From: Armin Roehrl <armin@...>
Date: 2003-06-26T06:22:38+09:00
Subject: Re: Ruby/Java integration through JNI: working implementation

You are a star!!!
>
> This is the idea that popped out during the last discussion in Euruko03.
> (sorry, don't remember the name of the guy who exposed it :)
>
> It has taken me a little bit more than I first thought (the Chinese kept
> me busy :), but 3 days later I have the first working code.
>
> I have created a straight-forward mapping for most of the
> JNI API, which becomes available as a Ruby extension. This
> allows the use of the low-level interface specified in
> http://java.sun.com/products/jdk/1.2/docs/guide/jni/. This part is
> written in C (around 4000 LOCs at the moment).
>
> I have built a simple reflection system that maps Java classes to Ruby
> space, by using the reflection API to get information on all the 
> available
> methods. At the moment it is written in Ruby but it should probably be
> coded in C for speed (this can be done later w/o any problem) and allows
> to call methods transparently as if they were implemented in Ruby.
>
> At the moment, the following is working:
> * creating objects and manipulating native types
> * static methods w/ arbitrary parameters and any return value (native or 
> object types)
> * methods        "                "                   "          "
> * Java objects arrays  * non virtual method calls
> * method overloading (dispatching is performed depending on arg types)
> * seamless conversion of Ruby String and Numeric types to the required
> Java types according to method signatures
>
> Things I have to work on:
> * think about Java exceptions: map them to Ruby or signal them somehow?
> * dynamic definition of Java classes and adding native methods at
> run-time (for instance to call Ruby Procs in callbacks)
> * more automated conversions: Arrays to Java's type[] and vice-versa
> * wrap Java's reflection API completely, providing convenient metaclass
> abstractions & such
> * add more methods to the wrapped Java objects to integrate them better
> w/ Ruby
> * cover more code w/ unit tests (esp. the reflection part)
>
> This is real example of what I'm doing:
>
> Given Simple.java:
>
> public class Simple {
> public String doStuff(String a) {
> return "I was called with argument \"" + a.toString() + "\"" ;
> }
>
> public String doStuff(String a, String b) {
> return a + b;
> }
>
> public boolean compareStrings(String a, String b) {
> System.out.println("I was passed " + a + " and " + b);
> return a.equals(b);
> }
>
> public int compare2(String a, String b) {
> System.out.println("I was passed " + a + " and " + b);
> return a.compareTo(b);
> }
>
> public int sum(String a, String b) {
> System.out.println("Adding " + a + " and " + b + " (inside Java!!!)");
> int i = Integer.parseInt(a) + Integer.parseInt(b);
> System.out.println("The result will be: " + i);
> return i;
> }
> }
>
> I can instantiate the Java object and access its methods from Ruby as
> follows:
>
> require 'reflect'
> require 'rjni'
>
> vm = RJNI::JVM.new "-cp ."
> reflector = RJNI::Reflect.new(vm)
> sclass = reflector["Simple"]
> o = sclass.new_object
> r = o.doStuff("foo passed from Ruby!!!!")
> puts "Result: #{r}"
> r = o.doStuff("hello, ", "world!")
> puts "Result: #{r}"
> r = o.compareStrings("ruby","matz")
> puts "Result: #{r.to_b}"
> r = o.compareStrings("matz","matz")
> puts "Result: #{r.to_b}"
> r = o.compare2("ruby","matz")
> puts "Result: #{r.to_i}"
> r = o.compare2("matz","matz")
> puts "Result: #{r.to_i}"
> r =  o.sum("1", "1")
> puts "Result: #{r.to_i}"
>
> Result:
>
> batsman@tux-chan:~/src/rjni$ 
> LD_LIBRARY_PATH=/usr/local/java/j2sdk1.4.1/jre/lib/i386/:/usr/local/java/j2sdk1.4.1/jre/lib/i386/client 
>
>
> ruby tc_reflect.rb
> Result: I was called with argument "foo passed from Ruby!!!!"
> Result: hello, world!
> I was passed ruby and matz
> Result: false
> I was passed matz and matz
> Result: true
> I was passed ruby and matz
> Result: 5
> I was passed matz and matz
> Result: 0
> Adding 1 and 1 (inside Java!!!)
> The result will be: 2
> Result: 2
>
>
> The code is right now in a state of flux as I am quickly adding
> functionality but I am going through quite fast so I should be able to
> release something soon.
>



-- 

        -A.

----------------------------------------
Armin Roehrl, http://www.approximity.com
We manage risk