C Extension Alternatives

JRuby does not support native C extensions, but it does have its own Java native extensions API. Several gems have implementations of both Java and C extensions rolled into the same gem and those will not be listed here since they will just work. In some cases there is a JRuby version with a slightly different name or possibly even a totally different name and we list these here so you can update your Gemfile:

gem 'therubyracer', platform: :mri
gem 'therubyrhino', platform: :jruby

When there is not an exact match some gems come close enough where a little work on your part can make your application compatible with JRuby.

This page lists common C extensions and JRuby-friendly alternatives you can use to replace them.

If you are interested in helping us port an extension to JRuby, this article is helpful: Your first Ruby native extension: Java see also JRuby examples for a maven build.

Gem	Suggestions
bson_ext	bson_ext isn't used with JRuby. Instead, some native Java extensions are bundled with the bson gem.
charlock_holmes	Use charlock_holmes-jruby instead.
curb	Rurl is an example how to implement some of curb's functionality using Apache HttpClient
curses	Use ffi-ncurses. ncurses is literal API and lower level than curses
fast_xor	use xorcist instead or roll slower but pure ruby equivalent.
escape_utils	Most of the escape methods here are now native code in CRuby and JRuby for the CGI library. Others can be found in the JDK itself.
image_science	Use image_voodoo instead.
kyotocabinet	Try using kyotocabinet-java instead. This isn't 100% complete yet, but it covers most of the API.
memcached	Try using jruby-memcached instead. Alternatively you can use jruby-ehcache, a JRuby interface to Java's (JSR-107 compliant) Ehcache.
mysql	Use activerecord-jdbcmysql-adapter.
mysql2	Use activerecord-jdbcmysql-adapter.
oj	Try gson, json or json_pure instead.
pg	Use activerecord-jdbcpostgresql-adapter instead or pg_jruby (drop-in replacement).
pry-byebug	Use pry-debugger-jruby instead.
RDiscount	Use kramdown, Maruku (pure Ruby) or markdown_j (wrapper around a Java library)
RedCarpet	Same as with RDiscount use alternatives such as kramdown, Maruku or markdown_j
RMagick	Try RMagick4J (implements ImageMagick functionality in Java) or preferably use alternatives mini_magick & quick_magick. For simple resizing, cropping, greyscaling, etc look at image_voodoo. You can also use Java's Graphics2D.
sqlite3	Use activerecord-jdbcsqlite3-adapter.
therubyracer	Try using therubyrhino instead (or dienashorner on Java 8+).
Thin	Use Puma.
Unicorn	Use Puma.
win32ole	Use the jruby-win32ole gem (preinstalled in JRuby's Windows installer).
yajl-ruby	Try json or json_pure instead. Unfortunately there is no known equivalent JSON stream parser.
rugged	Try using rjgit. Not a drop-in replacement, but API is pretty similar

Please add to this list with your findings.

*Note that the JRuby-Lint gem parses the contents of the list above to use for its Ruby gem checker. In order for JRuby-Lint to use the information, please adhere to the table format above and the links to projects below (in the source for this page).