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From Julian Feinauer <>
Subject [DISCUSSION] Exception handling during Parsing
Date Mon, 17 Sep 2018 09:26:50 GMT
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
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


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