Dependency Convergence

This rule requires that dependency version numbers converge. If a project has two dependencies, A and B, both depending on the same artifact, C, this rule will fail the build if A depends on a different version of C then the version of C depended on by B.

Here is a concrete example.

This will cause a build to fail.

  <dependencies>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-jdk14</artifactId>
      <version>1.6.1</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-nop</artifactId>
      <version>1.6.0</version>
    </dependency>
  </dependencies>  

With this being logged during compilation

Dependency convergence error for org.slf4j:slf4j-api1.6.1 paths to dependency are:

[ERROR]
Dependency convergence error for org.slf4j:slf4j-api:1.6.1 paths to dependency are:
+-org.myorg:my-project:1.0.0-SNAPSHOT
  +-org.slf4j:slf4j-jdk14:1.6.1
    +-org.slf4j:slf4j-api:1.6.1
and
+-org.myorg:my-project:1.0.0-SNAPSHOT
  +-org.slf4j:slf4j-nop:1.6.0
    +-org.slf4j:slf4j-api:1.6.0

And this will succeed.

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-jdk14</artifactId>
      <version>1.6.1</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-nop</artifactId>
      <version>1.6.0</version>
      <exclusions>
        <exclusion>
          <groupId>org.slf4j</groupId>
          <artifactId>slf4j-api</artifactId>
        </exclusion>
      </exclusions>
    </dependency>

Here is how a project should be setup to use this rule

<project>
  ...
  <build>
    <plugins>
      ...
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-enforcer-plugin</artifactId>
        <version>1.3.1</version>
        <executions>
          <execution>
            <id>enforce</id>
            <configuration>
              <rules>
                <DependencyConvergence/>
              </rules>
            </configuration>
            <goals>
              <goal>enforce</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      ...
    </plugins>
  </build>
  ...
</project>

Timestamped version

By default the non-unique versions are matched, which means the X.Y-SNAPSHOT instead of the timestamped versions. If you want to use the unique versions of the dependencies, you can set its property to true.

      <DependencyConvergence>
        <uniqueVersions>true</uniqueVersions> 
      </DependencyConvergence>