Managing Classpath Clashes in Gradle: Tips and Tools

When you’re working on a java project, one of the most common issues you might encounter is classpath clashes. Classpath clashes occur when multiple libraries bring in different versions of the same class or when two different classes have the same fully-qualified name. These clashes can lead to runtime errors, unexpected behavior, or even crashes.

In this article, we’ll discuss some tips and tools for detecting and preventing classpath clashes in your Gradle projects, as well as some third-party plugins that can help simplify the process.

Built-in Gradle tools

To detect classpath clashes in your Gradle project, you can use several built-in tools provided by Gradle, such as the dependencyInsight task and the gradle dependencies command. These tools allow you to inspect the dependency tree for your project and identify any potential conflicts between different library versions.
You can also use the failOnVersionConflict() method, which is available in the Gradle Dependency Management plugin, to fail the building or tests in case of classpath collisions. This method can be added to the dependencyManagement block or the test task in your build.gradle file. However, Gradle’s built-in dependency management features won’t detect classpath clashes that involve the same class name in different libraries.
In that case, you may need to use a third-party plugins.

Third-party plugins

There are third-party plugins available for Gradle that can help detect and resolve classpath clashes. Two popular plugins for this purpose are gradle-duplicate-classes-check and classpathHell.

gradle-duplicate-classes-check

The gradle-duplicate-classes-check plugin scans your project’s dependencies and identifies any classes that have the same fully-qualified name, even if they come from different libraries. It can generate a report that shows the location of each duplicate class and which libraries contain it. This can help you identify any conflicts and take steps to resolve them.
Here’s an example build.gradle file that demonstrates how to use the gradle-duplicate-classes-check plugin:

plugins {
    id 'java'
    id 'com.github.tehlers.duplicate-classes-check' version '0.2.2'
}

dependencies {
    // your project dependencies here
}

With this configuration, you can run the duplicateClassesCheck task to check for duplicate classes in your project’s dependencies.

classpathHell

The classpathHell plugin provides a similar functionality, but with additional features like support for multiple configurations, exclusion patterns, and custom messages. It also provides a task that can be used to generate a report of all classpath conflicts detected in your project.
Here’s an example build.gradle file that demonstrates how to use the classpathHell plugin:

plugins {
    id 'java'
    id 'de.set.gradle.classpath-hell' version '1.1.4'
}

classpathHell {
    // your configuration here
}

dependencies {
    // your project dependencies here
}

Once you’ve identified any duplicate classes or classpath clashes in your project, you can take steps to resolve the conflicts. This might involve excluding one of the libraries that contains the duplicate class, using a different version of one of the libraries that doesn’t have the duplicate class, or restructuring your dependencies to avoid conflicts altogether.

In conclusion

While Gradle’s built-in features can help manage dependencies in your projects, they may not detect all types of classpath clashes. It’s important to pay attention to any potential conflicts and to use third-party plugins or other tools as needed to detect and resolve these issues. With the help of tools like gradle-duplicate-classes-check and classpathHell, you can ensure that your Gradle projects are free of classpath clashes and run smoothly.