Handling Dependency Conflicts

One of Maven’s biggest strengths is its ability to manage transitive dependencies — libraries your dependencies need.
But this convenience can sometimes lead to dependency conflicts, especially when different libraries pull in different versions of the same artifact.

If not handled correctly, this can cause:

• ClassNotFoundException or NoSuchMethodError at runtime
• Unexpected behavior due to version mismatches
• Larger build sizes with redundant JARs

In this lesson, you’ll learn how to handle dependency conflicts using:

• The <dependencyManagement> section
• Explicit version overriding
• The mvn dependency:analyze command

1. Using <dependencyManagement>

The <dependencyManagement> section in pom.xml allows you to control dependency versions centrally.
This is especially useful in multi-module Maven projects, where multiple child modules depend on the same libraries.

Example: Centralized Dependency Management

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>2.0.9</version>
        </dependency>
    </dependencies>
</dependencyManagement>

• Child modules only need to declare the dependency without specifying a version:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
</dependency>

Maven will automatically use the version defined in <dependencyManagement>.

✅ Benefit: This ensures consistent versions across all modules and avoids version mismatches.

2. Overriding Versions

If two libraries bring in different versions of the same dependency, Maven will choose one (usually the nearest one in the dependency tree).

To explicitly control which version Maven should use, you can override the version in your pom.xml.

Example: Overriding a Transitive Dependency Version

<dependencies>
    <!-- Your direct dependency -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <version>3.1.0</version>
    </dependency>

    <!-- Override conflicting dependency -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.15.2</version>
    </dependency>
</dependencies>

This ensures Maven uses your declared version instead of the transitive one.

3. Running mvn dependency:analyze

Maven provides a helpful command to analyze dependencies:

mvn dependency:analyze

✅ What It Does:

• Lists declared but unused dependencies
• Lists used but undeclared dependencies
• Helps identify conflicts and unnecessary libraries

Example Output

[WARNING] Used undeclared dependencies:
   com.google.guava:guava:jar:31.1-jre:compile
[WARNING] Unused declared dependencies:
   commons-logging:commons-logging:jar:1.2:compile

✅ Benefit: This helps you clean up your pom.xml and reduce build size, while also spotting hidden dependency issues.

Best Practices to Avoid Conflicts

• Always define critical dependencies explicitly in your pom.xml.
• Use <dependencyManagement> in multi-module projects for version consistency.
• Regularly run:

mvn dependency:tree
mvn dependency:analyze

• Keep dependencies updated to stable versions.

Key Takeaways

• <dependencyManagement> ensures consistent dependency versions across projects.
• Overriding versions lets you take control when conflicts arise.
• mvn dependency:analyze helps detect unused or missing dependencies, making builds leaner and safer.