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JRuby and Java Code Examples

Below are some code examples showing how to call JRuby from Java and how to call Java from JRuby.

Ruby: call_java.rb

  require "java"
  
  include_class "java.util.TreeSet"
  include_class "com.example.CallMe"
  include_class "com.example.ISpeaker"
  
  puts "Hello from ruby"
  set = TreeSet.new
  set.add "foo"
  set.add "Bar"
  set.add "baz"
  set.each { |v| puts "value: #{v}" }
  
  cm = CallMe.new
  cm.hello
  $globalCM.hello
  
  class CallJava
    include ISpeaker
    def initialize
      super
      @count = 0
    end
  
    def say(msg)
      puts "Ruby saying #{msg}"
    end
    
    def addOne(from)
  #    m.synchronize {
        @count += 1
        puts "Now got #@count from #{from}"
  #    }
    end
  end

Java: ISpeaker.java

    package com.example;
    
    public interface ISpeaker {
        public void say(String msg);
        
        public void addOne(String from);
    }

Java: CallMe.java

    package com.example;
    
    public class CallMe {
    
        String mName;
    
        public CallMe() {
            this("Default");
        }
        
        public CallMe(String name) {
            mName = name;
        }
        
        public void hello() {
            System.out.println("Hello from "+mName);
        }
        
        public static void main(String []args) {
            System.out.println("Called main");
        }
    }

Java: CallRuby.java

    package com.example;
    
    import org.apache.bsf.BSFManager;
    import org.apache.bsf.util.IOUtils;
    import org.jruby.Ruby;
    import org.jruby.javasupport.Java;
    import org.jruby.javasupport.JavaEmbedUtils;
    import org.jruby.javasupport.JavaUtil;
    import org.jruby.runtime.Block;
    import org.jruby.runtime.GlobalVariable;
    import org.jruby.runtime.builtin.IRubyObject;
    
    import java.io.FileReader;
    import java.io.IOException;
    
    /**
     * Example of how to:
     * 1. Use java objects in ruby
     * 2. Subclass/implement java objects in ruby
     * 3. Get ruby objects for use in java world
     * 4. Proxy ruby objects for normal use as java objects (interfaces/class)
     */
    public class CallRuby {
    
        public static void main(String[] args) throws Exception {
    
            String dir = "/dclark/workspace/jrubytest/ruby/";
    
            double[] deltas = new double[3];
            for (int i = 0; i < 3; i++) {
                boolean useBSF = (i == 0);
                long start = System.currentTimeMillis();
    
                if (useBSF) {
                    //--- Initialise ruby
                    BSFManager.registerScriptingEngine("ruby", "org.jruby.javasupport.bsf.JRubyEngine", new String[]{"rb"});
                    BSFManager manager = new BSFManager();
    
                    //--- Define a global variable
                    CallMe javaCallMe = new CallMe("globalCallMeInJava");
                    manager.declareBean("globalCM", javaCallMe, javaCallMe.getClass());
    
                    //--- Load a ruby file
                    manager.exec("ruby", "call_java.rb", -1, -1, getFileContents(dir + "call_java.rb"));
    
                    //--- Make a new ruby object
                    String expr = "CallJava.new";
                    ISpeaker ruby = (ISpeaker) manager.eval("ruby", "call_java.rb", -1, -1, expr);
    
                    testMultiThreadsCallingRubyObject(ruby);
    
                } else {
    
                    //--- Initialise ruby
                    final Ruby runtime = Ruby.getDefaultInstance();
    
                    // Need the blank object so can get a nice runtime for the Java.staticMethods calls
                    runtime.eval(runtime.parse("require \"java\"\nclass BlankForJva\nend\n", "BlankForJva.rb", runtime.getCurrentContext().getCurrentScope(), 0));
                    final IRubyObject blankRuby = runtime.evalScript("BlankForJva.new");
    
                    //--- Define a global variable
                    CallMe javaCallMe = new CallMe("globalCallMeInJava");
                    IRubyObject globValue = JavaUtil.convertJavaToRuby(runtime, javaCallMe);
    
                    // Wrap so that all methods are visible to ruby
                    globValue = Java.java_to_ruby(blankRuby, globValue, Block.NULL_BLOCK);
    
                    GlobalVariable globVar = new GlobalVariable(runtime, "$globalCM", globValue);
                    runtime.defineVariable(globVar);
    
                    //--- Load a ruby file
                    runtime.eval(runtime.parse(getFileContents(dir + "call_java.rb"), "call_java.rb", runtime.getCurrentContext().getCurrentScope(), 0));
    
                    //--- Make a new ruby object
                    String expr = "CallJava.new";
                    final IRubyObject rawRuby = runtime.evalScript(expr);
                    ISpeaker ruby;
                    if (i == 1) {
                        // Standard wrapper using Java Proxies
                        ruby = (ISpeaker) JavaEmbedUtils.rubyToJava(runtime, rawRuby, ISpeaker.class);
                    } else {
                        // Or manually wrap ruby object so can be used as the interface (can optionally add synchronization as required on methods)
                        ruby = new ISpeaker() {
                            public void addOne(String from) {
                                //                            synchronized (rawRuby) {
                                rawRuby.callMethod(runtime.getCurrentContext(), "addOne", JavaUtil.convertJavaToRuby(runtime, from));
                                //                            }
                            }
    
                            public void say(String msg) {
                                rawRuby.callMethod(runtime.getCurrentContext(), "say", JavaUtil.convertJavaToRuby(runtime, msg));
                            }
                        };
                    }
                    testMultiThreadsCallingRubyObject(ruby);
                }
                long end = System.currentTimeMillis();
                deltas[i] = (end - start) / 1000.0;
            }
    
            for (int i = 0; i < deltas.length; i++) {
                System.out.println("Took " + deltas[i] + " on pass " + i);
            }
        }
    
        private static String getFileContents(String filename) throws IOException {
            FileReader in = new FileReader(filename);
            return IOUtils.getStringFromReader(in);
        }
    
        public static void testMultiThreadsCallingRubyObject(final ISpeaker ruby) throws InterruptedException {
            Thread t1 = new Thread(new Runnable() {
                public void run() {
                    for (int i = 0; i < 1000; i++) {
                        ruby.addOne("t1");
                    }
                }
            });
            Thread t2 = new Thread(new Runnable() {
                public void run() {
                    for (int i = 0; i < 1000; i++) {
                        ruby.addOne("t2");
                    }
                }
            });
            t1.start();
            t2.start();
            t1.join();
            t2.join();
            ruby.addOne("end");
        }
    }

Note: If you have only simple interface requirements, you can use the second method of proxying the ruby object to include method level synchronization.

Note: BSF calling does not preserve ruby stack traces (add an error to a script and run both ways using the code above).