The Build Lifecycle

4.1. Introduction

Maven models projects as nouns which are described by a POM. The POM captures the identity of a project: What does a project contain? What type of packaging a project needs? Does the project have a parent? What are the dependencies? We’ve explored the idea of describing a project in the previous chapters, but we haven’t introduced the mechanism that allows Maven to act upon these objects. In Maven the "verbs" are goals packaged in Maven plugins which are tied to a phases in a build lifecycle. A Maven lifecycle consists of a sequence of named phases: prepare-resources, compile, package, and install among other. There is phase that captures compilation and a phase that captures packaging. There are pre- and post- phases which can be used to register goals which must run prior to compilation, or tasks which must be run after a particular phase. When you tell Maven to build a project, you are telling Maven to step through a defined sequence of phases and execute any goals which may have been registered with each phase.

A build lifecycle is an organized sequence of phases that exist to give order to a set of goals. Those goals are chosen and bound by the packaging type of the project being acted upon. There are three standard lifecycles in Maven: clean, default (sometimes called build) and site. In this chapter, you are going to learn how Maven ties goals to lifecycle phases and how the lifecycle can be customized. You will also learn about the default lifecycle phases.

4.1.1. Clean Lifecycle (clean)

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:

• pre-clean
• clean
• post-clean

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.

Triggering a Goal on pre-clean.

<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>

Running mvn clean on a project with this build configuration will produce output similar to the following:

[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.

Customizing Behavior of the Clean Plugin.

<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>

4.1.2. Default Lifecycle (default)

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 4.1, “Maven Lifecycle Phases”.

Table 4.1. Maven Lifecycle Phases

4.1.3. Site Lifecycle (site)

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:

1. pre-site
2. site
3. post-site
4. site-deploy

The default goals bound to the site lifecycle is:

1. site - site:site
2. site-deploy -site:deploy

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

4.2. Package-specific Lifecycles

The specific goals bound to each phase default to a set of goals specific to a project’s packaging. A project with packaging jar has a different set of default goals from a project with a packaging of war. The packaging element affects the steps required to build a project. For an example of how the packaging affects the build, consider two projects: one with pom packaging and the other with jar packaging. The project with pom packaging will run the site:attach-descriptor goal during the package phase, and the project with jar packaging will run the jar:jar goal instead.

4.2.1. JAR

JAR is the default packaging type, the most common, and thus the most commonly encountered lifecycle configuration. The default goals for the JAR lifecycle are shown in Table 4.2, “Default Goals for JAR Packaging”.

Table 4.2. Default Goals for JAR Packaging

4.2.2. POM

POM is the simplest packaging type. The artifact that it generates is itself only, rather than a JAR, SAR, or EAR. There is no code to test or compile, and there are no resources the process. The default goals for projects with POM packaging are shown in Table 4.3, “Default Goals for POM Packaging”.

Table 4.3. Default Goals for POM Packaging

4.2.3. Maven Plugin

This packaging type is similar to JAR packaging type with three additions: plugin:descriptor, plugin:addPluginArtifactMetadata, and plugin:updateRegistry. These goals generate a descriptor file and perform some modifications to the repository data. The default goals for projects with plugin packaging are shown in Table 4.4, “Default Goals for Plugin Packaging”.

Table 4.4. Default Goals for Plugin Packaging

4.2.4. EJB

EJBs, or Enterprise Java Beans, are a common data access mechanism for model-driven development in Enterprise Java. Maven provides support for EJB 2 and 3. Though you must configure the EJB plugin to specifically package for EJB3, else the plugin defaults to 2.1 and looks for the presence of certain EJB configuration files. The default goals for projects with EJB packaging are shown in Table 4.5, “Default Goals for EJB Packaging”.

Table 4.5. Default Goals for EJB Packaging

4.2.5. WAR

The WAR packaging type is similar to the JAR and EJB types. The exception being the package goal of war:war. Note that the war:war goal requires a web.xml configuration in your src/main/webapp/WEB-INF directory. The default goals for projects with WAR packaging are shown in Table 4.6, “Default Goals for WAR Packaging”.

Table 4.6. Default Goals for WAR Packaging

4.2.6. EAR

EARs are probably the simplest Java EE constructs, consisting primarily of the deployment descriptor application.xml file, some resources and some modules. The EAR plugin has a goal named generate-application-xml which generates the application.xml based upon the configuration in the EAR project’s POM. The default goals for projects with EAR packaging are shown in Table 4.7, “Default Goals for EAR Packaging”.

Table 4.7. Default Goals for EAR Packaging

4.2.7. Other Packaging Types

This is not an exhaustive list of every packaging type available for Maven. There are a number of packaging formats available through external projects and plugins: the NAR (native archive) packaging type, the SWF and SWC packaging types for projects that produce Adobe Flash and Flex content, and many others. You can also define a custom packaging type and customize the default lifecycle goals to suit your own project packaging requirements.

4.3. Common Lifecycle Goals

Many of the packaging lifecycles have similar goals. If you look at the goals bound to the WAR and JAR lifecycles, you’ll see that they differ only in the package phase. The package phase of the WAR lifecycle calls war:war and the package phase of the JAR lifecycle calls jar:jar. Most of the lifecycles you will come into contact with share some common lifecycle goals for managing resources, running tests, and compiling source code. In this section, we’ll explore some of these common lifecycle goals in detail.

4.3.1. Process Resources

The process-resources phase "processes" resources and copies them to the output directory. If you haven’t customized the default directory locations defined in the Super POM, this means that Maven will copy the files from ${basedir}/src/main/resources to ${basedir}/target/classes or the directory defined in ${project.build.outputDirectory}.

Using Properties in Project Resources.

<service>
    <!-- This URL was set by project version ${project.version} -->
    <url>${jdbc.url}</url>
    <user>${jdbc.username}</user>
    <password>${jdbc.password}</password>
</service>

4.3.2. Compile

Most lifecycles bind the Compiler plugin’s compile goal to the compile phase. This phase calls out to compile:compile which is configured to compile all of the source code and copy the bytecode to the build output directory.

4.3.3. Process Test Resources

The process-test-resources phase is almost indistinguishable from the process-resources phase. There are some trivial differences in the POM, but most everything the same.

4.3.4. Test Compile

The test-compile phase is almost identical to the compile phase. The only difference is that test-compile is going to invoke compile:testCompile to compile source from the test source directory to the test build output directory.

4.3.5. Test

Most lifecycles bind the test goal of the Surefire plugin to the test phase. The Surefire plugin is Maven’s unit testing plugin, the default behavior of Surefire is to look for all classes ending in *Test in the test source directory and to run them as unit tests.

4.3.6. Install

The install goal of the Install plugin is almost always bound to the install lifecycle phase. This install:install goal simply installs a project’s main artifact to the local repository.

4.3.7. Deploy

The deploy goal of the Deploy plugin is usually bound to the deploy lifecycle phase. This phase is used to deploy an artifact to a remote Maven repository, this is usually required to update a remote repository when you are performing a release.