---
title: "Configuring CircleCI for JRuby"
description: "In this blog we discuss how to configure Circle CI for JRuby."
canonical_url: "https://www.bigbinary.com/blog/how-to-configure-circle-ci-for-jruby"
markdown_url: "https://www.bigbinary.com/blog/how-to-configure-circle-ci-for-jruby.md"
---

# Configuring CircleCI for JRuby

In this blog we discuss how to configure Circle CI for JRuby.

- Author: Ershad Kunnakkadan
- Published: August 1, 2016
- Categories: Ruby

Recently we worked with a client where we had to run a part of their
multi-threaded code in JRuby for performance reasons. They have been using
[CircleCI](https://circleci.com) with MRI for running tests. In this post I will
explain how we configured CircleCI to run the same tests using both JRuby and
MRI.

CircleCI uses `circle.yml` file for configuration. Before configuring JRuby,
this is how it looked like:

```yaml
machine:
  ruby:
    version: 2.1.5

dependencies:
  pre:
    - ./bundle_install_circle_ci.sh
  cache_directories:
    - "~/vendor/bundle"

test:
  override:
    - ? bundle exec rspec --format progress --format documentation --format
        RspecJunitFormatter --out $CIRCLE_TEST_REPORTS/app.xml
      : parallel: true
        pwd: app
        files:
          - spec/**/*_spec.rb
```

<br />
Here are the steps to enable JRuby in CircleCI.

**Specify the JDK version**

We need to specify a JDK version before using JRuby.

```yaml
machine:
  java:
    version: openjdk7
```

**Install proper dependencies**

We needed to use JRuby 9.0.4.0 but the version of JRuby that came with Ubuntu
12.04 image of CircleCI was different. We added `rvm install` command as follows
to install specific version that we wanted. Also we can configure any script
(like `bundle install`) that needs to run before running tests.

```yaml
dependencies:
  pre:
    - rvm install jruby-9.0.4.0
    - ./bundle_install_jruby_circle_ci.sh

  cache_directories:
    - "~/vendor/bundle"
```

**Configure JRuby**

We used `rvm-exec` to set JRuby for running tests for this particular component
in the `test` section. Otherwise by default it picks up MRI.

```yaml
test:
  override:
    - ? rvm-exec jruby-9.0.4.0 bash -c "bundle exec rspec --format progress
        --format documentation --format RspecJunitFormatter --out
        $CIRCLE_TEST_REPORTS/app_jruby.xml"
      : parallel: true
        pwd: app
        files:
          - spec/**/*_spec.rb
```

**Improving test runs on JRuby**

Once we started running tests with JRuby, we observed it was taking
comparatively slower to finish all tests. Most of the time was spent in starting
the JVM. We made it faster by setting
[`--dev` parameter](https://github.com/jruby/jruby/wiki/Improving-startup-time#use-the---dev-flag)
in `JRUBY_OPTS` environment variable. This parameter improves JRuby boot time
and it shaved more than a minute time for us.

```yaml
machine:
  environment:
    JRUBY_OPTS: "--dev"
```

**Here is the final circle.yml file:**

```yaml
# circle.yml

machine:
  ruby:
    version: 2.1.5

  java:
    version: openjdk7

  environment:
    JRUBY_OPTS: "--dev"

dependencies:
  pre:
    - rvm install jruby-9.0.4.0
    - ./bundle_install_jruby_circle_ci.sh

  cache_directories:
    - "~/vendor/bundle"

test:
  override:
    - ? rvm-exec jruby-9.0.4.0 bash -c "bundle exec rspec --format progress
        --format documentation --format RspecJunitFormatter --out
        $CIRCLE_TEST_REPORTS/app_jruby.xml"
      : parallel: true
        pwd: app
        files:
          - spec/**/*_spec.rb

    - ? bundle exec rspec --format progress --format documentation --format
        RspecJunitFormatter --out $CIRCLE_TEST_REPORTS/app_mri.xml
      : parallel: true
        pwd: app
        files:
          - spec/**/*_spec.rb
```

## Links

- [Human page](https://www.bigbinary.com/blog/how-to-configure-circle-ci-for-jruby)