From: Jeremy Schneider <jeremy@...>
Date: 2009-05-13T12:17:34+09:00
Subject: only able to capture last exception

I am writing a script to validate some documents against an XSD.  When a 
document does not validate, I want to provide all the available 
information about the reason(s) why it does not validate. 

My problem is that it looks like two exceptions are raised in the 
process of validating a document, but my method for dealing with the 
exceptions only captures the last exception, and I would like to capture 
all the exceptions.

Below is my program and its output.  As you can see, two error messages 
end up being sent to standard error, but the rescue part only captures 
one (the last) error message.

Is there a good way to capture all of the exceptions generated in the 
call to validate?  I could play tricks like running the validation as a 
system command and then parsing the standard error, but that seems very 
clunky, and it feels like there should be a better way.  I have tried 
searching with Google and reading various references about exception 
handling in Ruby, and not found the answer.  Maybe I just don't know the 
right terms to use.

Please forgive my naive Ruby code below.  I'm just starting out, 
obviously.   Thanks for any assistance or guidance.

jeremy@jeremy-ubu810:~/xmlplay$ cat XML_Demo_5.rb
require 'rubygems'
require 'xml'

def myvalidate(theXMLDoc, theXSD)
  valid = false
  begin
    theXMLDoc.validate(theXSD)
  rescue StandardError => e
    puts "message is: (#{e.to_s}); caller is: " + caller.inspect
  else
    valid = true
  end
  return valid
end

dtd = XML::Dtd.new(%{<!ELEMENT rubycookbook (recipe+)>
<!ELEMENT recipe (title?, problem)+>
<!ELEMENT title (#PCDATA)>
<!ELEMENT problem (#PCDATA)> })

puts "Validation should fail:\n"

open('cookbook2.xml', 'w') do |f|
  f.write %{<?xml version="1.0"?>
<rubycookbook>
 <recipe>
   <title>A recipe</title>
   <title2>A recipe</title2>
 </recipe>
</rubycookbook>
}
end

document = XML::Document.file('cookbook2.xml')

if myvalidate(document,dtd)
  puts "\nThe document was valid."
else
  puts "\nThe document was not valid."
end
 

jeremy@jeremy-ubu810:~/xmlplay$ ruby XML_Demo_5.rb 2> stderr
Validation should fail:
message is: (Error: No declaration for element title2 at 
cookbook2.xml:5.); caller is: ["XML_Demo_5.rb:36"]

The document was not valid.
jeremy@jeremy-ubu810:~/xmlplay$ cat stderr
Error: Element recipe content does not follow the DTD, expecting (title? 
, problem)+, got (title title2 ) at cookbook2.xml:3.
Error: No declaration for element title2 at cookbook2.xml:5.
jeremy@jeremy-ubu810:~/xmlplay$