Passing JRuby objects to Java methods?

Question

How can I pass a JRuby object (it's a quite simple object, containing a few fields of string and Hash type) to a method defined in a Java class?

UPD here is a serialized content of a type I need to share between JRuby and Java code:

--- !ruby/object:LogStash::Event cancelled: false data: &1 message: "q\r" '@version': '1' '@timestamp': 2015-02-17 12:10:17.695000000 Z type: human accessors: !ruby/object:LogStash::Util::Accessors store: *1 lut: type: - *1 - type host: - *1 - host The object is created by JRuby side. Ideally, I could access this object directly from Java and modify it. Less ideally, I need to convert it to something understandable by Java and then back.

kares · Accepted Answer · 2015-02-18 07:25:58Z

1

simply specify an Object or IRubyObject argument signature in the method and it will work just fine when you call the Java method from your Ruby script ...

UPDATE: assuming a LogStash::Event you can either make the Java signature accept (IRubyObject event) and than use event.callMethod("cancelled?").isTrue() and similar on the Java side OR :

... if you mostly only need its @data on the Java side the internal Ruby Hash can be easily retrieved using: event.to_hash pass this to a Java signature accepting (Map<String, ?> eventData) you can easily retrieve eventData.get("message") and even update the data eventData.put("message", 42) it will be reflected on the Ruby side without additional work since Ruby hashes implement the Map interface and thus will be passed around without conversion (it will internally handle simple Ruby to Java string conversion and similar auto-magically)

otherwise (for sanity) I would recommend to introduce a simple bridge object that would wrap the event be passed into Java and handle the use-cases you need to invoke on the Java side.

edited Feb 18, 2015 at 7:25

answered Feb 16, 2015 at 13:02

kares

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3 Comments

kares Over a year ago

your question is a little vague at this point - should have specified a complete use case ... essentially IRubyObject has an API e.g. callMethod you might need to keep a Ruby runtime instance (depending on how you started embed JRuby)

user626528 Over a year ago

I'm calling Java code from JRuby application, not vice versa. I need to pass a Map object to that Java code so it can modify it.

kares Over a year ago

just update your question with details - it simply should work if there's a Map type in the signature (Ruby Hash in JRuby implements Map)

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