Re: [rules-users] How to do Exception Handling???
@Kris Do you have any tips for this? Am I interpreting your AbstractWorkItem implementation for exception handling correctly. Anybody else is very welcome to comment as well. Thanks, Nick. -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p725237.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
@Kris Thanks for the input. While I keep investigating on my side I thought of asking you this quick question given that you said this might be trivial to do I am implementing an AbstractWorkItemHandler that catches exceptions and the intention is to map these to Faults with the same name. (just as you mentioned) I then would like to raise a Fault from my AbstractWorkItemHandler and handle these faults with Process Exception Handlers that might signal an event for further processing of the Fault. Now the question is: Can I raise a Fault programmatically in my AbstractWorkItemHandler (i.e. without having any Fault Nodes in my workflow definition) ? If yes, how can I do this? Please let me know if you have any question. Thanks, Nick. -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p718847.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
The main problems I see when translating a java exception to a process exception automatically: - the exceptions are too low level, no business user understands NumberFormatException or ClassCastException, and the error could come from deep inside the invoked service - by making it automatic, the user is not forced to think about it and thus might forget about it, so you might end up with aborted process instances (default behaviour if no exception handler can be found) and the user won't even notice - the handler is actually the link between the process engine and the environment, I see it as a contract between the two, and what data is exchanged (input/output) is defined It is trivial to simply create an AbstractWorkItemHandler that would transform a Java exception to a process fault with the same name. If you want this as the default behaviour, I suggest you do that. But if we build this into the framework, it will be more difficult to change it if you don't want this behaviour (and we try to keep the maximum flexibility possible). Kris If every workitem needs to have a try / catch block, just to make sure that all possible exceptions are handled gracefully, would not that be a framework concern to have a mechanism that _converts_ these exceptions to some return error parameters (just contemplating here) OR to allow a workitem node to take an ExceptionHandler that would signal an event or convert it to the result parameter, etc..? I understand that you are coming from the fact that Java Exceptions are too low level, and are not Process Exceptions, but they really are :) [something went kaboom within the _Process_] just need to be converted to ones, and it would be a natural concern for a Java framework. One custom approach that I am thinking about so far is to wrap all workitems with AfterThrowing advice to do just that, but again this rather feels like a work around. Thank you, /Anatoly P.S. By the way, would be cool to address real Java Exceptions (no matter what the approach is) in Exception Handling section of the documentation :) -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p707668.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
I'm not convinced that converting a java exception to a process fault with the same name is a solid behaviour. In java it is perfectly permissible and valid for a piece of code to change the exception it throws to a subclass of that exception (eg throw a FileNotFoundException instead of a generic IOException). Any legacy code which catches the IOException will keep working perfectly (unless they are do something really stupid). However drools would be doing something stupid, it would be matching based upon the exception name not type hierarchy and the flow would suddenly break when you no longer have the right fault handler matching the right exception name. I'd suggest the more sensible and solid default action would be to create of a fault with a name UnhandledException (and the exception as a payload). This could be extended later so that a map from exception type - fault name could be produced using the same matching logic as catch blocks. Thomas -Original Message- From: rules-users-boun...@lists.jboss.org [mailto:rules-users- boun...@lists.jboss.org] On Behalf Of tolitius Sent: 12 April 2010 16:19 To: rules-users@lists.jboss.org Subject: Re: [rules-users] How to do Exception Handling??? Kris Verlaenen wrote: It is trivial to simply create an AbstractWorkItemHandler that would transform a Java exception to a process fault with the same name ...But if we build this into the framework, it will be more difficult to change it if you don't want this behaviour (and we try to keep the maximum flexibility possible). Kris Seems like a perfectly solid default behaviour to me. Features like this one are usually done (changed only if needed) via configuration. Convention Over Configuration applies to Java frameworks as well :) /Anatoly ** This message is confidential and intended only for the addressee. If you have received this message in error, please immediately notify the postmas...@nds.com and delete it from your system as well as any copies. The content of e-mails as well as traffic data may be monitored by NDS for employment and security purposes. To protect the environment please do not print this e-mail unless necessary. NDS Limited. Registered Office: One London Road, Staines, Middlesex, TW18 4EX, United Kingdom. A company registered in England and Wales. Registered no. 3080780. VAT no. GB 603 8808 40-00 ** This message is confidential and intended only for the addressee. If you have received this message in error, please immediately notify the postmas...@nds.com and delete it from your system as well as any copies. The content of e-mails as well as traffic data may be monitored by NDS for employment and security purposes. To protect the environment please do not print this e-mail unless necessary. An NDS Group Limited company. www.nds.com ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
@Thomas, That is exactly what I mean. Have a default language exception handling mechanism, by which all unmapped exceptions would be converted to ProcessRuntimeException and will go to the Fault with type, let's say, UnknownProcessExceptionFault. And have an option to turn this behaviour off, if needed, of course. And have an option to map other exceptions to Fault nodes as simple as: util:map id=processExceptions entry key=SomeBusinessException value=SomeBusinessProcessExceptionFault/ entry key=SomeOtherBusinessException value=SomeOtherBusinessProcessExceptionFault/ entry key=SomeCoreJavaException value=SomeCoreJavaExceptionFault/ ... ... ... /util:map ( this is a Spring map, but you can look at it as a regular Java MapK, V ) /Anatoly -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p714053.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
tolitius wrote: would be cool to address real Java Exceptions (no matter what the approach is) in Exception Handling section of the documentation +1 -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p708627.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
salaboy wrote: Ed, feel free to contribute with documentation about how you implement your own mechanisms to handle exceptions. I'm a newbie, I've never written a WorkItemHandler, I've just read the doc and tried to understand. I came away from the Exceptions section of the doc with no idea of whether or how it related to Java Exceptions, and they're not covered elsewhere. All I'm looking for (for now) is to simply throw into the docs (maybe in 8.2.4. Executing work items) what Kris said here, which I think boils down to: WorkItemHandlers should not throw exceptions of any kind. If an exception is to be handled at the business process level, convert it into a Fault. The WorkItemHandler should also provide whatever other handling (logging, etc.) is desired. I'd also suggest renaming section 3.8 from Exceptions to Faults, and talk about Fault Handlers, not Exception Handlers. It might make sense to provide an AbstractWorkItemHandler which wraps executeWorkItem() with sensible default behavior of some kind. But this is less important, IMHO. I agree that the mapping from Java exception to business-process semantics is fundamentally the responsibility of the WorkItemHandler. The framework can help, and can make clear that the responsibility exists -that's all. -Ed -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p708851.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
Miguel,
I think your work item handler should not be throwing an exception, just
because a java exception is low-level and linked to one specific implementation
and we try to keep the processes a little higher-level.
So what could you do then to model exceptional situations when executing a work
item? I suggest you use a try-catch block to catch the java exception and
translate that into something higher-level, like:
- your work item can contain result parameters, in case of some failure you
could fill in a special result parameter with some data, the process instance
can then map this result data to some process variable which will allow you to
use this data, for example in a XOR split node immediate after this work item
node to check for exceptional situations, or in an on-exit action linked to the
workItemNode (which could then for example also throw a fault so that the
nested exception handler mechanism kicks in)
- your work item handler could decide to send a signal to the process instance
to signal the occurrence of some exceptional event, and you could use an event
handler to listen to that event
Depending on your exact use case, I can probably think of a few more
alternatives (like using abortWorkItem instead of completeWorkItem), but they
might not be all ready to use out-of-the-box.
Kris
- Original Message -
From: miguel machado
To: Rules Users List
Sent: Thursday, April 01, 2010 1:57 PM
Subject: Re: [rules-users] How to do Exception Handling???
Hi,
I'm not sure this will help you out, but in what comes to the system i'm
currently developing (using drools expert), i've got this method
runRuleEngine that collects facts and fire rules on them and i am able to
catch any sort of error within the drools execution by surrounding that with
try {} catch (Exception e) {}.
The important part is that it took me a while to figure that out cuz eclipse
didn't force me handle that, as if the called method didn't have throws (it
usually shows a compilation error otherwise, right?).
Just a thought.
_ miguel
On Wed, Mar 31, 2010 at 9:44 PM, nanic23 nani...@hotmail.com wrote:
I have a ruleflow that handles exceptions when they are raised by a Fault
node but I am not being able to accomplish the same if an exception is
thrown by a workItem or an action node instead.
I have a workItem node with a work item handler that throws a
RuntimeException. My exception handler in the composite node is not catching
this exception.
So, question
1) how can I handle runtime exceptions thrown by my workItemHandlers?
2) how can I get a hold of the exception to log the stack trace?
Any ideas or tips are very appreciated.
Nick.
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Re: [rules-users] How to do Exception Handling???
@Kris, If every workitem needs to have a try / catch block, just to make sure that all possible exceptions are handled gracefully, would not that be a framework concern to have a mechanism that _converts_ these exceptions to some return error parameters (just contemplating here) OR to allow a workitem node to take an ExceptionHandler that would signal an event or convert it to the result parameter, etc..? I understand that you are coming from the fact that Java Exceptions are too low level, and are not Process Exceptions, but they really are :) [something went kaboom within the _Process_] just need to be converted to ones, and it would be a natural concern for a Java framework. One custom approach that I am thinking about so far is to wrap all workitems with AfterThrowing advice to do just that, but again this rather feels like a work around. Thank you, /Anatoly P.S. By the way, would be cool to address real Java Exceptions (no matter what the approach is) in Exception Handling section of the documentation :) -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p707668.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
The way I see it, you can attach an arbitrary number of fault handlers to a given running process. All that is needed is for the process to have one or more fault nodes having fault names which are handled by the fault handlers of the process. It in in these fault handlers that I raise custom/application-specific exceptions. I've personally found this fault/fault handler concept to be pretty flexible in terms that the process failure/exception logic resides at a single location viz. the fault handler of the process. This is more-so conversant with the workflow terminology i.e. there are no exceptions, just logical faults which are not checked/unchecked and have no logical meaning of a stack-trace. Just my 2 cents. Peace, /T\ -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p701157.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
@Touma, What you are saying make sense, and while it does, it still does not answer the questions above: Let me simplify it a little: You have a workitemhandler throwing a RuntimeException. How to make sure this RuntimeException is propogated to that Fault node? Thank you, /Anatoly -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p702114.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
+1 Documentation on this is unclear. Unit tests in drools-src handle exceptions using Fault nodes, but not real exceptions that are thrown by WorkItemHandlers. 1. Can I have Process or Composite node exception handlers catch my own (or any other) exception other than just Faults? and if so, how can accomplish that? How I register my custom exception handler? 2. If the above is possible... How can I pass the exception to the custom exception handler so I can work with it (log the stack trace, etc)? /Anatoly -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p693018.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
Re: [rules-users] How to do Exception Handling???
What I'm trying to do is a little different I have a ruleflow with a workItem node which has a workItemHandler behind it. My workItemHandler will call an external system which might throw an exception. I DO NOT want to catch the exception in the code (or I might but after doing something with the exception I will re-throw a runtime exception from my workItemHandler). I want to have a Process or Composite node ExceptionHandler to catch this runtime exception and then signal an event to do the real handling (work). I have been able to do this but only with drools Faults. So, the only type of exception that I am being able to handle with the Process or Composite node handler are FAULTS being raised by a Fault node. If I throw a runtime exception from within my workItemHandler the ExceptionHandler defined in the Process or Composite node is not catching it. So, my questions are: 1. Can I have Process or Composite node exception handlers catch my own (or any other) exception other than just Faults? and if so, how can accomplish that? How I register my custom exception handler? 2. If the above is possible... How can I pass the exception to the custom exception handler so I can work with it (log the stack trace, etc)? Any ideas? Thanks, Nick. -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p690938.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
[rules-users] How to do Exception Handling???
I have a ruleflow that handles exceptions when they are raised by a Fault node but I am not being able to accomplish the same if an exception is thrown by a workItem or an action node instead. I have a workItem node with a work item handler that throws a RuntimeException. My exception handler in the composite node is not catching this exception. So, question 1) how can I handle runtime exceptions thrown by my workItemHandlers? 2) how can I get a hold of the exception to log the stack trace? Any ideas or tips are very appreciated. Nick. -- View this message in context: http://n3.nabble.com/How-to-do-Exception-Handling-tp689387p689387.html Sent from the Drools - User mailing list archive at Nabble.com. ___ rules-users mailing list rules-users@lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users
