John Miller wrote:
> Greetings All,
> 
> I have concluded that I ought to try out JRuby.  Running on windows I
> get the short end of the stick when it comes to non-ruby-native
> functionality, and there is an AI package in Java that I want to play
> with in a language that doesn't require a novel worth of code to use.  I
> have a few questions about how to make this happen:

I'm late to the party on this one, but here's some answers.

> 1) What is the best way to get MRI and JRuby to live on the same
> (Windows) system?  The only answer I've found to this question involves
> bash scripts.

Generally, JRuby lives entirely within its unpacked directory. Run 
<jruby dir>/bin/jruby and it will handle the rest. If you add JRuby's 
bin dir to your path, you can just run "jruby". If you add it after your 
Ruby path, and want to make sure you're running 'gem', or 'rails' or 
other scripts with JRuby, use "jruby -S <scriptname>".

> 2) What do I need to get in terms of a Java Environment.  below is the
> output of Java -version:
>   java version "1.4.1_03"
>   Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_03-b02)
>   Java HotSpot(TM) Client VM (build 1.4.1_03-b02, mixed mode)
> This was likely installed at least 3 years ago, and is probably out of
> date.  I went to java.sun.com to look for "the latest version" and hit
> buzzword central.  The last time I did anything more then run a Java App
> was 6+ years ago and I'm now lost in all the new Lingo.  So, what to I
> need to run JRuby, and what else outh I get to make Rails work with it?

JRuby 1.1+ requires at least Java 5, but Java 6 (Java SE 6, someone else 
posted info on how to download) will provide the best performance. 
Install it and that should be all you need.

Unless you're going to compile Java code, you don't need the compiler. 
JRuby's compiler is self-contained.

> 3) Is is possible to "move" my installed gems from MRI Ruby1.8.6 to
> JRuby without having to touch the network.  All I have is a 56.6k modem,
> and Downloading rails again is a 4 hour job. (BTW: Is there a way in
> general to download a gem and not install it? For example could I get
> the latest Rails release on my Laptop at work and bring the files home
> to install on the desktop?)

Well for Rails, you shouldn't have any problems. Rails installs the same 
gems under any Ruby implementation, so your already-downloaded gems 
(under lib/ruby/gems/1.8/cache) can be installed in JRuby. I don't know 
of a way to just fetch a gem and not install.

> 4) What does it take to get SQLite or some equivalent no configuration
> database running in JRuby?

Your best bet would be a database like Derby/JavaDB, which is a 
pure-Java embedded database. Using JavaDB, you could produce a DB-driven 
app very quickly, and since it's Java the whole app could be packaged up 
and moved to another machine and run just as well. If you're using 
ActiveRecord, there are gems for derby and other databases. If you're 
not using ActiveRecord, it would probably be easiest to just call JDBC 
APIs directly. There are blog posts and wiki articles out there that 
show how to directly use JDBC from Ruby with JRuby.

Do check out the JRuby Wiki at http://wiki.jruby.org and feel free to 
join the mailing lists or find us on #jruby on Freenode IRC.

- Charlie