Master Maven: Essential Dependency Management and Plugin Configuration Guide

If you have development experience, you may have struggled with managing JAR files in the lib directory and dealing with compatibility issues; Maven dramatically simplifies this by handling project builds and dependencies.

Maven is a project management tool that can build Java projects and manage dependencies.

1. Repository Configuration

Maven introduces the concept of a repository. When you publish a JAR to a repository, other developers can reference it as a dependency; Maven first checks the central repository, then a private repository if configured, and finally the local repository.

2. Basic POM Information

groupId : usually the reversed domain of the organization.

artifactId : the project name.

version : the project version.

name : a short name for the project.

description : a brief description of the project.

Example POM snippet:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>xyz.ibudai</groupId>
  <artifactId>maven-demo</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <description>This is maven demo.</description>
</project>

3. Dependency Management

Define common dependencies in a dependencyManagement section so that sub‑modules can inherit version information without repeating it.

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.30</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13.2</version>
    </dependency>
  </dependencies>
</dependencyManagement>

Modules can then declare only the groupId and artifactId, inheriting the version from the parent.

4. Handling Transitive Dependencies

When a dependency itself depends on other libraries, Maven resolves the full dependency graph automatically. You only need to declare the direct dependency; Maven will pull in the required transitive ones.

5. Excluding and Optional Dependencies

Use the excludes tag to prevent specific transitive dependencies from being included, and the optional flag to stop a dependency from being transitively passed to downstream projects.

<dependency>
  <groupId>xyz.ibudai</groupId>
  <artifactId>demo-a</artifactId>
  <version>1.0.0</version>
  <excludes>
    <exclude>
      <groupId>xyz.ibudai</groupId>
      <artifactId>dependency-b</artifactId>
    </exclude>
  </excludes>
</dependency>

6. Variable Configuration

Define reusable version variables in a properties section and reference them with ${} placeholders.

<properties>
  <mysql.version>8.0.30</mysql.version>
  <junit.version>4.13.2</junit.version>
</properties>

<dependencies>
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>${mysql.version}</version>
  </dependency>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>${junit.version}</version>
  </dependency>
</dependencies>

7. Multi‑Module Projects

Use the modules tag in the parent POM to list sub‑modules. Sub‑modules inherit the parent’s configuration, including dependency management.

<modules>
  <module>module-1</module>
  <module>module-2</module>
</modules>

Example sub‑module POM (module‑1) inheriting the parent:

<parent>
  <groupId>xyz.ibudai</groupId>
  <artifactId>maven-demo</artifactId>
  <version>1.0-SNAPSHOT</version>
</parent>

<dependencies>
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
  </dependency>
</dependencies>

8. Plugin Management

8.1 Jar Plugin

The maven-jar-plugin lets you add custom entries to the JAR manifest, such as the main class.

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-jar-plugin</artifactId>
  <version>2.3.1</version>
  <configuration>
    <archive>
      <manifest>
        <mainClass>org.example.MyTest</mainClass>
        <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries>
        <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
      </manifest>
      <manifestEntries>
        <Plugin-Id>demo-plugin</Plugin-Id>
        <Plugin-Version>1.0.0</Plugin-Version>
      </manifestEntries>
    </archive>
  </configuration>
</plugin>

8.2 Assembly Plugin

The maven-assembly-plugin can create an "uber‑jar" that bundles all project dependencies.

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-assembly-plugin</artifactId>
  <version>3.1.0</version>
  <configuration>
    <descriptorRefs>
      <descriptorRef>jar-with-dependencies</descriptorRef>
    </descriptorRefs>
    <finalName>${project.artifactId}-${project.version}-all</finalName>
    <appendAssemblyId>false</appendAssemblyId>
    <attach>false</attach>
    <archive>
      <manifest>
        <mainClass>fully.qualified.MainClass</mainClass>
        <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries>
        <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
      </manifest>
    </archive>
  </configuration>
  <executions>
    <execution>
      <id>make-assembly</id>
      <phase>package</phase>
      <goals>
        <goal>single</goal>
      </goals>
    </execution>
  </executions>
</plugin>

8.3 Shade Plugin

The maven-shade-plugin also creates an uber‑jar but offers advanced features such as selective inclusion, class relocation, and filtering.

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-shade-plugin</artifactId>
  <version>3.2.0</version>
  <executions>
    <execution>
      <phase>package</phase>
      <goals>
        <goal>shade</goal>
      </goals>
    </execution>
  </executions>
  <configuration>
    <minimizeJar>true</minimizeJar>
    <artifactSet>
      <includes>
        <include>com.fasterxml.jackson.core:jackson-core</include>
      </includes>
    </artifactSet>
    <relocations>
      <relocation>
        <pattern>com.fasterxml.jackson.core</pattern>
        <shadedPattern>com.ibudai.fasterxml.jackson.core</shadedPattern>
      </relocation>
    </relocations>
    <filters>
      <filter>
        <artifact>*:*</artifact>
        <excludes>
          <exclude>META-INF/license/**</exclude>
          <exclude>META-INF/*</exclude>
          <exclude>LICENSE</exclude>
          <exclude>NOTICE</exclude>
        </excludes>
      </filter>
    </filters>
  </configuration>
</plugin>

9. Build‑time Settings

9.1 Compiler Plugin

Specify the Java source and target versions.

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-compiler-plugin</artifactId>
  <version>3.1</version>
  <configuration>
    <source>8</source>
    <target>8</target>
  </configuration>
</plugin>

9.2 Resource Exclusion

Exclude configuration files (e.g., application.yml) from the packaged JAR so they can be modified without rebuilding.

<resources>
  <resource>
    <directory>src/main/resources</directory>
    <excludes>
      <exclude>application.yml</exclude>
    </excludes>
  </resource>
</resources>

9.3 Main‑Class Configuration

Define the entry point of the application to avoid "no main class found" errors.

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>
    <mainClass>xyz.ibudai.TestWebApplication</mainClass>
    <layout>JAR</layout>
  </configuration>
</plugin>

By following these Maven configurations you can manage dependencies efficiently, build modular multi‑module projects, and create executable JARs with the exact content you need.