[seam-issues] [JBoss JIRA] Commented: (SEAMCATCH-31) change terminology for exception type hierarchy traversal

[Jozef Hartinger (JIRA)]

    [ https://issues.jboss.org/browse/SEAMCATCH-31?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12571093#comment-12571093 ] 

Jozef Hartinger commented on SEAMCATCH-31:
------------------------------------------

IMHO these are two different things. 

Currently, the ASCENDING/DESCENDING setup controls the order of handlers based on the exception chain. According to the docs there are two phases during exception handling (http://docs.jboss.org/seam/3/catch/latest/reference/en-US/html/client_usage.html#client_usage.traversal)

DESCENDING - where the chain is being traversed from the outer most exception to the root cause
ASCENDING - where the same chain is being traversed from the root cause to the outer most exception

for every exception in the chain, handlers for supertypes of the exception are called (depth first)

IMHO your proposal changes the semantics of traversal mode. It removes the chain traversing completely (it is traversed only once) and it uses the traversal mode to control the order in which handlers for different types of an exception type tree are called.

To ilustrate:

3SS
|
3S
|
3 --> 2 --> 1

3SS is a superclass of 3S
3S is a superclass of 3
3 is caused by 2
2 is caused by 1

So far the traversal mode controlled the horizontal axis. I think that what you propose modifies it to control the vertical axis.

> change terminology for exception type hierarchy traversal
> ---------------------------------------------------------
>
>                 Key: SEAMCATCH-31
>                 URL: https://issues.jboss.org/browse/SEAMCATCH-31
>             Project: Seam Catch
>          Issue Type: Feature Request
>          Components: Core API
>    Affects Versions: Alpha2
>            Reporter: Dan Allen
>            Assignee: Jason Porter
>             Fix For: Alpha3
>
>
> There appears to be some confusion about what the traversal path means. We've come up with some better terms that should help users understand how to use it.
> When one of the exceptions in the stack trace is being handled, the handlers for that exception are notified in a particular order. That order is based on the type hierarchy of the exception. The traversal seeks to address this scenario:
> Assume that a group of exceptions have a common super class. You may choose to write a handler that catches all of those exceptions by handling that super type. We'll call that a category handler, where the super class represents a category (i.e., SQLException) So the question you have to ask yourself, then, is: 
> Do you want your category handler to be notified before or after the handler for the subtype gets notified?
> You specify you want the category handler to be notified before by adding the attribute during = TraversalPath.DESCENDING to the @Handles exception.
> However, this descending/ascending isn't catching on. Tree traversal is more commonly referred to using the terms breadth-first or depth-first. Catch notifies breadth-first handlers before depth-first handlers, in the order of the tree traversal (walking the exception type hierarchy).
> Therefore, these attribute values would make more sense:
> during = TraversalMode.BREADTH_FIRST
> during = TraversalMode.DEPTH_FIRST (default)
> If you write a SQLException handler with during = TraversalMode.BREADTH_FIRST, then it will be notified before a handler for BatchUpdateException.  

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