Maven: The Definitive Guide

The first lifecycle you'll be interested in is the simplest lifecycle in Maven. Running mvn clean invokes the clean lifecycle which consists of three lifecycle phases:

The interesting phase in the clean lifecycle is the clean phase. The Clean plugin's clean goal (clean:clean) is bound to the clean phase in the clean lifecycle. The clean:clean goal deletes the output of a build by deleting the build directory. If you haven't customized the location of the build directory it will be the ${basedir}/target directory as defined by the Super POM. When you execute the clean:clean goal you do not do so by executing the goal directly with mvn clean:clean, you do so by executing the clean phase of the clean lifecycle. Executing the clean phase gives Maven an opportunity to execute any other goals which may be bound to the pre-clean phase.

For example, suppose you wanted to trigger an antrun:run goal task to echo a notification on pre-clean, or to make an archive of a project's build directory before it is deleted. Simply running the clean:clean goal will not execute the lifecycle at all, but specifying the clean phase will use the clean lifecycle and advance through the three lifecycle phases until it reaches the clean phase. Example 10.1, “Triggering a Goal on pre-clean” shows an example of build configuration which binds the antrun:run goal to the pre-clean phase to echo an alert that the project artifact is about to be deleted. In this example, the antrun:run goal is being used to execute some arbitrary Ant commands to check for an existing project artifact. If the project's artifact is about to be deleted it will print this to the screen

<project>
  ...
  <build>
    <plugins>... <plugin>
    <artifactId>maven-antrun-plugin</artifactId>
    <executions>
      <execution>
        <id>file-exists</id>
        <phase>pre-clean</phase>
        <goals>
          <goal>run</goal>
        </goals>
        <configuration>
          <tasks>
            <!-- adds the ant-contrib tasks (if/then/else used below) -->
            <taskdef resource="net/sf/antcontrib/antcontrib.properties" />
            <available 
              file="${project.build.directory}/${project.build.finalName}.${project.packaging}"
              property="file.exists" value="true" />

            <if>
              <not>
                <isset property="file.exists" />
              </not>
              <then>
                <echo>No
                  ${project.build.finalName}.${project.packaging} to
                  delete</echo>
              </then>
              <else>
                <echo>Deleting
                  ${project.build.finalName}.${project.packaging}</echo>
              </else>
            </if>
          </tasks>
        </configuration>
      </execution>
    </executions>
    <dependencies>
      <dependency>
        <groupId>ant-contrib</groupId>
        <artifactId>ant-contrib</artifactId>
        <version>1.0b2</version>
      </dependency>
    </dependencies>
  </plugin>
  </plugins>
  </build> 
</project>

[INFO] Scanning for projects...
[INFO] ----------------------------------------------------------------------
[INFO] Building Your Project
[INFO]    task-segment: [clean]
[INFO] ----------------------------------------------------------------------
[INFO] [antrun:run {execution: file-exists}]
[INFO] Executing tasks
     [echo] Deleting your-project-1.0-SNAPSHOT.jar
[INFO] Executed tasks
[INFO] [clean:clean]
[INFO] Deleting directory ~/corp/your-project/target
[INFO] Deleting directory ~/corp/your-project/target/classes
[INFO] Deleting directory ~/corp/your-project/target/test-classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1 second
[INFO] Finished at: Wed Nov 08 11:46:26 CST 2006
[INFO] Final Memory: 2M/5M
[INFO] ------------------------------------------------------------------------

In addition to configuring Maven to run a goal during the pre-clean phase, you can also customize the Clean plugin to delete files in addition to the build output directory. You can configure the plugin to remove specific files in a fileSet. The example below configures clean to remove all .class files in a directory named target-other/ using standard Ant file wildcards: * and **.

<project>
  <modelVersion>4.0.0</modelVersion>
  ...
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-clean-plugin</artifactId>
        <configuration>
          <filesets>
            <fileset>
              <directory>target-other</directory>
              <includes>
                <include>*.class</include>
              </includes>
            </fileset>
          </filesets>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Most Maven users will be familiar with the default lifecycle. It is a general model of a build process for a software application. The first phase is validate and the last phase is deploy. The phases in the default Maven lifecycle are shown in Table 10.1, “Maven Lifecycle Phases”.

Maven does more than build software artifacts from project, it can also generate project documentation and reports about the project, or a collection of projects. Project documentation and site generation have a dedicated lifecycle which contains four phases:

The default goals bound to the site lifecycle is:

The packaging type does not usually alter this lifecycle since packaging types are concerned primarily with artifact creation, not with the type of site generated. The Site plugin kicks off the execution of Doxia document generation and other report generation plugins. You can generate a site from a Maven project by running the following command:

$ mvn site

For more information about Maven Site generation, see Chapter 15, Site Generation.