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From Sebastian Rühl <>
Subject Re: [DISCUSSION] Exception handling during Parsing
Date Mon, 17 Sep 2018 09:57:52 GMT

Small addition for a rule of thumb:
If there is a prober/useful way to react to a error (from dev pov) „user inputs data“
or something other a programmer might need to think about for runtime error a checked exception
is appropriate. For Errors which indicate a programming error one should use Runtime Exceptions
as theses errors should occur in best case only one time (during development) and should bubble
up during unit tests.


> Am 17.09.2018 um 11:39 schrieb Julian Feinauer <>:
> Hey Chris,
> yes, checked exceptions and Lambda 8 are... kind of not perfect.
> Therefore I suggest the addition of an UncheckedInvalidFieldException which wraps the
checked exception for the lambda or the stream. This is similar to how the JDK suggests to
handle IOExceptions (with the UncheckedIOException).
> But I think the question is more about the user perspective than the implementation and
I see good arguments for both sides. And I do see the point that its harder to react to this
kind of exception but in a situation like ours the reaction could be 
> * more detailed exception (nobody cares about what kind of uncheked exceptions are thrown
from a function)
> * I see situations where this can lead to a runtime handling, e.g., givin the user another
prompt to reenter or the possibility to fix its configuration file and reload
> For me it just felt "unsafe" to just do the parsing and hope that everything goes smooth,
this is way I went to action.
> Julian
> Am 17.09.18, 11:32 schrieb "Christofer Dutz" <>:
>    Hi Julian,
>    I can imagine that ... we were having some discussions about stuff like that. 
>    The thing is, that a checked exception should give the application a chance to react
to something. If we use an invalid address, there's sort of nothing we can do about that.
And while I like checked exceptions too ... all this Lambda Java 9 stuff seems to have problems
with them. They seem to get gobbled up without notice. Runtime exceptions however seem to
be able to bubble up.
>    Also do Checked exceptions make it difficult to write code like this:
> -> builder.addField(queryString));
>    So with these runtime exceptions you have the ability to catch them and react on them,
but you don't make things too complicated for people using Lambdas.
>    Hope I got this right (Sebastian, please correct me if I got this wrong)
>    Chris
>    Am 17.09.18, 11:27 schrieb "Julian Feinauer" <>:
>        Hi all,
>        I just opened a PR where I made the PlcInvalidFieldException checked.
>        Sebastian commented on the PR and states that he would prefer an unchecked Exception.
>        So I suggest we discuss the matter and think about the exception handling strategy.
>        Why do I think a checked exception is better?
>        When users use plc4j they provide their own address and source strings. Here,
three kinds of failures can occur:
>          *   The string contains an error (e.g. copy paste)
>          *   The string does not belong to the connection (S7 address for Beckhoff connection)
>          *   The address does not exist
>        The third case is handled later on.
>        But I assume the first two errors to be (at least) equivalent frequent if not
far more common to occur.
>        Thus, I prefer to notify the code users to handle this case explicitly to give
their users feedback that they entered a “bad string”.
>        Futthermore, especially in stream processing contexts things like
>        Try {
>        // do something…
>        } catch (Exception e) {
>        Logger.warn(“Problem during processing of element…. “)
>        }
>        Is used.
>        From my perspective, the case where I have bad input data is different and would,
if catched and logged silently lead to a number of equal log entries, as each processing step
would simply fail.
>        In this case I think its important to notify the stream developer of the fact
that he cant event start his stream processing.
>        Sebastian states:
>        In my opinion errors like these should always be runtime errors as theses a programming
errors (e.g. ArrayIndexOutOfBoundException) and can't be handled properly at runtime so no
need to check them. In contrast if this error could happen at runtime like a connection drop
for reconnects etc. than it worth to enforce the catching of this exception so the developer
can implement his own handling of this. But in this case in most cases the try catch would
in most cases don't contain any useful code as the address ist unlikely to change at runtime
(errors resulting in a parsing error)
>        What do others think, how should we generally deal with User Input and checked
/ unchecked exceptions?
>        Julian

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