Build Tools: Maven and Gradle

Build tools automate compilation, testing, packaging, and dependency management. Maven and Gradle are the two dominant build tools in the Java ecosystem.

Maven vs Gradle

Feature	Maven	Gradle
Config Format	XML (pom.xml)	Groovy/Kotlin (build.gradle)
Build Speed	Slower	Faster (incremental builds)
Learning Curve	Easier (convention)	Steeper (more flexible)
Flexibility	Convention over config	Highly customizable
IDE Support	Excellent	Excellent

Maven

Maven uses pom.xml (Project Object Model) for configuration.

Project Structure

my-project/
├── pom.xml
├── src/
│   ├── main/
│   │   ├── java/          # Application source code
│   │   └── resources/     # Config files, properties
│   └── test/
│       ├── java/          # Test source code
│       └── resources/     # Test resources
└── target/                # Compiled output (generated)

Basic pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <!-- Project coordinates -->
    <groupId>com.example</groupId>
    <artifactId>my-app</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <!-- JUnit 5 for testing -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>5.10.0</version>
            <scope>test</scope>
        </dependency>

        <!-- SLF4J for logging -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>2.0.9</version>
        </dependency>
    </dependencies>
</project>

Common Maven Commands

Command	Description
mvn clean	Delete target directory
mvn compile	Compile source code
mvn test	Run unit tests
mvn package	Create JAR/WAR file
mvn install	Install to local repository
mvn clean install	Clean, compile, test, and install
mvn dependency:tree	Show dependency hierarchy

Dependency Scopes

<!-- compile (default): Available everywhere -->
<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>32.1.2-jre</version>
</dependency>

<!-- provided: Available at compile, not packaged (e.g., servlet API) -->
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
    <scope>provided</scope>
</dependency>

<!-- test: Only for testing -->
<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter</artifactId>
    <version>5.10.0</version>
    <scope>test</scope>
</dependency>

<!-- runtime: Not needed for compilation, only at runtime -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.33</version>
    <scope>runtime</scope>
</dependency>

Gradle

Gradle uses Groovy or Kotlin DSL for configuration.

Basic build.gradle

plugins {
    id 'java'
    id 'application'
}

group = 'com.example'
version = '1.0.0'

java {
    sourceCompatibility = JavaVersion.VERSION_17
    targetCompatibility = JavaVersion.VERSION_17
}

repositories {
    mavenCentral()
}

dependencies {
    // Implementation dependencies
    implementation 'com.google.guava:guava:32.1.2-jre'
    implementation 'org.slf4j:slf4j-api:2.0.9'

    // Test dependencies
    testImplementation 'org.junit.jupiter:junit-jupiter:5.10.0'
    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
}

application {
    mainClass = 'com.example.Main'
}

test {
    useJUnitPlatform()
}

Common Gradle Commands

Command	Description
./gradlew build	Compile, test, and package
./gradlew clean	Delete build directory
./gradlew test	Run unit tests
./gradlew run	Run the application
./gradlew dependencies	Show dependency tree
./gradlew tasks	List available tasks

Creating Executable JARs

Maven (with shade plugin)

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>3.5.0</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals><goal>shade</goal></goals>
                    <configuration>
                        <transformers>
                            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <mainClass>com.example.Main</mainClass>
                            </transformer>
                        </transformers>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Gradle (fat JAR)

jar {
    manifest {
        attributes 'Main-Class': 'com.example.Main'
    }
    // Include all dependencies in the JAR
    from {
        configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) }
    }
    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
}

Multi-Module Projects

Maven Parent POM

<!-- parent/pom.xml -->
<project>
    <groupId>com.example</groupId>
    <artifactId>parent</artifactId>
    <version>1.0.0</version>
    <packaging>pom</packaging>

    <modules>
        <module>core</module>
        <module>web</module>
        <module>api</module>
    </modules>

    <dependencyManagement>
        <dependencies>
            <!-- Version managed here, used in children -->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>3.1.5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

Summary