DepClean

What is DepClean?

DepClean is a Maven plugin that automatically detects and removes unused dependencies declared in a project's pom.xml file, imported transitively through other dependencies, and even those inherited from a parent POM.

It can be executed via the command line as a Maven goal or seamlessly integrated into the Maven build lifecycle (e.g., in CI/CD pipelines).

Importantly, DepClean does not modify your source code or original pom.xml file.

Main Features

• Automatically detects and removes unused dependencies from the pom.xml, including those inherited from parent projects.
• Fully supports Java 21 bytecode analysis, ensuring compatibility with modern Java features.
• Generates a clean and minimal pom.xml, free from unused dependencies.
• Produces detailed, per-dependency usage reports.
• Offers fine-grained configuration options to tailor the analysis and cleaning process.
• Integrates directly into the Maven build lifecycle.
• Handles multi-module Maven projects out of the box.
• Ignores some dependencies used only via reflection (e.g., frameworks like Spring or Hibernate).
• Includes support for annotation processors.
• Analyzes fat JARs, shaded dependencies, and repackaged libraries.

For a visual overview of how DepClean works and what it can do for your project, check out the companion project: depclean-web.

✨ DepClean is the result of academic research conducted at KTH Royal Institute of Technology in Sweden. It was introduced in the paper: "A Comprehensive Study of Bloated Dependencies in the Maven Ecosystem" (DOI: 10.1007/s10664-020-09914-8)

Usage

Configure the pom.xml file of your Maven project to use DepClean as part of the build:

xml <plugin> <groupId>se.kth.castor</groupId> <artifactId>depclean-maven-plugin</artifactId> <version>2.2.0-SNAPSHOT</version> <executions> <execution> <goals> <goal>depclean</goal> </goals> </execution> </executions> </plugin>

Or you can run DepClean directly from the command line.

bash cd {PATH_TO_MAVEN_PROJECT} mvn compile mvn compiler:testCompile mvn se.kth.castor:depclean-maven-plugin:2.2.0-SNAPSHOT:depclean

Let's see an example of running DepClean version 2.0.1 in the project Apache Commons Numbers!

Optional Parameters

The Maven plugin can be configured with the following additional parameters.

| Name | Type | Description | | :------------------------- | :-----------: | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | <ignoreDependencies> | Set<String> | A regex expression matching dependencies to be ignored by DepClean during the analysis (i.e., considered as used). This is useful to bypass incomplete result caused by bytecode-level analysis. For example: -DignoreDependencies="net.bytebuddy:byte-buddy:.*","com.google.guava.*" ignores dependencies with groupId:artifactId equals to net.bytebuddy:byte-buddy and groupId equals to com.google.guava. | | <ignoreScopes> | Set<String> | Add a list of scopes, to be ignored by DepClean during the analysis. Useful to not analyze dependencies with scopes that are not needed at runtime. Valid scopes are: compile, provided, test, runtime, system, import. An Empty string indicates no scopes (default). | | <ignoreTests> | boolean | If this is true, DepClean will not analyze the test classes in the project, and, therefore, the dependencies that are only used for testing will be considered unused. This parameter is useful to detect dependencies that have compile scope but are only used for testing. Default value is: false. | | <createPomDebloated> | boolean | If this is true, DepClean creates a debloated version of the pom without unused dependencies called debloated-pom.xml, in the root of the project. Default value is: false. | | <createResultJson> | boolean | If this is true, DepClean creates a JSON file of the dependency tree along with metadata of each dependency. The file is called depclean-results.json, and is located in the target directory of the project. Default value is: false. | | <createCallGraphCsv> | boolean | If this is true, DepClean creates a CSV file with the static call graph of the API members used in the project. The file is called depclean-callgraph.csv, and is located in the target directory of the project. Default value is: false. | | <failIfUnusedDirect> | boolean | If this is true, and DepClean reported any unused direct dependency in the dependency tree, the build fails immediately after running DepClean. Default value is: false. | | <failIfUnusedTransitive> | boolean | If this is true, and DepClean reported any unused transitive dependency in the dependency tree, the build fails immediately after running DepClean. Default value is: false. | | <failIfUnusedInherited> | boolean | If this is true, and DepClean reported any unused inherited dependency in the dependency tree, the build fails immediately after running DepClean. Default value is: false. | | <skipDepClean> | boolean | Skip plugin execution completely. Default value is: false. |

You can integrate DepClean in your CI/CD pipeline. For example, if you want to fail the build in the presence of unused direct dependencies, while ignoring all the dependency scopes except the compile, use the following plugin configuration.

xml <plugin> <groupId>se.kth.castor</groupId> <artifactId>depclean-maven-plugin</artifactId> <version>2.2.0-SNAPSHOT</version> <executions> <execution> <goals> <goal>depclean</goal> </goals> <configuration> <failIfUnusedDirect>true</failIfUnusedDirect> <ignoreScopes>provided,test,runtime,system,import</ignoreScopes> </configuration> </execution> </executions> </plugin>

Of course, it is also possible to execute DepClean with parameters directly from the command line. The previous example can be executed directly as follows:

bash mvn se.kth.castor:depclean-maven-plugin:2.2.0-SNAPSHOT:depclean -DfailIfUnusedDirect=true -DignoreScopes=provided,test,runtime,system,import

How does DepClean works?

DepClean runs before executing the package phase of the Maven build lifecycle. It statically collects all the types referenced in the project under analysis as well as in its declared dependencies. Then, it compares the types that the project actually use in the bytecode with respect to the class members belonging to its dependencies.

With this usage information, DepClean constructs a new pom.xml based on the following steps:

1. add all used transitive dependencies as direct dependencies
2. remove all unused direct dependencies
3. exclude all unused transitive dependencies

If all the tests pass, and the project builds correctly after these changes, then it means that the dependencies identified as bloated can be removed. DepClean produces a file named pom-debloated.xml, located in the root of the project, which is a clean version of the original pom.xml without bloated dependencies.

Installing and building from source

Prerequisites:

• Java OpenJDK 17 or above
• Apache Maven

In a terminal clone the repository and switch to the cloned folder:

bash git clone https://github.com/castor-software/depclean.git cd depclean

Then run the following Maven command to build the application and install the plugin locally:

bash mvn clean install

License

Distributed under the MIT License. See LICENSE for more information.

Funding

DepClean is partially funded by the Wallenberg Autonomous Systems and Software Program (WASP).