How to initialize Java objects from a ruby script being executed by ScriptingContainer in JRuby?

Question

Java code executing a Ruby script:

ruby = new ScriptingContainer(LocalVariableBehavior.PERSISTENT);
ruby.put("MyJavaClass", MyJavaClass.class);
ruby.runScriptlet(readFile("Test.rb"));

MyJavaClass code:

public class MyJavaClass {
    public MyJavaClass(String name) {
        System.out.println("I got a name: " + name);
    }
}

Ruby code within Test.rb:

someInstance = MyJavaClass.new("Joe")

This is what I tried to initialize a Java object within a Ruby script using JRuby. It did not work.

Sébastien Le Callonnec · Accepted Answer · 2013-01-08 23:58:39Z

1

First, notice that by putting MyJavaClass.class as a ruby variable, the Java Class object available is made available to your JRuby script. The following works:

java_class = MyJavaClass.getDeclaredConstructor(java.lang.String.java_class)
someInstance = java_class.new_instance("Joe")

It uses Java reflection to instantiate MyJavaClass.

However, this can be done more simply without adding the class as ruby var. First, ensure the path of the folder of MyJavaClass is on the classpath (or ruby $LOAD_PATH). Then, call the class as follows in Test.rb.

someInstance = Java::MyJavaClass.new("joe")

or

 java_import 'MyJavaClass'
 someInstance = MyJavaClass.new("Joe")

answered Jan 8, 2013 at 23:58

Sébastien Le Callonnec

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