In this chapter, you will explore the most essential Maven command-line interface (CLI) commands every beginner should know. These commands help you manage your Java projects efficiently, automate common development tasks, and ensure your builds are clean and reproducible.

You will learn about the following commands:

• mvn clean: Remove all files generated by the previous build;
• mvn compile: Compile your project's source code;
• mvn test: Run your project's unit tests using JUnit Jupiter;
• mvn package: Package your compiled code into a distributable format, such as a JAR file.

Each command will be explained with clear descriptions and hands-on examples. By the end of this chapter, you will be comfortable running these commands to build, test, and package your own Java projects using Maven.

Understanding mvn clean

The mvn clean command is used to clean your Maven project by removing all files generated by previous builds. Specifically, it deletes the target directory, which contains compiled classes, packaged JAR files, and other build outputs. This helps ensure that your next build starts from a clean state, avoiding issues caused by outdated or leftover files.

When you run mvn clean, Maven triggers the clean phase of the build lifecycle. This phase is responsible for cleaning up the project before a new build.

Terminal Example

mvn clean

After running this command, the target directory and its contents will be deleted from your project folder. This prepares your project for a fresh build.

The mvn compile Command

The mvn compile command compiles your project's source code. When you run this command, Maven processes all Java files in the src/main/java directory and generates .class files in the target/classes directory.

This command triggers the compile phase of the Maven build lifecycle. The compile phase is responsible for transforming your source code into bytecode that the Java Virtual Machine can execute.

Example: Running mvn compile

To compile your project, open a terminal in your project's root directory and run:

mvn compile

After running this command, check the target/classes directory for the compiled .class files. This confirms that your source code has been successfully compiled.

The mvn test Command

The mvn test command is used to run the unit tests in your Maven project. When you execute this command, Maven compiles your code and then runs all test classes located in the src/test/java directory using the configured testing framework, such as JUnit.

This command triggers the test phase of the Maven build lifecycle. During this phase, Maven:

• Compiles the main source code;
• Compiles the test source code;
• Executes unit tests using the specified test framework.

If any tests fail, Maven will report them and stop the build process at this phase. Passing all tests is required before you can proceed to later phases, such as packaging or deployment.

Example: Running Tests from the Terminal

To run your project's unit tests, open a terminal in the root directory of your Maven project and enter:

mvn test

You will see output indicating the compilation and execution of tests, along with a summary of test results.

The mvn package Command

The mvn package command tells Maven to take your compiled Java code and bundle it into a distributable format, such as a JAR (Java ARchive) file. This makes your application easy to share, deploy, or use as a dependency in other projects.

When you run mvn package, Maven automatically executes several key phases of the build lifecycle:

• Validate: checks that the project is correct and all necessary information is available;
• Compile: compiles your source code;
• Test: runs unit tests using a framework like JUnit;
• Package: bundles the compiled code into a distributable format, such as a JAR file.

The most common use of mvn package is to prepare your application for deployment or distribution.

Example Terminal Command

mvn package

After running this command, look for a file like target/your-artifact-id-version.jar in your project directory. This file contains your packaged application, ready for use.