Liz Douglass

Things I like about Buildr

with 3 comments

A few months ago the idea of myself writing such words (“Things I like about Buildr“) seemed very unlikely and I dare say that my project buddies may be surprised at the statement. Buildr, for those unfamiliar, is a build tool for Java applications that is written in Ruby. It’s key benefit is its concise and extensible nature. A bit of the wow factor of Buildr is a bit lost on me because I’ve not yet used Maven and I’ve only used Ant in some pretty straightforward ways… and I’d not used Rake prior to using Buildr. (So a strong starting point I’m sure you’d agree. Hhhmm, anyway…)

Our project buildfile started off looking very much like the example in the Buildr documentation, but has since grown significantly in functionality but not proportionally in size. We have complimented the Buildr functionality with handfuls of Rake tasks that perform other bits and pieces associated with our build, such as:

  • Deploying a WAR package to a Tomcat server
  • Starting and stopping database and Selenium servers
  • Updating and rolling back our HSQLDB and Oracle databases using LiquiBase
  • Checking the contents of the build artifacts produced using the Buildr check functionality

The time we’ve spent trawling through the documentation and getting ankle deep in the source has paid off. I want to capture how we’ve set up some of these build activities. So without further introduction and in no particular order, here are some of my favourites (drumroll):

1. Pretty packaging

In my earlier post I described how we used One-JAR to create a single JAR containing all the bits required to update/rollback a database using LiquiBase. Below is the sub-project task that is used to package the lot. The nicest things about this sub-project are how easily we’ve packaged the included JARs, and how easily we’ve added entries into the manifest file:

        define "assembly" do
            package(:jar).path("lib").tap do | p |
                p.include artifact(LIQUIBASE_JAR).to_s
                p.include artifact(HSQLDB_CLIENT_JAR).to_s
            package(:jar).path("main").tap do | p |
                p.include project('database-migration').package(:jar)
            package(:jar).include file('../changelog.xml')
            package(:jar).with :manifest=>manifest.merge(

2. Delightful dependencies

Some of our rake tasks require us to depend on the existence of a WAR or JAR that has been packaged in one of our buildfile sub-projects. For example, the task that deploys to a Tomcat server depends on a WAR file being generated from one of our sub-projects. Thanks to Buildr, you can do something like this:

task :foo => ['rake:MyProject:MySubProject:package'] do

Note that it is also possible and extemely easy to refer to an artifact that one of your projects has created by using syntax like this:


3. Fabulous filtering

We are using HSQLDB for development because it’s really light. Our application also needs to support Oracle though, and hence we wanted to run some of our acceptance tests using both databases. To achieve this we created another Buildr sub-project that runs some of the tests against Oracle (we already had the one that runs all the acceptance tests with HSQLDB). There are two things about this sub-project (below) that impress me. The first is that we reuse code using Buildr’s filter task. The second is how easily we can run only a subset of the tests using ‘test.include’:

            define 'my-sub-project' do
                test.compile.with _('target/classes')
                test.using :properties => { :my_property => property_value }
                test.include '*only_these_tests*'

4. Cheeky checking

Buildr callbacks can be used to extend projects. We’ve combined the after-define callback with the handy project check task to test that we’ve built what we expect to and created a number of modules like this one:

module CheckJarExists
    include Extension

    after_define do |project|
        project.enhance do
            project.check_jar_exists project

    def check_jar_exists project
        project.check project.package(:jar), 'should exist' do
            puts 'checking jar package exists....'
            it.should exist

And just in-case you’re like me and unsure of how to include this module in a project task, here’s how we did it:

define "subproject" do
      extend CheckJarExists

I’m sure there’s lots more favourites out there in the deep blue Buildr sea… happy fishing!


Written by lizdouglass

December 20, 2008 at 11:34 pm

Posted in Building, JARs, Java, Ruby

Tagged with , , , , , ,

3 Responses

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  1. 2. ….
    task :foo => [‘rake:MyProject:MySubProject:package’] do

    you can use:
    task :foo => project(‘MySubProject’).packages
    task :foo => project(‘MySubProject’).task(‘package’)
    task :foo => project(‘MySubProject’).package(:jar)

    a. it makes sure MySubProject has already been evaluated (in your case, the fact the task ‘MyProject:MySubProject:package’ exists is a coincidence)
    b. in the third alternative, you make the dependency explicit on the package you need only.


    here you run the filter (copying files and filtering them) when the project is defined, and not when tasks are executing. this means that even if you want to execute just a specific task (e.g. buildr MyProject:MySubProject:package), the filter (in another project) will execute.

    instead, wrap this in a task and make ‘compile’ depend on it

    also, not sure why you want to copy the files (why not: compile.from(project(‘bar’).compile.sources)?), or why use filter (which is when you want to change properties in the file) and not ‘cp project(‘bar’).compile.sources _(‘my_directory_1′)’


    in check_jar_exists, the call to project.package(:jar) creates a jar packaging task on the project. what if one day you will have a project without jar package?
    instead:{|p|p.type == :jar} (and do nothing if the returned list is empty)

    or maybe you’re only including in projects that have a jar? in this case, add
    class Buildr::Project
    include CheckJarExists
    at the end of the check_jar_exists.rb file and then it will do the checks for all projects, but only those that have a jar


    December 26, 2008 at 1:46 pm

  2. Thanks for your feedback ittayd. Please note that the comment about point 2 assumes that we are inside the Buildr namespace.


    January 5, 2009 at 10:00 am

  3. […] Interesting to read an old post from 2008 in which Liz Douglas stretch Buildr to the point that it becomes almost a continuous integration tool: […]

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