What is the best way to get JRuby to run in 2.0 mode?
For a specific script, you can use the --2.0 option:
jruby --2.0 -S rails s
For setting 2.0 as the default value, set JRUBY_OPTS:
export JRUBY_OPTS=--2.0
You can also set the value in ~/.jrubyrc:
compat.version=2.0
来源：https://stackoverflow.com/questions/15281036/how-to-run-ruby-2-0-with-jruby-1-7