Quokka supports multiple project builds by leveraging the subant task from Ant. This can be combined with the built-in buildpath task to automatically discover sub-projects and calculate a build sequence, taking into account interdependencies.

When building multiple projects, there is commonly a parent project that is used to build all of the modules as a single unit. Quokka does not attempt to impose special relationships between parents and children, especially with regard to targets. i.e. it is up to the user to decide what child modules to build and what targets are available on those particular children.

There are a few features to allow parent/child integration:

Apart from facilitating the building of multiple projects as a single unit, the other major use of parent projects is to aggregate reports such as unit testing and code coverage to get an overall picture of the project. The jUnit, Cobertura, JavaDoc and Help plugins all support aggregation.

The following is an example of a multiple project build taken from the quokka.archetype.multiproject archetype. The archetype consists of the following modules:

Below is the parent build.xml used to build the modules:

<project name="master">
    <!-- Code modules in sequence allowing for inter-dependencies -->
    <path id="buildpath-code" path="modules/util:modules/server:modules/client"/>

    <!-- All modules -->
    <path id="buildpath">
        <path path="modules/depset"/>
        <path refid="buildpath-code"/>
    </path>

    <!-- A macro to run a target on all child modules and optionally the master -->
    <macrodef name="iterate">
        <attribute name="target"/>
        <attribute name="master" default="none"/>
        <attribute name="buildpathref" default="buildpath"/>
        <sequential>
            <subant target="@{target}" buildpathref="@{buildpathref}" 
                    antfile="build-quokka.xml"/>
            <if>
                <not><equals arg1="@{master}" arg2="none"/></not>
                <then>
                    <run-target target="@{master}"/>
                </then>
            </if>
        </sequential>
    </macrodef>

    <target name="install-all" description="Install all modules">
        <iterate target="install"/>
    </target>

    <target name="clean-all" description="Cleans all modules">
        <iterate target="clean" master="clean"/>
    </target>

    <!-- This is an example of building an individual report for all modules in isolation
         Note: By using the collect target on the child modules, it skips the
               report generation at lower levels, only collecting the data -->
    <target name="cobertura-all" description="Runs the cobertura report for all modules">
        <iterate target="cobertura:collect" master="cobertura:aggregate-report"
                 buildpathref="buildpath-code"/>
    </target>

    <target name="reports-all" 
            description="Runs the dev reports for all modules and aggregates results">
        <iterate target="devreport:generate" master="devreport:reports"/>
    </target>
</project>

As you can see, the above file is as standard Ant build file, using mostly standard Ant tasks. This provides a great deal of flexibility for the interaction between parents and children. For example, multiple build paths are defined, one for all modules and one for code modules, allowing subsets of modules to be handled differently.

The above example does use several bundled tasks from the ant-contrib library, notably the if and run-target tasks. run-target is important as it allows the build file to execute targets on the same project instance (unlike ant-call). This allows it to find report data stored on the parent instance by child modules. See Built-in Ant Extensions for more information on what additional built-in tasks are available.

To complete the picture, here is the parent build-quokka.xml file:

...
<project name="master" default-target="install-all">
    <dependency-set>
        <!-- Clean target directory -->
        <plugin group="quokka.plugin.standard-lifecycle" version="0.3"
            use-defaults="false" targets="clean"/>

        <!-- Aggregated development reports -->
        <plugin group="quokka.plugin.devreport" version="0.3"/>

        <plugin group="quokka.plugin.cobertura" version="0.3"
                use-defaults="false" targets="aggregate-report"/>

        <plugin group="quokka.plugin.junitreport" version="0.3"
                use-defaults="false" targets="aggregate-report"/>

        <plugin group="quokka.plugin.help" version="0.3"
                use-defaults="false" targets="aggregate-report, help"/>

        <plugin group="quokka.plugin.devreport" version="0.3"
                use-defaults="false" targets="reports"/>
    </dependency-set>
</project>

It includes the clean plugin and various aggregated reports.