CSV.foreach("aa.csv", {:encoding => 'utf-8'}) do |row|
end
puts 'read ok'

pc:test$ ruby test.rb 
read ok
pc:test$ jruby  test.rb 
ArgumentError: invalid byte sequence in UTF-8
               =~ at org/jruby/RubyRegexp.java:1520
               =~ at org/jruby/RubyString.java:1740
  init_separators at /opt/local/share/java/jruby/lib/ruby/1.9/csv.rb:2058
       initialize at /opt/local/share/java/jruby/lib/ruby/1.9/csv.rb:1590
             open at /opt/local/share/java/jruby/lib/ruby/1.9/csv.rb:1349
          foreach at /opt/local/share/java/jruby/lib/ruby/1.9/csv.rb:1207
           (root) at test.rb:273