader(
getClass().getResourceAsStream( "test_ConsequenceException.drl" ) ) );<br>
final Package pkg = builder.getPackage();<br>
<br>
RuleBaseConfiguration conf = new RuleBaseConfiguration();<br>
CustomConsequenceExceptionHandler handler = new
CustomConsequenceExceptionHandler();<br>
conf.setConsequenceExceptionHandler
( handler );<br>
<br>
final RuleBase ruleBase = getRuleBase(conf);<br>
ruleBase.addPackage( pkg );<br>
final WorkingMemory workingMemory =
ruleBase.newStatefulSession();<br>
<br>
final Cheese brie = new Cheese( "brie",
<br>
12 );<br>
workingMemory.insert( brie );<br>
<br>
workingMemory.fireAllRules();<br>
<br>
assertTrue( handler.isCalled() );<br>
}<br>
<br>
public static class CustomConsequenceExceptionHandler implements
ConsequenceExceptionHandler {
<br>
<br>
private boolean called;<br>
<br>
public void handleException(Activation activation,<br>
WorkingMemory workingMemory,<br>
Exception exception) {
<br>
this.called = true; <br>
}<br>
<br>
public boolean isCalled() {<br>
return this.called;<br>
} <br>
}<br>
<span class="sg"><br>
Mark</span>
<div><span class="e" id="q_1149a7514ab8743e_2"><br>
Mark Proctor wrote:
<blockquote type="cite">ok I have added a
ConsequenceExceptionHandler to RuleBaseConfiguration, default just
wraps and re-throws as a runtime exception. You can override this to
provide a custom consequence exception handler. But do be aware that if
you swallow the working memory integrity may be invalid, if the error
happened during a working memory action.
<br>
<br>
Mark<br>
Anstis, Michael (M.) wrote:
<blockquote type="cite">
<div dir="ltr" align="left"><span><font color="#0000ff"
face="Arial" size="2">For what it's worth I think this would be a good
idea too.</font></span></div>
<div dir="ltr" align="left"><span></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff"
face="Arial" size="2">Perhaps the default ASM wrapper around the RHS
could use a try...catch block and log any exceptions of a rules'
activation in a (drools) accessible log? Heck you could even allow
certain accepted exceptions to be defined as a property of the rule;
and any other non-defined exception types cause the session to become
invalidated. If we're ever to let "the business" define rules we need
to accept they might make mistakes that we're better off capturing and
report back than invalidate the whole session. </font></span><span><font
color="#0000ff" face="Arial" size="2">Why should a whole session be
invalidated because a single rule activation failed anyway?</font></span></div>
<div dir="ltr" align="left"><span></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff"
face="Arial" size="2">With kind regards,</font></span></div>
<div dir="ltr" align="left"><span></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff"
face="Arial" size="2">Mike</font> </span></div>
<br>
<blockquote style="margin-right: 0px;">
<div dir="ltr" align="left" lang="en-us">
<hr><font face="Tahoma" size="2"><b>From:</b> <a
moz-do-not-send="true"
onclick="return top.js.OpenExtLink(window,event,this)"
href="mailto:rules-users-bounces@lists.jboss.org" target="_blank">rules-users-bounces@lists.jboss.org</a>
[<a moz-do-not-send="true"
onclick="return top.js.OpenExtLink(window,event,this)"
href="mailto:rules-users-bounces@lists.jboss.org" target="_blank">
mailto:rules-users-bounces@lists.jboss.org</a>] <b>On Behalf Of </b>Yang
Song<br>
<b>Sent:</b> 24 August 2007 16:16<br>
<b>To:</b> Rules Users List<br>
<b>Subject:</b> Re: [rules-users] How to catch Exceptions
when firing rules
<br>
</font><br>
</div>
<div>Thanks a lot for the answer, Mark. But I don't think it
makes sense. </div>
<div> </div>
<div>Because in some scenarios, you cannot guarantee the
consequence part of rule is 100% correct -- there could be errors
happening in run-time which are hard to predict, especially when a
complex action or logic will be executed as the concequece. </div>
<div> </div>
<div>There should at least be some mechanisms to tell whoever
fires the rule that there is something wrong during the rule firing
process, then and he can do something, e.g. create a new session. Also
it should enable the rule firer to catch these exceptions and do the
clean up work silently -- instead of leaving these things on the stderr
even cannot be seen in the logs. This will make the program depending
on the JBoss Rules to be more robust. </div>
<div> </div>
<div>What do you think? If JBoss Rules already has the
ability to do this job, can you please let me know?</div>
<div> </div>
<div>Thanks again,</div>
<div>Yang<br>
<br>
</div>
<div><span class="gmail_quote">On 8/24/07, <b
class="gmail_sendername">Mark Proctor</b> <<a moz-do-not-send="true"
onclick="return top.js.OpenExtLink(window,event,this)"
href="mailto:mproctor@codehaus.org" target="_blank">mproctor@codehaus.org
</a>> wrote:</span>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;">
<div text="#000000" bgcolor="#ffffff">Once an exception is
thrown on a conseuqence the current session is considered invalid.
You'll need to add the try catch inside of the actual consequence.<br>
<br>
Mark<br>
Yang Song wrote:
<blockquote type="cite">
<div><span>
<div>Hi, </div>
<div> </div>
<div>Anyone knows how to catch the exception when firing
the rules? </div>
<div> </div>
<div>I wrapped the session.fireAllRules() method using
try...catch, however it doesn't work: when someone wrote bad code in
the rule's action part, the Exception will be thrown and printed to the
stderr, and this will make the rule engine stop working -- the
try...catch outside doesn't help anything. </div>
<div> </div>
<div>If the exception thrown from the rule's action
part can be caught externally, the system can be protected from
interrupting Exception.</div>
<div>
<p><font style="background-color: rgb(255, 255, 255);"
color="#3333ff" face="courier new,monospace">try {<br>
_log.debug("Firing rules in : " + getName());</font></p>
<p><font style="background-color: rgb(255, 255, 255);"
color="#3333ff" face="courier new,monospace">
session.fireAllRules();</font></p>
<p><font style="background-color: rgb(255, 255, 255);"
color="#3333ff" face="courier new,monospace">} catch (Exception e) {<br>
_log.info("Error when firing rules: ", e);<br>
}</font> <br>
</p>
<p>Thanks, <br>
Yang</p>
</div>
</span></div>
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