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Building JRuby from Source


JRuby uses Maven for building and bootstrapping itself, along with Rake, RSpec, and MSpec for running integration tests.

Building Commandline JRuby

The first time you enter a new source dump of JRuby (from a src zip or from a git clone), you need to build the lib/jruby.jar. The command to execute is:


This will run the default "install" goal (mvn install) and will do all of the following:

  • Compile JRuby
  • Build lib/jruby.jar, needed for running at command line
  • It will install the default gems specifications lib/ruby/gems/shared/specifications/default/ and the ruby files of those gems in lib/ruby/stdlib/.

The environment is now suitable for running Ruby applications.

Running JRuby

Note: RVM users must first run:

rvm use system

to make sure you do not use another Ruby's gems or execute another Ruby implementation.

After building lib/jruby.jar, JRuby can be run with the bin/jruby executable. If the jruby-launcher gem installed successfully, this will be a native executable for your platform; otherwise, it will be a copy of the bin/jruby.bash bash script.

RubyGems is installed by default, and available in bin/gem. It will attempt to locate the jruby executable using /usr/bin/env, so you will need the bin dir in your PATH environment or you will need to call it via JRuby using jruby -S gem ....

The -S flag will run any script installed in JRuby's bin dir by RubyGems. This can be a simple way to ensure you're running the JRuby (or Ruby) version you think you are.

Developing and Testing

JRuby employs a large suite of tests, so there are many ways you can verify that JRuby is still fully functional.

Hacking the Build System

for a general overview of the different directories and maven artifacts see JRuby Build

For this only the pom.rb needs to edited. using mvn-3.3.x or the maven wrapper ./mvnw will generate the pom.xml file where needed. For the jar files of the build those pom.xml will be generated for some use-cases, i.e. some IDEs need them.

To regenerate the pom.xml just run ./mvnw which will create them.

Setup Testing

In order to prepare JRuby for testing, you must bootstrap the dev environment. This will do the following:

  • Install rspec, rake, minitest, minitest-excludes, and dependencies needed to run integration tests.
mvn -Pbootstrap

In case there is a problem with installing the jruby-launcher (due to missing compiler or so) use

mvn -Pbootstrap-no-launcher

This only needs to be run once to install these gems or if you update one of the gems to a newer version or clean out all installed gems.

Incremental compiling

After changing Java code, you can recompile quickly by running one of the jar files by

mvn -pl core

Day to Day Testing

For normal day-to-day testing, we recommend running the Ruby specs. We have set aside a "fast" grouping that takes only a couple minutes to run:

jruby -S rake spec:ruby:fast

For a more intensive workout, you can also run the Ruby (MRI) tests via the following rake command:

jruby -S rake test:mri

This suite takes a while to complete, so if you want to run an individual file from MRI's tests (under test/mri), use one of the following commands:

Run a specific test from the MRI suite

The MRI suite (under test/mri) has a runner script in test/mri/runner.rb that sets up an appropriate test environment. Many of the MRI tests will need to be run via this script.

jruby test/mri/runner.rb test/mri/<path to test>

You can pass -v to the runner for verbose output or -n test_method_name to only run a single test method.

Run a test file with known-failing tests excluded

The runner script provides a mechanism for "excluding" known failing tests. These are usually features that JRuby has not yet implemented or can't implement on the JVM.

Excludes are in the form of Ruby scripts under test/mri/exclude, named based on the name of the test case's class, exclude with comment tests known to fail.

To run a given test with these excludes enabled, you can use the --excludes flag:

bin/jruby test/mri/runner.rb --excludes=test/mri/excludes <test file>

Run a single Ruby spec

Individual specs can be run with the mspec tool:

jruby spec/mspec/bin/mspec ci spec/ruby/<path to spec>

If ci is omitted or replaced with run you will see any specs known to fail. The ci command avoids running those specs.

Run JRuby with remote debugging

If you are familiar with Java debuggers, you can attach one to a JRuby process using the JDWP agent. The exact flag may vary with debugger and platform:

bin/jruby -T-J-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=5005 <rest of arguments>

JRuby internal unit tests

If you are making changes that would affect JRuby's core runtime or embedding APIs, you should run JRuby's Java-based unit tests via

mvn -Ptest

Tests for other ways of deploying and packaging JRuby

There are some maven integration tests (i.e. consistency test if all gems are included, osgi test, etc) for the various distributions of JRuby which can be invoked with

mvn -Pmain -Dinvoker.skip=false
mvn -Pcomplete -Dinvoker.skip=false
mvn -Pdist -Dinvoker.skip=false

Just Like CI

JRuby runs CI tests on TravisCI. See .travis.yml.

Maven integration tests - -Pjruby-complete or -Pmain

maven integration tests will use the packed maven artifact to run the tests in a forked maven instance. These maven projects are locatated in


To trigger the tests with the build:

mvn -Pmain -Dinvoker.skip=false
mvn -Pcomplete -Dinvoker.skip=false
mvn -Pdist -Dinvoker.skip=false
mvn -Pjruby-jars -Dinvoker.skip=false

To pick a particular test, add the name of the directory inside the respective src/it folder, like (wildcards are possible):

mvn -Pmain -Dinvoker.skip=false -Dinvoker.test=integrity
mvn -Pmain -Dinvoker.skip=false -Dinvoker.test=j2ee*
mvn -Pmain -Dinvoker.skip=false -Dinvoker.test=osgi*

Clean Build

To clean the build it is important to use the same profile for the clean as what you want to build. The best way to clean build something is, i.e. jruby-jars

mvn clean install -Pjruby-jars

This first cleans everything and then starts the new build in one go!

Cleaning the build may be necessary after switching to a different version of JRuby (for example, after switching git branches) to ensure that everything is rebuilt properly.

NOTE: mvn clean just cleans the jruby-core artifact and the ./lib/jruby.jar!

Clean everything:

mvn -Pclean

Distribution Packages

All distribution packages need maven-3.3.x or the use of supplied maven wrapper. All examples below will show the use of the maven wrapper.

The tar.gz and zip distribution packages

./mvnw -Pdist

The files will be in ./maven/jruby-dist/target.


./mvnw -Pcomplete

The file will be in ./maven/jruby-complete/target.

jruby maven artifacts

./mvnw -Pmain

And those files will be installed in your maven local-repository ready to use with maven, ivy, buildr, etc.

jruby jars gem

./mvnw -Pjruby-jars

The gem will be in ./maven/jruby-jars/pkg.

Building ALL packages

./mvnw -Pall

Cleaning the build

This will also clean the ext directories, i.e. a new build will then use the latest code from there for lib/ruby.

./mvnw -Pclean


First set the new version in the file VERSION inside the root directory and then to deploy the maven artifact to sonatype oss execute:

./mvnw clean deploy -Psonatype-oss-release

Go to and close the deployment, which will check if all 'required' files are in place and then finally push the release to Maven Central and . . .

Start a new version

After the release, set the new development version in VERSION and generate the pom.xml files: