Maven

Maven is a build automation and dependency management tool for Java projects that uses a standardized project structure and XML configurations.

Usage	Implementation	License	Current Version
CLI	Java	Apache License 2.0	3.9.11

1 Projects
- 1.1 Structure
- 1.2 Creation
2 Project Object Model
- 2.1 Dependencies
- 2.2 Plugins
3 Build Process

1 Projects

1.1 Structure

pom.xml: Configuration file for maven
src/: Contains source code
- main/: Contains application files
  - java/: Contains java packages of application
  - resources/: Contains additional files for application
- test/: Contains test files
  - java/: Contains java packages of tests
  - resources/: Contains additional files for tests
target/: Contains build files of project

1.2 Creation

Maven projects can be generated programmatically from the command-line with templates which are called archetypes:

maven-archetype-quickstart: Minimalistic maven template

# create Maven projects in current directory
mvn archetype:generate

# create Maven projects from archetype in current directory
mvn archetype:generate -DarchetypeArtifactId=maven-archetype-quickstart

2 Project Object Model

The project object model (or POM) describes the build configuration of the project in XML and is placed inside the pom.xml file in the project’s root directory.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>  <!-- POM version -->

    <groupId>com.mycompany.app</groupId>  <!-- namespace -->
    <artifactId>my-app</artifactId>       <!-- artifact name -->
    <version>1.0-SNAPSHOT</version>       <!-- artifact version -->

    <name>my-app</name>                <!-- project name -->
    <url>http://www.example.com</url>  <!-- project website -->

    <!-- build configurations -->
    <properties>
        <maven.compiler.release>25</maven.compiler.release>
        <maven.compiler.sourceEncoding>UTF-8</maven.compiler.sourceEncoding>
    </properties>

</project>

2.1 Dependencies

Dependencies installed through Maven are stored locally in the .m2 directory inside the user’s home directory. This includes downloaded dependencies and locally created Maven projects. Thereby dependencies are first looked for in the .m2 directory and are downloaded from the Maven Central when they couldn’t be found, the official online repository for Maven. The repository can be browsed via Maven Repository.

A scope is associated with every dependency that determines when, where and how it is compiled into the project to optimize performance:

compile: Used everywhere (default)
runtime: Only used on run-time
test: Only used for tests

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.mycompany.app</groupId>
    <artifactId>my-app</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>my-app</name>
    <url>http://www.example.com</url>

    <properties>
        <maven.compiler.release>21</maven.compiler.release>
        <maven.compiler.sourceEncoding>UTF-8</maven.compiler.sourceEncoding>
    </properties>

    <!-- declaring dependencies -->
    <dependencies>
        <!-- dependency declaration -->
        <dependency>
            <groupId>com.someone.app</groupId>  <!-- dependency package -->
            <artifactId>some-app</artifactId>   <!-- dependency name -->
            <version>1.0.0</version>            <!-- dependency version -->
            <scope>compile</scope>              <!-- dependency scope -->
        </dependency>

        <!-- dependency declaration -->
        <dependency>
            <groupId>com.something.app</groupId>  <!-- dependency package -->
            <artifactId>thing-app</artifactId>    <!-- dependency name -->
            <version>1.0.0</version>              <!-- dependency version -->
            <scope>test</scope>                   <!-- dependency scope -->
        </dependency>
    </dependencies>

</project> 

2.2 Plugins

Plugins add additional functionality to Maven and the build process.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.mycompany.app</groupId>
    <artifactId>my-app</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>my-app</name>
    <url>http://www.example.com</url>

    <properties>
        <maven.compiler.release>21</maven.compiler.release>
        <maven.compiler.sourceEncoding>UTF-8</maven.compiler.sourceEncoding>
    </properties>

    <!-- declaring dependencies -->
    <build>
        <plugins>
            <!-- plugn declaration -->
            <plugin>
                <groupId>org.someone.plugin</groupId>  <!-- plugin package -->
                <artifactId>some-plugin</artifactId>   <!-- plugin name -->
                <version>1.0</version>                 <!-- plugin version -->
                <!-- plugin configurations -->
                <configuration>
                    <release>25</release>
                </configuration>
            </plugin>

            <!-- plugn declaration -->
            <plugin>
                <groupId>org.something.plugin</groupId>  <!-- plugin package -->
                <artifactId>thing-plugin</artifactId>    <!-- plugin name -->
                <version>1.0</version>                   <!-- plugin version -->
                <!-- plugin configurations -->
                <configuration>
                    <release>25</release>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project> 

3 Build Process

The Maven build process comes with the following stages:

validate: Validate POM and project structure
compile: Compile project and tests
test: Execute tests
package: Bundle compiled files and resources into JAR file
verify: Verify integrity of build files
install: install bundled JAR file locally to the .m2 directory

# perform build stages
mvn validate
mvn compile   # includes validate
mvn test      # includes validate and compile
mvn package   # includes validate, compile and test
mvn verify    # includes validate, compile, test and package
mvn install   # includes validate, compile, test, package and verify

# remove build files
mvn clean
mvn clean install  # perform build stage afterwards

# perform build stage without tests
mvn install -DskipTests             # compile tests without execution
mvn install -Dmaven.test.skip=true  # no compilation or execution of tests