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  • install your gem and jar dependencies into some directory /tmp/myapp
  • pack the gems + jars into gems.jar
  • pack the whole application as it into application.jar
  • run the application from these jars or put them along jruby.jar and jruby-rack.jar into WEB-INF/lib

current situation

NOTE: at the time of writing you need to use jruby-complete.jar from for the examples. jruby-mains itself work with old jruby versions.

first pack all the gem and jar dependencies into one jar:

export JARS_HOME=/tmp/app/jars
export GEM_HOME=/tmp/app
export GEM_PATH=/tmp/app
gem install bundler
bundle install

rmdir /tmp/app/doc /tmp/app/extensions /tmp/app/build_info
rm -rf /tmp/app/cache
jar -cvf gems.jar -C /tmp/app .

now pack the application:

jar -cvf application.jar .

now run these jars with

java -cp application.jar:gems.jar:jruby-complete.jar org.jruby.Main -C uri:classloader:/ -S rackup

this is equivalent to (here the classloader finds the application on the classpath ".")

java -cp .:gems.jar:jruby-complete.jar org.jruby.Main -C uri:classloader:/ -S rackup

or very close to (the current directory is on the file system and not inside the classloader)

java -cp .:gems.jar:jruby-complete.jar org.jruby.Main -C . -S rackup

the last can be reduced to (since GEM_PATH and JARS_HOME needs to be set)

java -jar jruby-complete.jar $GEM_PATH/bin/rackup

the only difference is from where the application is loaded and where the current directory (-C) is pointing to.

note: if GEM_PATH and JARS_HOME are not set then JRuby is looking for gems and jars in uri:classloader:/.

ideally bundler should be only development dependency and then can be excluded.

what about war files ?

just put the jruby-complete.jar, jruby-rack.jar, application.jar and the gems.jar into WEB-INF/lib and configure your WEB-INF/web.xml to use the classpath-layout




then the web-application uses the same loading semantic as the standalone execution.

of course you can just unpack the gems.jar and application.jar into WEB-INF/classes which does not make a difference since from both location all the ruby sources are loaded via the jruby-classloader.

using jruby-mains

this jruby-mains artifact expect the gems and jar dependencies be vendored at the root of the application.jar

JARS_HOME=./jars GEMS_HOME=. GEMS_PATH=. bundle install
jar -cvf application.jar .

and run it with

java -cp application.jar:jruby-complete.jar:jruby-mains.jar org.jruby.Main bin/rackup

or via the -S switch

java -cp application.jar:jruby-complete.jar:jruby-mains.jar org.jruby.mains.JarMain -S rackup

finally you can merge those three jar files into one and set the entry-point to org.jruby.mains.JarMain. this reduces the execution to

java -jar application-uber.jar -S rackup

some executables spawn a new ruby process which is not working from a jruby-complete exectution. but in such cases you can use the entry-point org.jruby.mains.ExtractingMain which unpacks the jar into a temporary directory and then executes the application.


use maven 3.3.x or the supplied mvnw wrappers. all integration tests in src/it are using the ruby pom DSL the pom.xml is just a dummy for the invoker plugin to find the test.


Almost all code is under the LGPL-3 license.


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request


report issues and enjoy :)


a couple of main methods for embedded (j)ruby inside a jar/war file




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