Maven Plugins 👷🏼‍♂️👷🏼‍♀️

https://maven.apache.org/plugins/index.html

Maven is effectively a framework that runs plugins. It just knows which plugins to run and when.

Lifecycle Plugins

maven-clean-plugin

one goal - clean
remove files generated during build process
by default removes /target directory from project root and submodule root folders

Can add the clean cycle to another lifecycle by adding the following within the project tag e.g.

This runs the clean:clean plugin goal as part of the initialize phase.

<project>
    ...
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-clean-plugin</artifactId>
                <version>3.1.0</version>
                <!-- can omit the version number - it will be inherited, but will generate a warning that it's missing -->
                <executions>
                    <execution>
                        <id>auto-clean</id>
                        <phase>initialize</phase>
                            <goals>
                            <goal>clean</goal>
                        </goals>
                    </execution>
            </plugin>
        </plugins>
    </build>
    ...
</project>

Common practice: By hooking the clean plugin into specific phases (like initialize), it can save you from having to type in clean on the command line, e.g. Instead of mvn clean package, you can now use mvn package Instead of mvn clean install, you can now use mvn install Effectively this is adding the clean plugin goal into the default lifecycle.

maven-compiler-plugin

in Default Lifecycle
two goals - compiler:compile, compiler:testCompile (and a compiler:help goal)
by default, uses the compiler 'javax.tools.JavaCompiler' - can be configured to use javac
default source and target language levels are Java 1.6, apache encourages these values to be set

Can change the compiler version in the POM.xml file.

    <properties>
    ...
        <java.version>11</java.version>
        <!-- The following two lines might also be required -->
        <maven.compiler.source>${java.version}</maven.compiler.source>
        <maven.compiler.target>${java.version}</maven.compiler.target>    ...
    </properties>

This will compile to java version 11 - changing this (e.g. to 1.6) will compile the code to a different version.

Resources Plugin

https://maven.apache.org/plugins/maven-resources-plugin/

in Default Lifecycle
3 goals - resources:resources, resources:testResources, resources:copy-resources
purpose is to copy project resources to output directory (target dir)

Resources normally live in src -> main -> resources and src -> test -> resources

resources:resources copies files in resources into target/classes ready to be packaged into a jar.

Can add an external resource directory by adding the following to POM.xml

<project>
    ...
    <build>
        <resources>
            <resource>
                <directory>[your files here]</directory>
            </resource>
        </resources>
    </build>
    ...
</project>

This overrides the default resources directory, but you can add multiple resources

<resources>
    <resource>
        <directory>resource1</directory>
    </resource>
    <resource>
        <directory>resource2</directory>
    </resource>
    <resource>
        <directory>resource3</directory>
    </resource>
</resources>

Other things this plugin can be configured for is:

specifying a character encoding scheme
filtering
including and excluding files/folders

Surefire Plugin

in Default Lifecycle
one goal: surefire:test (also surefire:help)
by default supports: JUnit3, JUnit4, JUnit5 and TestNG
by default includes classes named: Test, Test, Tests, TestCase (can change these)
also handles POJO tests

Runs tests out of your test directory. Reports are available in target/surefire-reports.

JAR Plugin

in Default Lifecycle
two goals: jar:jar, jar:test-jar
purpose - build jars from compiled artifacts and project resources
can be configured for custom manifests and to make executable jars

Adding a ClassPath entry to the Manifest

<project>
    ...
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                ...
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                        </manifest>
                    </archive>
                </configuration>
                ...
            </plugin>
        </plugins>
    </build>
    ...
    <dependencies>
        <dependency>
            <groupId>commons-lang</groupId>
            <artifactId>commons-lang</artifactId>
            <version>2.1</version>
        </dependency>
        <dependency>
            <groupId>org.codehaus.plexus</groupId>
            <artifactId>plexus-utils</artifactId>
            <version>1.1</version>
        </dependency>
    </dependencies>
    ...
</project>

This creates the following manifest

Manifest-Version: 1.0
Created-By: Apache Maven ${maven.version}
Build-Jdk: ${java.version}
Class-Path: plexus-utils-1.1.jar commons-lang-2.1.jar

Creating an Executable JAR

<project>
    ...
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                ...
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                            <mainClass>fully.qualified.MainClass</mainClass>
                        </manifest>
                    </archive>
                </configuration>
                ...
            </plugin>
        </plugins>
    </build>
    ...
</project>

Manifest-Version: 1.0
Created-By: Apache Maven ${maven.version}
Build-Jdk: ${java.version}
Main-Class: fully.qualified.MainClass
Class-Path: plexus-utils-1.1.jar commons-lang-2.1.jar

Deploy Plugin

in Default Lifecycle
two goals: deploy:deploy (deploys artifacts), deploy:deploy-file (deploys specific files)
purpose: to deploy project artifacts to remote Maven repositories
typical done in CI environments (not normally done from a developer workstation)
configuration is typically part of Maven POM - attributes for deployment are built into the POM

Maven Site Plugin

in SITE Lifecycle
7 goals
site:site - generate site for project
site:deploy - deploy site via Wagon
site:run - run site locally using Jetty as web server
site:stage - generate site to a local staging location (e.g. for testing)
site:stage-deploy - deploy site to a remote staging location
site:attach-descriptor - adds site.xml (site map file used by search engines) to files for deployment
site:jar - bundles site into a jar for deployment to a repository
site:effective-site - generates the site.xml file

Can use a variety of formats (including XML and Markdown)

Maven and Source Control

You do not need to check in the following as part of a maven project..

the target directory
*.iml file
the .idea folder

Other Plugins

Reference can be found at: maven.apache.org/ref/3.6.0/plugin-management.html