List conflicting dependencies in the Maven reactor

The Maven Dependency Plugin among other things include a dependency:analyze-duplicate

The dependency plugin provides the capability to manipulate artifacts. It can copy and/or unpack artifacts from local or remote repositories to a specified location.

This Apache #Maven plugin is really feature rich and provide a lot of interesting goals:

• dependency:analyze analyzes the dependencies of this project and determines which are: used and declared; used and undeclared; unused and declared.
• dependency:analyze-dep-mgt analyzes your projects dependencies and lists mismatches between resolved dependencies and those listed in your dependencyManagement section.
• dependency:analyze-only is the same as analyze, but is meant to be bound in a pom. It does not fork the build and execute test-compile.
• dependency:analyze-report analyzes the dependencies of this project and produces a report that summarises which are: used and declared; used and undeclared; unused and declared.
• dependency:analyze-duplicate analyzes the dependencies/ and dependencyManagement/ tags in the pom.xml and determines the duplicate declared dependencies.
• dependency:build-classpath tells Maven to output the path of the dependencies from the local repository in a classpath format to be used in java -cp. The classpath file may also be attached and installed/deployed along with the main artifact.
• dependency:copy takes a list of artifacts defined in the plugin configuration section and copies them to a specified location, renaming them or stripping the version if desired. This goal can resolve the artifacts from remote repositories if they don’t exist in local.
• dependency:copy-dependencies takes the list of project direct dependencies and optionally transitive dependencies and copies them to a specified location, stripping the version if desired. This goal can also be run from the command line.
• dependency:get downloads a single artifact transitively from a specified remote repository.
• dependency:go-offline tells Maven to resolve everything this project is dependent on (dependencies, plugins, reports) in preparation for going offline.
• dependency:list alias for resolve that lists the dependencies for this project.
• dependency:properties set a property for each project dependency containing the to the artifact on the file system.
• dependency:purge-local-repository tells Maven to clear all dependency-artifact files out of the local repository, and optionally re-resolve them.
• dependency:resolve tells Maven to resolve all dependencies and displays the version.
• dependency:resolve-plugins Tells Maven to resolve plugins and their dependencies.
• dependency:sources tells Maven to resolve all dependencies and their source attachments, and displays the version.
• dependency:tree displays the dependency tree for this project.
• dependency:unpack removes the project dependencies from the local repository, and optionally re-resolve them.
• dependency:unpack-dependencies like copy-dependencies but unpacks

It can be use to make the build failing (There is another way to do this using the enforcer plugin as well)

To detect duplicate dependencies just run against your pom

mvn org.apache.maven.plugins:maven-dependency-plugin:2.2:analyze-duplicate

When you have found the duplicate you can query and analyze why it was included by running

mvn dependency:tree -Dverbose -Dincludes=:xerces*::

or use M2Eclipse dependencies graph or dependency tree that support highlighting and query with wildcards as well. I like especially this solution because I can right click on any dependencies and select “add exclusions” and let M2Eclipse modify the pom.xml for me.