Calls a given target for all defined sub-builds. This is an extension of ant for bulk project execution. This task must not be used outside of a target if it invokes the same build file it is part of.

Since Apache Ant 1.6

subant uses ant internally so many things said in ant's manual page apply here as well.

Use with directories

subant can be used with directory sets to execute a build from different directories. 2 different options are offered : to run the same build file /somepath/otherpath/mybuild.xml with different base directories, use the genericantfile attribute if you want to run directory1/mybuild.xml, directory2/mybuild.xml, ...., use the antfile attribute. The subant task does not set the base directory for you in this case, because you can specify it in each build file.

Attribute	Description	Type	Requirement
antfile	Build file name, to use in conjunction with directories. Defaults to "build.xml". If genericantfile is set, this attribute is ignored.	String	Optional
buildpath	Set the buildpath to be used to find sub-projects.	Path
buildpathref	Buildpath to use, by reference.	Reference
failonerror	Sets whether to fail with a build exception on error, or go on.	boolean
genericantfile	Build file path, to use in conjunction with directories. Use genericantfile, in order to run the same build file with different basedirs. If this attribute is set, antfile is ignored.	File
inheritall	Corresponds to <ant>'s inheritall attribute but defaults to false in this task..	boolean
inheritrefs	Corresponds to <ant>'s inheritrefs attribute.	boolean
output	Corresponds to <ant>'s output attribute.	String
target		String
verbose	Enable/ disable log messages showing when each sub-build path is entered/ exited. The default value is false.	boolean

any filesystem based resource collection

This includes <fileset>, <dirset> and <filelist> which are the nested resource collections supported prior to Ant 1.7.

dirset (org.apache.tools.ant.types.DirSet)

Adds a directory set to the implicit build path. Note that the directories will be added to the build path in no particular order, so if order is significant, one should use a file list instead!

filelist (org.apache.tools.ant.types.FileList)

Adds an ordered file list to the implicit build path. Note that contrary to file and directory sets, file lists can reference non-existent files or directories!

fileset (org.apache.tools.ant.types.FileSet)

Adds a file set to the implicit build path. Note that the directories will be added to the build path in no particular order, so if order is significant, one should use a file list instead!

property (org.apache.tools.ant.taskdefs.Property)

Corresponds to <ant>'s nested <property> element. When more than one nested <property> element would set a property of the same name, the one declared last will win. This is for backwards compatibility reasons even so it is different from the way <property> tasks in build files behave.

propertyset (org.apache.tools.ant.types.PropertySet)

Corresponds to <ant>'s nested <propertyset> element.

buildpath (org.apache.tools.ant.types.Path)

Creates a nested build path, and add it to the implicit build path.

buildpathelement (org.apache.tools.ant.types.Path.PathElement)

Creates a nested <buildpathelement>, and add it to the implicit build path.

target (org.apache.tools.ant.taskdefs.Ant.TargetElement)

You can specify multiple targets using nested <target> elements instead of using the target attribute. These will be executed as if Ant had been invoked with a single target whose dependencies are the targets so specified, in the order specified. Attribute Description Required name The name of the called target. Yes since Ant 1.7.

        <project name="subant" default="subant1">
            <property name="build.dir" value="subant.build"/>
            <target name="subant1">
                <subant target="">
                    <property name="build.dir" value="subant1.build"/>
                    <property name="not.overloaded" value="not.overloaded"/>
                    <fileset dir="." includes="*/build.xml"/>
                </subant>
            </target>
        </project>
        

this snippet build file will run ant in each subdirectory of the project directory, where a file called build.xml can be found. The property build.dir will have the value subant1.build in the ant projects called by subant.

          <subant target="">
              <propertyset>
                  <propertyref prefix="toplevel"/>
                  <mapper type="glob" from="foo*" to="bar*"/>
              </propertyset>
              <fileset dir="." includes="*/build.xml"/>
          </subant>
        

this snippet build file will run ant in each subdirectory of the project directory, where a file called build.xml can be found. All properties whose name starts with "foo" are passed, their names are changed to start with "bar" instead

          <subant target="compile" genericantfile="/opt/project/build1.xml">
              <dirset dir="." includes="projects*"/>
          </subant>
        

assuming the subdirs of the project dir are called projects1, projects2, projects3 this snippet will execute the compile target of /opt/project/build1.xml, setting the basedir to projects1, projects2, projects3

Now a little more complex - but useful - scenario. Assume that we have a directory structure like this:

        root
          |  common.xml
          |  build.xml
          |
          +-- modules
                +-- modA
                |     +-- src
                +-- modB
                      +-- src

        common.xml:

        <project>
            <property name="src.dir"      value="src"/>
            <property name="build.dir"    value="build"/>
            <property name="classes.dir"  value="${build.dir}/classes"/>

            <target name="compile">
                <mkdir dir="${classes.dir}"/>
                <javac srcdir="${src.dir}" destdir="${classes.dir}"/>
            </target>

            <!-- more targets -->
        </project>

        build.xml:

        <project>

            <macrodef name="iterate">
                <attribute name="target"/>
                <sequential>
                    <subant target="@{target}">
                        <fileset dir="modules" includes="*/build.xml"/>
                    </subant>
                </sequential>
            </macrodef>


            <target name="compile">
                <iterate target="compile"/>
            </target>

            <!-- more targets -->
        </project>

        modules/modA/build.xml:

        <project name="modA">
            <import file="../../common.xml"/>
        </project>
        

This results in very small buildfiles in the modules, maintainable buildfile (common.xml) and a clear project structure. Additionally the root buildfile is capable to run the whole build over all modules.

        <subant failonerror="false">
            <fileset dir="." includes="**/build.xml" excludes="build.xml"/>
            <target name="clean"/>
            <target name="build"/>
        </subant>
        

Does a "clean build" for each subproject.

Hint: because buildfiles are plain xml, you could generate the masterbuildfile from the common buildfile by using a XSLT transformation:

        <xslt in="common.xml"
              out="master.xml"
              style="${ant.home}/etc/common2master.xsl"
        />