Changes:

1. Use new File(...).isAbsolute to detect whether path is absolute, rather than using a custom [probably faulty] regex.
2. Kill unnecessary if on null.

Concerning returning buffered stream to optimize file loads. I have looked into it, but behavior on my SSD seems pretty identical, whether to wrap BuffereInputStream with 8096 buffer or not. To test I've added a system properties to switch between the two strategies and used rails 4 and following command:

bin/jruby -e 'require "benchmark"; puts Benchmark.measure { require "rails/all" }'

Whether I turn buffering or not, the result is usually around 25seconds CPU time (sometimes bumping up to 34 for either case). But maybe that's because seek time is not a factor for SSDs, so I will try it on a regular hard drive on Monday.