Shaping Your Dependencies: Using Maven Shade Plugin for Selective Inclusion of "provided" Scope Classes
Maven's "provided" scope is designed for dependencies that are assumed to be available at runtime but aren't required for compilation. This often applies to server-side libraries that the application container or environment provides. However, sometimes you might need to include specific classes from a "provided" dependency within your final artifact for various reasons, such as:
- Dependency Conflicts: The "provided" dependency might conflict with another dependency in your project, requiring you to selectively include specific classes to resolve the conflict.
- Custom Logic: You might need to extend or override certain classes from the "provided" dependency for custom functionality.
- Integration: Your application might need to rely on classes from the "provided" dependency for internal integration or to provide specific functionality to other parts of the application.
The Maven Shade Plugin offers a powerful solution for achieving this selective inclusion. Let's dive into how to leverage it effectively.
The Scenario and Original Code
Let's assume you have a project that uses a "provided" dependency, provided-lib, and you need to include the MySpecificClass from this dependency in your final artifact. Here's a sample pom.xml snippet demonstrating this situation:
<dependency>
<groupId>com.example</groupId>
<artifactId>provided-lib</artifactId>
<version>1.0.0</version>
<scope>provided</scope>
</dependency>
Now, by default, provided-lib won't be included in the final artifact due to its "provided" scope. To selectively include MySpecificClass, we'll need to configure the Maven Shade Plugin.
Maven Shade Plugin to the Rescue
The Maven Shade Plugin is your go-to tool for manipulating your project's dependencies during the packaging process. Here's how you can configure it to include only MySpecificClass:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.3.0</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<relocations>
<relocation>
<pattern>com.example.provided-lib.MySpecificClass</pattern>
<shadedPattern>com.example.myproject.shaded.MySpecificClass</shadedPattern>
</relocation>
</relocations>
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<mainClass>com.example.myproject.App</mainClass>
</transformer>
</transformers>
</configuration>
</execution>
</executions>
</plugin>
Explanation:
- relocations: This element allows you to rename and relocate specific classes within your final artifact. The
patterndefines the class you want to relocate, while theshadedPatterndefines the new location and name. - transformers: This element allows you to modify the artifact's manifest file. Here, we set the main class for the application.
In this configuration, MySpecificClass from provided-lib is relocated to com.example.myproject.shaded.MySpecificClass. This ensures that it is included in the final artifact, while other classes from provided-lib remain excluded.
Additional Insights and Considerations
- Dependencies: Remember to check the transitive dependencies of your "provided" dependency to ensure you don't accidentally include unwanted classes.
- Conflicts: The Maven Shade Plugin can help resolve dependency conflicts by allowing you to relocate classes.
- Alternative Solutions: In some cases, using a different scope for the dependency (e.g., "compile") might be a better approach. This depends on the specific needs of your project.
- Testing: Always test your application thoroughly after using the Maven Shade Plugin to ensure the changes haven't introduced any unexpected behavior.
By applying the techniques described above, you can gain granular control over your dependency inclusion process. This enables you to tailor your project's packaging and deployment strategy to meet specific requirements.
References and Resources
- Maven Shade Plugin documentation: Detailed information about the Maven Shade Plugin and its various configurations.
- Maven Dependency Scopes: A comprehensive guide to Maven's dependency scopes.
- Maven Plugins: Explore the vast collection of Maven plugins available for enhancing your build process.
By understanding these concepts and employing the Maven Shade Plugin effectively, you can build robust and adaptable applications while navigating the complexities of dependency management.
