Dependencies Management

What are Dependencies?

Dependencies are external libraries (JAR files) that your project needs to compile and run.

Adding Dependencies

<dependencies>
    <!-- Basic dependency -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <version>3.2.0</version>
    </dependency>

    <!-- Test dependency -->
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter</artifactId>
        <version>5.10.0</version>
        <scope>test</scope>
    </dependency>

    <!-- Optional dependency -->
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.30</version>
        <optional>true</optional>
    </dependency>
</dependencies>

Dependency Scopes

<!-- Examples -->
<dependency>
    <groupId>jakarta.servlet</groupId>
    <artifactId>jakarta.servlet-api</artifactId>
    <version>6.0.0</version>
    <scope>provided</scope>  <!-- Tomcat provides this -->
</dependency>

<dependency>
    <groupId>org.postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <version>42.6.0</version>
    <scope>runtime</scope>  <!-- Not needed at compile time -->
</dependency>

Dependency Management

<!-- Parent POM - define versions centrally -->
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-framework-bom</artifactId>
            <version>6.1.0</version>
            <type>pom</type>
            <scope>import</scope>  <!-- Import BOM -->
        </dependency>
    </dependencies>
</dependencyManagement>

<!-- Child POM - no version needed! -->
<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <!-- Version from BOM -->
    </dependency>
</dependencies>

Excluding Transitive Dependencies

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <!-- Exclude Tomcat to use Jetty instead -->
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<!-- Add Jetty instead -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

Useful Commands

# Show dependency tree
mvn dependency:tree

# Show tree for specific artifact
mvn dependency:tree -Dincludes=org.springframework

# Find unused dependencies
mvn dependency:analyze

# Download sources and javadocs
mvn dependency:sources
mvn dependency:resolve -Dclassifier=javadoc

# Check for updates
mvn versions:display-dependency-updates

Finding Dependencies

Summary