Build Tools: Maven Basics

As soon as a Java project needs external libraries, a compilation step, packaging into a JAR, and repeatable builds across machines, manually running javac and java stops scaling. Maven is a build automation and dependency management tool built around a single configuration file, pom.xml (Project Object Model), that declares what your project needs and how to build it.

Maven's core philosophy is "convention over configuration": if you follow its standard project layout and naming rules, you get a working build with very little explicit configuration. This predictability is why so many Java projects, tutorials, and onboarding guides default to Maven.

Why it matters

No real Java project is compiled by hand. A build tool downloads the libraries, compiles, runs the tests and packages the result, the same way on every machine and on the build server. Maven is the most widely used one in enterprise Java, and reading a pom.xml is a skill needed from the first day in a job.

The pom.xml Structure

Every Maven project has a pom.xml at its root describing the project's identity and dependencies.

• groupId — a reverse-domain-style identifier for the organization or project (e.g. com.webnest).
• artifactId — the name of this specific project or module (e.g. order-service).
• version — the project's version, often ending in -SNAPSHOT during active development.
• <dependencies> — the list of external libraries the project needs, each with its own groupId, artifactId, and version.
• <build> — plugin configuration controlling how compilation, testing, and packaging behave.

Dependencies and the Central Repository

Rather than manually downloading .jar files, you declare a dependency's coordinates (groupId, artifactId, version) in pom.xml, and Maven downloads it — along with any of its own transitive dependencies — from Maven Central, a shared public repository that hosts the vast majority of open-source Java libraries. Downloaded artifacts are cached locally in ~/.m2/repository, so subsequent builds (even in other projects using the same library) don't re-download it.

The Maven Build Lifecycle

Maven organizes work into a fixed sequence of phases; running a later phase automatically runs every earlier phase first. This is what makes a single command like mvn package reliably compile, test, and package in one predictable step.

• validate — checks the project structure and pom.xml are correct.
• compile — compiles the main source code (src/main/java) into target/classes.
• test — runs unit tests using a testing framework such as JUnit.
• package — bundles compiled code into a distributable format, usually a JAR or WAR, in target/.
• install — copies the packaged artifact into the local ~/.m2 repository so other local projects can depend on it.
• deploy — uploads the final artifact to a remote shared repository for other teams or environments to consume.

Example

<project xmlns="http://maven.apache.org/POM/4.0.0">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.webnest</groupId>
  <artifactId>order-service</artifactId>
  <version>1.0-SNAPSHOT</version>

  <properties>
    <maven.compiler.source>17</maven.compiler.source>
    <maven.compiler.target>17</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter</artifactId>
      <version>5.10.0</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

<!-- Terminal: mvn clean package -->

[INFO] --- compiler:compile ---
[INFO] --- surefire:test ---
[INFO] Tests run: 4, Failures: 0, Errors: 0, Skipped: 0
[INFO] --- jar:jar ---
[INFO] Building jar: target/order-service-1.0-SNAPSHOT.jar
[INFO] BUILD SUCCESS

Exercise

This exercise needs Maven installed, so it does not run in the playground. Write a minimal pom.xml for a project with the group id com.example, the artifact id demo and the version 1.0-SNAPSHOT, compiled for Java 17, with JUnit Jupiter 5.10.0 as a test-scoped dependency. Then give the command that deletes old build output, runs the tests and builds the JAR.

Expected result: the command ends with BUILD SUCCESS and creates target/demo-1.0-SNAPSHOT.jar.

<project xmlns="http://maven.apache.org/POM/4.0.0">
  <modelVersion>4.0.0</modelVersion>

  <!-- TODO: groupId, artifactId, version -->

  <!-- TODO: properties for the Java version -->

  <!-- TODO: the JUnit Jupiter dependency, test scope -->
</project>

# TODO: the command that cleans, tests and packages

<project xmlns="http://maven.apache.org/POM/4.0.0">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.example</groupId>
  <artifactId>demo</artifactId>
  <version>1.0-SNAPSHOT</version>

  <properties>
    <maven.compiler.source>17</maven.compiler.source>
    <maven.compiler.target>17</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter</artifactId>
      <version>5.10.0</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

mvn clean package

Quick quiz

Interview questions