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How to access values between JRuby and Java

This is a similar post of the post for Java and Groovy.

Calling JRuby scripts from Java is a bit harder than Groovy, which existing ruby scripts may not be used as it is.

In JRuby,

  • access to an element of Bindings with global variable
  • cannot receive values as command line arguments as ARGV (I'm not sure there is a way)
  • symbol of ruby is represented by org.jruby.RubySymbol, so hard to access a value with it in Java context.
import java.util.Map;
import javax.script.*;

public class JRubyScripting {
	public static void main(String[] args) throws Exception {
		ScriptEngine engine = new ScriptEngineManager().getEngineByName("ruby");
		Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
		bindings.put("counter", 3);
		bindings.put("ARGV", new String[] {"hello", "world"});
		String LF = "\n";
		String code = ""
				+ "puts '$counter: ' + $counter.to_s" + LF
				+ "puts ARGV[0]" + LF
				+ "{'a'=>123, :b=>456}"
		Map vals = (Map)engine.eval(code);
		System.out.println("a: " + vals.get("a"));
		System.out.println("b: " + vals.get("b"));  // b is org.jruby.RubySymbol. it's not easy to access.
		System.out.println("counter: " + bindings.get("counter"));

The output is like

$counter: 3
a: 123
b: null
counter: 3

In order to use jruby ScriptEngine, add a next dependency to pom.xml if you use maven.