The Maven Cookbook
4.4. Creating an Ant Maven Plugin
While Maven is an improvement on Ant, Ant can still be useful when describing parts of the build process. Ant provides a set of tasks which can come in handy when you need to perform file operations or XSLT transformations or any other operation you could think of. There is a large library of available Ant tasks for everything from running JUnit tests to transforming XML to copying files to a remote server using SCP. An overview of available Ant tasks can be found online in the Apache Ant Manual. You can use these tasks as a low-level build customization language, and you can also write a Maven plugin where, instead of a Mojo written in Java, you can pass parameters to a Mojo which is an Ant build target.
To create a Maven plugin using Ant, you will need to have a
pom.xml
and a single Mojo implemented in Ant. To
get started, create a project directory named firstant-maven-plugin.
Place the following pom.xml
in this
directory.
Example 4.3. POM for an Ant Maven Plugin
<project> <modelVersion>4.0.0</modelVersion> <groupId>org.sonatype.mavenbook.plugins</groupId> <artifactId>firstant-maven-plugin</artifactId> <name>Example Ant Mojo - firstant-maven-plugin</name> <packaging>maven-plugin</packaging> <version>1.0-SNAPSHOT</version> <dependencies> <dependency> <groupId>org.apache.maven</groupId> <artifactId>maven-script-ant</artifactId> <version>3.0.5</version> </dependency> </dependencies> <build> <plugins> <plugin> <artifactId>maven-plugin-plugin</artifactId> <version>2.4</version> <dependencies> <dependency> <groupId>org.apache.maven.plugin-tools</groupId> <artifactId>maven-plugin-tools-ant</artifactId> <version>2.4</version> </dependency> </dependencies> </plugin> </plugins> </build> </project>
Next, you will need to create your Ant Mojo. An Ant mojo consists
of two parts: the Ant tasks in an XML file, and a
file which supplies Mojo descriptor information. The Ant plugin tools
are going to look for both of these files in
${basedir}/src/main/scripts
. One file will be
named echo.build.xml
and it will contain the Ant
XML.
Example 4.4. Echo Ant Mojo
<project> <target name="echotarget"> <echo>${message}</echo> </target> </project>
The other file will describe the Echo Ant Mojo and will be in the
echo.mojos.xml
file also in
${basedir}/src/main/scripts
.
Example 4.5. Echo Ant Mojo Descriptor
<pluginMetadata> <mojos> <mojo> <goal>echo</goal> <call>echotarget</call> <description>Echos a Message</description> <parameters> <parameter> <name>message</name> <property>message</property> <required>false</required> <expression>${message}</expression> <type>java.lang.Object</type> <defaultValue>Hello Maven World</defaultValue> <description>Prints a message</description> </parameter> </parameters> </mojo> </mojos> </pluginMetadata>
This echo.mojos.xml
file configures the Mojo
descriptor for this plugin. It supplies the goal name "echo", and it
tells Maven what Ant task to call in the call element. In addition to
configuring the description, this XML file configures
the message parameter to use the expression
${message}
and to have a default value of "Hello
Maven World."
If you've configured your plugin groups in
~/.m2/settings.xml
to include
org.sonatype.mavenbook.plugins
, you can install this
Ant plugin by executing the following command at the
command-line:
$ mvn install
[INFO] ------------------------------------------------------------------------
[INFO] Building Example Ant Mojo - firstant-maven-plugin
[INFO] task-segment: [install]
[INFO] ------------------------------------------------------------------------
[INFO] [plugin:descriptor]
[INFO] Using 3 extractors.
[INFO] Applying extractor for language: java
[INFO] Extractor for language: java found 0 mojo descriptors.
[INFO] Applying extractor for language: bsh
[INFO] Extractor for language: bsh found 0 mojo descriptors.
[INFO] Applying extractor for language: ant
[INFO] Extractor for language: ant found 1 mojo descriptors.
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
Note that the plugin:descriptor
goal found a
single Ant mojo descriptor. To run this goal, you would execute the
following command-line:
$ mvn firstant:echo
...
[INFO] [firstant:echo]
echotarget:
[echo] Hello Maven World
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
The echo
goal executed and printed out the
default value of the message
parameter. If you are
used to Apache Ant build scripts, you will notice that Ant prints out
the name of the target executed and then adds a logging prefix to the
output of the echo Ant task.
While Maven is an improvement on Ant, Ant can still be useful when describing parts of the build process. Ant provides a set of tasks which can come in handy when you need to perform file operations or XSLT transformations or any other operation you could think of. There is a large library of available Ant tasks for everything from running JUnit tests to transforming XML to copying files to a remote server using SCP. An overview of available Ant tasks can be found online in the Apache Ant Manual. You can use these tasks as a low-level build customization language, and you can also write a Maven plugin where, instead of a Mojo written in Java, you can pass parameters to a Mojo which is an Ant build target.