Using parsing exceptions as model data

[Bill Boland <bo...@attbi.com>]

In an attempt to display more meaningful and localized error messages
when an exception occurs during parsing a template in the
VelocityServlet, I would like to use the exception information as model
data for an error/troubleshooting view.

For parsing exceptions, it looks like I would have to parse the text
message from the exception to get the information (line/column position,
token encounter, list of tokens expected, etc.). For example, I would
like to display the template source lines surrounding the line and
column where the parsing error occurred to assist the template designer
in diagnosing the problem and possibly suggesting solutions. I would
also like to display the problem in a more localized format, if
possible.

It looks like the ParseErrorException contains only the message from the
ParseException thrown by processing a template. On the other hand, the
ParseException contains much of the detail information that could be
easily be used as model data to display in the error/troubleshooting
view(s). 

An idea: Would it be possible to enhance the ParseErrorException to
encapsulate the ParseException (or information from it) and provide
methods to get to the information it holds? Or simpler, just have it
provide a method to get the ParseException? It looks like the
ParseException has the data but it would need to have getters to get the
data from the public fields (or are public fields accessible via
Velocity?) Of course, the ParseErrorException is also thrown when the
input encoding is not valid (UnsupportedEncodingException) so this makes
it more complex to distinguish what kind of exception is encapsulated. 

Well...just an idea. I hope this makes sense. What do you think? Can you
suggest an alternative to parsing the exception error message?

bill 



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