How to Slim Down Maven Builds Using Optional and Scope Settings

Overview

Improper Maven dependency configuration—especially the optional flag and scope element—can cause oversized JAR/WAR files, slower compilation, and unnecessary transitive conflicts. Correct usage reduces artifact size and improves build performance.

optional Element

The optional flag marks a dependency as non‑transitive. When set to true the dependency is not passed to downstream projects.

<!-- spring‑boot‑devtools as an optional dependency -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <optional>true</optional>
</dependency>

If a parent project (A) declares a dependency without optional, the child project (B) inherits it and the JAR is packaged into B’s artifact. The default value of optional is false.

When optional is set to true in the parent, the child can decide whether to include the dependency. The child may either keep the parent’s optional flag or declare the dependency explicitly.

Even if the dependency is defined inside a <dependencyManagement> section with optional set to true, child modules can still add the dependency explicitly, overriding the optional setting.

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <optional>true</optional>
        </dependency>
    </dependencies>
</dependencyManagement>

scope Element

The scope element controls where a dependency is available and whether it is transitive. Common values are compile, provided, runtime, test, and system.

compile (default) – Available for compilation, testing, and runtime; packaged into the final artifact.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

test – Used only for test compilation and execution; omitted from the packaged artifact.

<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>

runtime – Not needed for compilation but required at runtime (e.g., JDBC driver).

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.20</version>
    <scope>runtime</scope>
</dependency>

provided – Available for compilation and testing but not packaged because the runtime environment supplies it (e.g., servlet API).

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <scope>provided</scope>
</dependency>

system – Similar to provided but the artifact is retrieved from a local file system path via systemPath. Its use is discouraged.

<dependency>
    <groupId>sun.jdk</groupId>
    <artifactId>tools</artifactId>
    <version>1.5.0</version>
    <scope>system</scope>
    <systemPath>${java.home}/../lib/tools.jar</systemPath>
</dependency>

Transitivity depends on the scope used by an intermediate project. If project B depends on A with test or provided, a downstream project C will not inherit A’s dependencies. With compile or runtime, the transitive relationship is preserved.

Applying optional and appropriate scope values enables developers to keep Maven artifacts lean, accelerate compilation and deployment, and avoid unnecessary dependency conflicts.