Duck-Typing all java classes with JRuby, not just interfaces
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Key: JRUBY-3348
URL: http://jira.codehaus.org/browse/JRUBY-3348
Project: JRuby
Issue Type: Wish
Components: Java Integration
Reporter: Kaspar Schiess
Attachments: impostor.tgz
I was told to post this as a jira issue as well: This post introduces a
duck-typing extension for JRuby, extending the possibilities for duck-typing
involving java classes. A working prototype is ready for download. Request for
comments.
Hi all,
When testing java code (jruby, rspec), I frequently want to test code that
takes some argument that I want to mock. If the code looks like this
public void method1(ISomeInterface param) { ... }
everything is fine. If it looks like this
public void method2(AClassThatIsReallyHeavyToConstruct param) { ... }
I am in trouble. JRuby doesn't allow me to cloak my ruby classes as java
classes (duck-typing), only as java interfaces. Sometimes you can inherit from
the class that you want to mock, but as hinted at by the example, this class is
really to fat to construct and let's assume that I can't.
So I hacked together a small prototype [3] that allows me to do exactly that,
using code I've found in jMock 2. The code allows you to
ruby_mock = flexmock(:some_mock) # or whatever
java_mock = DuckType::INSTANCE.transmogrify(ruby_mock,
AClassThatIsReallyHeavyToConstruct.java_class)
yielding a java class instance that looks exactly like a descendant of
AClassThatIsReallyHeavyToConstruct to the JVM, except that it's not. The
instance that you get is a proxy class instance that forwards all calls to the
ruby_mock object.
This obviously solves my problem and I can continue to test. But it is a
kludge; I would really like JRuby to do all this work for me. How about merging
this into JRuby? [1] This looks like a nice addition for the java integration
to me. [2]
I don't know the JRuby code base well enough to integrate this on my own. I am
working on it though - and perhaps someone might be willing to help me with
this?
kaspar
[1] Please disregard the bad state of the java code involved. Especially that
singleton-pattern is probably out of place. But I hope that you can look at
the essence and not at the form. (Which would have to be changed in case of a
JRuby integration)
[2] As far as possible, I've made sure that the original authors are credited.
I took the jMock ClassImpostorizer and special-purposed it. I am also in
contact with the author of the code - he is ok with this new use.
[3] You can fetch the code from http://absurd.li/system/posts/impostor.tgz.
You'll need rspec and possibly some other common stuff installed to be able to
run the specs. If you use this for your own projects, don't forget to include
the .jars in the ./lib dir.
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