require jruby seems to work and fail simultaneously - ruby

Question

John-Breedloves-Mac-mini:~ john_breedlove$ irb
>> require 'jruby'
=> true
>> require 'zxing'
RuntimeError: ZXing requires JRuby
from /Library/Ruby/Gems/1.8/gems/zxing-0.1.1/lib/zxing.rb:1
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:36:in `gem_original_require'
from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:36:in `require'
from (irb):2
>>
How is this possible?
Further, how would I write that in a ruby script, though?
I have a file I want to execute called test.rb, which contains the following:
require 'rubygems'
require 'jruby'
require 'zxing'
ZXing.decode 'test.png'
I am executing it from the command-line like so:
ruby test.rb
In this context, how do I include java? Or is this even possible?

Answer 1

You are using the JRuby gem, rather than the JRuby itself.
JRuby (which ZXing is checking on line 1) is a module that gets defined only after you require 'java' in JRuby.
This should be clearly stated in ZXing's documentation, but it doesn't seem to be.
Here's the test output when I run the following from cloned ZXing source code:
$ ruby -v -I lib -r zxing -e 'p 0'
ruby 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]
./lib/zxing.rb:1: ZXing requires JRuby (RuntimeError)
$ jruby -I lib -r zxing -e 'p 0'
/Users/asari/Development/src/zxing.rb/lib/zxing.rb:1: ZXing requires JRuby (RuntimeError)
from /Users/asari/Development/src/zxing.rb/lib/zxing.rb:1
...internal jruby stack elided...
from (unknown).(unknown)(/Users/asari/Development/src/zxing.rb/lib/zxing.rb:1)
from (unknown).(unknown)(:1)
$ jruby -r java -I lib -r zxing -e 'p 0'
0