JRuby on Rails Tutorial

JRuby on Rails - RailsConf 2007 Tutorial

Advantages:
Take advantages of existing Java libraries
Run on Java infrastructure
Supports Java's multibyte/unicode strings.
Support Ruby's thread API, one native thread = one system thread, good multicore use.
True concurrent threading.

Great progress in the past year. From barely running rails 1.1 last year to running all of rails (except some lowlow demand dark corners) now, with good performance on everything but RDoc.

Most Gems just work. Anything pure Ruby (or with a JRuby port) runs.
Webrick works.
JRuby port of Mongrel works.

Differences:
1-Database support
Pure Ruby drivers work - mySQL
All the JDBC drivers you'd want to use work. (Yay!) (Some need custom coding to support migrations.
JDNI for connection pooling (More yay!)

2-No Native Extensions
Unless there's a port.
Mongrel - done
Hpricot - done
Database support - some done, some in progress
RMagick - in progress

3-Command-line Performance
Very good (possibly faster) once you're running, but typical java-slow startup performance.

Deployment
1. Mongrel works well. No process forking, process management
But why? Use Java App Servers via GoldSpike (or rails-integration) plugin.
2. Build WAR files for Rails apps.
One plugin, pure Ruby, out comes a deployable WAR file.
3. Glassfish server gem. (Sort of a "Pack" in the box implementation.)
Not yet. But soon.

Migrating existing Rails apps to JRuby/Rails
Be aware of the currently unsupported features.
1. Database support
- MySQL is great
- Derby & HSQL work well. Small embedable DB.
- Postgres - Few out of 1000+ tests.
- Oracle - starting to get attention
- MS SQL Server & DB - Need help, haven't really been worked on much.
Migrations mostly work well, tricky on some DBs that don't have all features.
Fixtures work well, parts of rails test. Issues generally YAML rather than DB issues.
2. Native Extentions
Option 1 - Use something else, aka don't do it.
Option 2 - Use an equivalent Java library. (binds you to jruby)
Option 3 - Port the library yourself.
Option 4 - Port by wrapping a java library.
3. Deployment Options
- Mongrel: works, but not the most efficient
- Existing WebApp Server: good concurrency, clustering, resource pooling
- Grizzly/GlassFish v3 option: lightweight, gem mongrel-like install