Understanding of Mavne Structure

Introduction to Maven

• Maven is a build automation and project management tool for Java & Spring Boot applications.
• It uses POM (Project Object Model) to define project configuration.
• Maven → defines what to do.
• Ant → defines what to do and how to do.
• When you run a Maven command, it looks for pom.xml in the current directory.

What Maven Provides

• Build generation → Compile, test, package Spring Boot JAR/WAR.
• Dependency resolution → Downloads Spring Boot starter dependencies.
• Documentation → Generates Javadocs, project reports.

Maven Project Structure

my-springboot-app/
 ├── pom.xml                 (Project Object Model)
 └── src
     ├── main
     │   ├── java            (Spring Boot source code)
     │   │    └── com/example/DemoApplication.java
     │   └── resources       (application.properties, static/, templates/)
     └── test
         ├── java            (Unit & Integration tests)
         └── resources

• src/main/java → Application code (Spring Boot controllers, services, repos).
• src/main/resources → Config (application.yml, logback.xml, static files).
• src/test/java → Unit tests using JUnit/Mockito.

POM Types

• Parent POM: Common configs for multi-module Spring Boot projects.
• Super POM: Default Maven POM (all projects inherit from it implicitly).
• Repositories:
  • Local repo → ~/.m2/repository
  • Remote repo → Central, Nexus, Artifactory
• Dependencies: Libraries required by the app.

<!-- Example Spring Boot Parent POM -->
<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>3.1.0</version>
  <relativePath/> <!-- lookup parent from repository -->
</parent>

<dependencies>
  <!-- Spring Boot Starter Web -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>

  <!-- Testing -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
  </dependency>
</dependencies>

Maven Build Lifecycle (Phases with Spring Boot Examples)

• Maven lifecycle = sequence of phases.
• Running a phase executes all previous phases.
• Each phase has goals (tasks) controlled by plugins.

• Ensures project structure is valid.
• In Spring Boot → can run Checkstyle/Spotless plugin for code style validation.

# Validate project
mvn validate

<plugin>
  <groupId>com.diffplug.spotless</groupId>
  <artifactId>spotless-maven-plugin</artifactId>
  <version>2.38.0</version>
  <executions>
    <execution>
      <phase>validate</phase>
      <goals>
        <goal>check</goal>
      </goals>
    </execution>
  </executions>
</plugin>

• Compiles Spring Boot application source code (src/main/java).
• Output → target/classes.

# Compile sources
mvn compile

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-compiler-plugin</artifactId>
  <version>3.11.0</version>
  <configuration>
    <source>17</source>
    <target>17</target>
  </configuration>
</plugin>

• Runs JUnit/Mockito/Spring Boot tests in src/test/java.
• Uses Surefire Plugin.

# Run unit tests
mvn test

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-surefire-plugin</artifactId>
  <version>3.1.2</version>
</plugin>

• Creates a JAR/WAR of the Spring Boot app.
• Spring Boot uses spring-boot-maven-plugin for executable JARs.

# Create executable jar
mvn package

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
</plugin>

• Runs integration tests, code quality checks (PMD/SpotBugs).

# Run static analysis
mvn verify

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-pmd-plugin</artifactId>
  <version>3.21.2</version>
  <executions>
    <execution>
      <phase>verify</phase>
      <goals>
        <goal>check</goal>
      </goals>
    </execution>
  </executions>
</plugin>

• Installs Spring Boot JAR into local repo (~/.m2/repository).
• Other local projects can depend on it.

# Install in local repo
mvn install

<dependency>
  <groupId>com.example</groupId>
  <artifactId>my-springboot-app</artifactId>
  <version>1.0-SNAPSHOT</version>
</dependency>

• Deploys Spring Boot artifact to remote repo (Nexus, Artifactory).
• Used for CI/CD pipelines in enterprises.

# Deploy to remote repo
mvn deploy

<distributionManagement>
  <repository>
    <id>company-releases</id>
    <url>https://nexus.company.com/repository/maven-releases/</url>
  </repository>
  <snapshotRepository>
    <id>company-snapshots</id>
    <url>https://nexus.company.com/repository/maven-snapshots/</url>
  </snapshotRepository>
</distributionManagement>

Key Points to Remember

• Run mvn test → validate → compile → test (all previous phases included).
• Goal = task (e.g., compiler:compile, spring-boot:run).
• settings.xml → Used to define:
  • Local repo path
  • Remote server credentials
  • Proxies