rjni: Java binding for Ruby through JNI
What is rjni?
rjni exposes the Java Native Interface to Ruby. This allows the
programmer to instantiate Java objects, manipulate them, define Java
classes, etc.. from Ruby.
Note that rjni is not meant to embed Ruby into Java, although it
can be used to ease integration in that case.
For the time being, the same as Ruby. Might switch to LGPL in the
Please don’t hesitate to contact me to criticize, suggest new
features or help with the development :)
- The APIs are quickly stabilizing.
- The base layer still needs some work and further testing.
- Several low-level issues remain to be solved.
- The higher-level APIs have yet to be documented and tested rigorously.
- almost complete mapping of JNI to Ruby
- functional mapping of java.lang.reflect
- Java exceptions are caught and transformed into Ruby’s
- automagic reflection:
- getting metaclass objects representing classes
- Java object instantiation from Ruby
- static methods become class singleton methods
- Java method dispatching from Ruby considers overloading
- some basic type conversions (String <=> java.lang.String,
- automatic accessors for fields:
- readers: javaobject.field?
- setters: javaobject.field = value
Get the sources.
WARNING: THIS IS A TECHNOLOGY PREVIEW. THE SOFTWARE IS NOT EVEN ALPHA
QUALITY AT THE MOMENT AND IS NOT MEANT TO BE USED YET. IT IS ONLY PROVIDED
TO PRESENT THE TECHNIQUES EMPLOYED AND (HOPEFULLY) TO ACCELERATE THE
Please refer to the current documentation.
This technology preview is meant to illustrate the possibilities offered by
rjni. It is by no means a usable library yet. The build process is
quite tricky, as it involves linking against the Java libraries and is
therefore highly system-dependent.
The steps are:
- Setting up build environment
ruby install.rb config
You might need to specify the location of your J2SDK with the following
ruby install.rb config \
You have to replace the paths above by the appropriate values for your
local Java installation. Note that rjni has been tested with
Blackdown 1.4.1, and, although it should be possible to build it with other
JSDKs, compilation and/or linking might fail unless you get the above
options right (or end up modifying the Makefiles by hand).
- Compiling & installing
ruby install.rb setup
ruby install.rb install
- You can now run the the tests and examples in test/ and
examples/ You will notice a short pause after the execution of the
scripts. This is normal and expected at the moment. Sometimes a
ruby might stay around after termination of the script; you can
kill it manually.
Sometimes ld.so will be unable to resolve symbols at runtime; you
will then need to set the LD_LIBRARY_PATH environment variable to
some sensible value.
rjni offers the following 3 API:
- a low-level straight-forward mapping of the Java Native Interface to Ruby.
All operations on Java objects and classes are ultimately performed through
- a direct conversion of java.lang.reflect and associated classes to Ruby. It
is built upon RJNI. Usage of this API is not recommended since it
offers no significant advantages against the 2 others, and is fairly slow.
- magic reflection of Java objects to Ruby, such that they can seemingly be
manipulated exactly like Ruby objects. This involves automatic method
dispatching, singleton class abstraction (static methods become singleton
methods of the class object), some automatic type conversions, attribute
setters and getters, etc.