What is the differences between dependencyManagement and dependencies in Maven

In Maven, the concepts of 'Dependency Management' and 'Dependencies' are related but serve distinct purposes and functionalities.

Dependency Management

Dependency Management is a feature of Maven, typically implemented using the <dependencyManagement> tag in the parent POM file. Through Dependency Management, we can centrally define the versions and scopes of dependencies for all modules at the project's top level. This ensures consistency across all submodules, preventing version conflicts.

For example, in a multi-module project, the dependency management configuration in the parent POM might look like:

xml
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>5.2.12.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.14.1</version>
        </dependency>
    </dependencies>
</dependencyManagement>

Dependencies

Dependencies refer to the external libraries required by the project during development. These dependencies are explicitly declared in the POM files of each module using the <dependencies> tag. These declarations inform Maven which external libraries to include during the build process, ensuring availability for compilation and runtime.

For example, a submodule might have the following dependency configuration:

xml
<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-core</artifactId>
    </dependency>
</dependencies>

Differences and Relationships

• Differences: Dependency Management is used to centrally manage dependency versions across multiple modules, whereas Dependencies specify the exact libraries required for a specific module.
• Relationships: When no version is specified for Dependencies, it defaults to the version defined in Dependency Management, ensuring consistency and maintainability of the project.

Through the above explanations and examples, we can see how Maven effectively controls and manages project dependencies through these two mechanisms, greatly simplifying project maintenance.