Introduction to Apache Maven

Maven is mainly used to build and manage Java projects, especially large-scale ones. It simplifies packaging, testing, and deploying Java applications. With Maven, developers can manage complex projects more easily using predefined lifecycles and project structures.

Key Terminologies:

1. POM Files: Project Object Model(POM) files are XML files that contain information related to the project and configuration information, such as dependencies, source directory, plugins, goals, etc., used by Maven to build the project. When you execute a Maven command, you give Maven a POM file to execute the commands. Maven reads the pom.xml file to accomplish its configuration and operations.
2. Dependencies and Repositories: Dependencies are external Java libraries required for a Project, and repositories are directories of packaged JAR files. The local repository is just a directory on your machine's hard drive. If the dependencies are not found in the local Maven repository, Maven downloads them from a central Maven repository and puts them in your local repository.
3. Build Life Cycles, Phases, and Goals: A build lifecycle consists of a sequence of build phases, and each build phase includes a sequence of goals. A Maven command typically refers to a build lifecycle, phase, or goal. If a lifecycle is executed using a Maven command, all build phases in that lifecycle are also executed. If a build phase is executed, all preceding phases in the defined sequence are also executed.
4. Build Profiles: Build profiles are a set of configuration values that allow you to build your project using different configurations. For example, you may want to build your project for local development, testing, or production. To enable these builds, you can define different build profiles in your pom.xml using its profiles element, which can be triggered in various ways.
5. Build Plugins: Build plugins are used to perform specific goals. You can add plugins to the pom.xml file. Maven offers standard plugins, and you can also implement custom plugins in Java.
   

Maven Architecture

Maven is built around two key components: POM (Project Object Model) and repositories.

1. Project Object Model (POM)

The pom.xml is the main component of any Maven project. It defines:

• Project metadata: groupId, artifactId, version
• Dependencies: External libraries needed
• Build setup: Plugins and lifecycle phases
• Project info: Developers, license, source control

2. Maven Repositories

Maven repositories are directories of packaged JAR files along with their metadata. The metadata are POM files related to the projects each packaged JAR file belongs to, including what external dependencies each packaged JAR has. Maven fetches and stores dependencies using three types of repositories:

1. Local repository: A local repository is a directory on the machine of developer. This repository contains all the dependencies Maven downloads. Maven only needs to download the dependencies once, even if multiple projects depends on them (e.g. ODBC). By default, maven local repository is user_home/m2 directory.

Example - C:\Users\asingh\.m2

2. Central repository: The central Maven repository is created Maven community. Maven looks in this central repository for any dependencies needed but not found in your local repository. Maven then downloads these dependencies into your local repository.

Example: Maven downloading the JUnit library from repo.maven.apache.org.

3. Remote repository: Remote repository is a repository on a web server from which Maven can download dependencies. It often used for hosting projects internal to the organization. Maven then downloads these dependencies into your local repository.

Example: A company’s internal Nexus server at http://nexus.company.com/repository/maven-releases.

Use Cases of Maven

Maven is a popular build automation and project management tool, especially for Java-based projects.

• Java Project Builds: Maven automates Java project builds, including tasks like compilation, testing, packaging (JAR, WAR), and deployment.
• Dependency Management: Maven simplifies dependency management by automatically downloading and including required libraries from central repositories, handling transitive dependencies.
• Continuous Integration and Delivery (CI/CD): Maven integrates with CI/CD tools like Jenkins, GitLab CI, and Travis CI, automating build, test, and deployment phases for rapid, consistent software delivery.
• Automated Testing: Maven works seamlessly with testing frameworks (e.g., JUnit, TestNG) to automate unit, integration, and other types of tests during the build process.
• Project Standardization and Documentation: Maven enforces a standardized project structure and generates comprehensive documentation, including dependency reports, test results, and code analysis.

Apache Maven is an essential tool for managing and automating Java project builds. It simplifies tasks like dependency management, project structuring, and reporting. With its standardized approach, Maven helps developers streamline their workflow and manage complex projects efficiently.

Introduction to Maven

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