Embedding JRuby
Using Java from Ruby is JRuby's best-known feature---but you can also go in the other direction, and use Ruby from Java. There are several different ways to do this. You can execute entire Ruby scripts, call individual Ruby methods, or even implement a Java interface in Ruby (thus allowing you to treat Ruby objects like Java ones). We refer to all these techniques generically as "embedding." This section will explain how to embed JRuby in your Java project.
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JRuby Embed (originally known as Red Bridge)
JRuby has long had a private embedding API, which was closely tied to the runtime's internals and therefore changed frequently as JRuby evolved. Since version 1.4, however, we have also provided a more stable public API, known originally as Red Bridge, now known as JRuby Embed. Existing Java programs written to the raw API's will probably still continue to work, but we strongly recommend Red Bridge for all new projects. Note that using Jruby Embed works well for doing eval of ruby code, and/or sharing a few variables back and forth with a ruby script, but if you want anything more (like new'ing up jruby instances within java, etc.) than that you'll need to code to the raw API's.
Features of Red Bridge
Red Bridge consists of two layers: Embed Core on the bottom, and implementations of JSR223 and BSF (Bean Scripting Framework) on top. Embed Core is JRuby-specific, and can take advantage of much of JRuby's power. JSR223 and BSF are more general interfaces that provide a common ground across scripting languages.
