Master Maven: Essential Tips for Java Project Management and Dependency Handling

1. Basic Configuration

Maven introduces the concept of repositories; when a dependency is declared, Maven first checks the local repository, then the central repository, and optionally a private repository before downloading the JAR to the local cache.

A minimal Maven project pom.xml should contain the three essential elements: groupId, artifactId, and version.

<?xml version="1.0" encoding="UTF-8"?>
<project ...>
    <!-- Fixed 4.0.0, specifies the POM model version -->
    <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>

2. Dependency Management

1. Dependency Introduction

Dependencies are added with the dependencies tag.

<dependencies>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.27</version>
        <scope>runtime</scope>
    </dependency>
</dependencies>

2. Transitive Dependencies

Maven automatically resolves transitive dependencies; you only need to declare the direct dependency, and Maven pulls in its required libraries.

3. Dependency Exclusion

When a transitive dependency causes conflicts, it can be excluded using the excludes element.

<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>

4. Variable Configuration

Version numbers and other repeated values can be centralized with properties and referenced via ${}.

<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>

3. Module Configuration

1. Module Management

Multi‑module projects list sub‑modules with the modules tag.

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

2. Module Inheritance

Sub‑modules inherit configuration from a parent pom via the parent element. If groupId or version are omitted, they are taken from the parent.

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

<artifactId>module-1</artifactId>

4. Unified Management

1. Dependency Management

Common dependencies are declared once in the parent pom’s dependencyManagement section; child modules only need to list the artifact without version.

<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>

5. Plugin Management

1. Jar Plugin

The maven-jar-plugin can add custom entries to the JAR manifest.

<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>

2. Assembly Plugin

The maven-assembly-plugin creates a 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>
    </configuration>
    <executions>
        <execution>
            <id>make-assembly</id>
            <phase>package</phase>
            <goals>
                <goal>single</goal>
            </goals>
        </execution>
    </executions>
</plugin>

3. Shade Plugin

The maven-shade-plugin produces an uber JAR, can relocate packages, and filter unwanted files.

<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>

6. Build Configuration

1. JDK Version

Set the Java source and target versions with the maven-compiler-plugin.

<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>

2. Resource Exclusion

Exclude configuration files (e.g., application.yml) from the packaged JAR.

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

3. Main Class

Define the entry point class for executable JARs, for example with the Spring Boot plugin.

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