How to use of the Maven Enforcer plugin?

Question

I'd like to use the Maven Enforcer plugin to check to see if I have duplicate classes on my path.

I've tried the example from here.

But when I run it like this:

mvn enforcer:enforce

I get this error:

Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:1.0.1:enforce (default-cli) on project datapopulator: The parameters 'rules' for goal org.apache.maven.plugins:maven-enforcer-plugin:1.0.1:enforce are missing or invalid

Is there a way to use this correctly?

EDIT #1

If changing my config to this:

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-enforcer-plugin</artifactId>
            <version>1.0.1</version>
            <executions>
                <execution>
                    <id>enforce-versions</id>
                    <goals>
                        <goal>enforce</goal>
                    </goals>
                    <configuration>
                        <rules>
                            <AlwaysPass />
                        </rules>
                        <fail>true</fail>
                    </configuration>
                </execution>
            </executions>
        </plugin>

Produces the same error.

Answer 1

The reason why your first version did not work is because there is a difference between a plug-in configuration inside the execution tag and a plug-in configuration outside the execution tag. The execution is only used when your plug-in is triggered by a special phase of the complete Maven build.

The Maven guide to configuration explains it better:

Configurations inside the tag differ from those that are outside in that they cannot be used from a direct command line invocation. Instead they are only applied when the lifecycle phase they are bound to are invoked. Alternatively, if you move a configuration section outside of the executions section, it will apply globally to all invocations of the plugin.

Answer 2

Try this, moving the configuration outside executions, so it isn't bound to the life cycle phase.

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-enforcer-plugin</artifactId>
    <version>1.0.1</version>
    <executions>
        <execution>
            <id>enforce-versions</id>
            <goals>
                <goal>enforce</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <rules>
            <AlwaysPass />
        </rules>
        <fail>true</fail>
    </configuration>
</plugin>

Now when you do mvn enforcer:enforce, it picks the rules from your pom.xml.

Answer 3

See these answers

You can use the special default command line execution id, default-cli to invoke it (see Maven Docs), see my example below. This works at least with 3.1.1 and the article cited says it should work with 2.2.0+

mvn enforcer:enforce

However if you are using above Maven 3.1.1 (I can confirm it works in 3.3.3 with enforcer v 1.4.1) you can specify the execution id you wish using the new @ syntax (see Maven JIRA and the answers above);

e.g. for the example below use

mvn enforcer:enforce@dependency-convergence

Here's a snippet from my pom;

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-enforcer-plugin</artifactId>
            <version>1.4.1</version>
            <executions>
                <execution>
                    <id>dependency-convergence</id>
                    <phase>install</phase>
                    <goals>
                        <goal>enforce</goal>
                    </goals>
                    <configuration>
                        <rules>
                            <DependencyConvergence />
                        </rules>
                        <fail>true</fail>
                    </configuration>
                </execution>
                <execution>
                    <id>default-cli</id>
                    <goals>
                        <goal>enforce</goal>
                    </goals>
                    <configuration>
                        <rules>
                            <DependencyConvergence/>
                        </rules>
                        <fail>true</fail>
                    </configuration>
                </execution>
            </executions>
        </plugin>
      ...

Answer 4

I don't know why it won't work with the config being in an execution, but this worked for me:

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-enforcer-plugin</artifactId>
            <version>1.0</version>
            <configuration>
                <rules>
                    <banDuplicateClasses>
                        <findAllDuplicates>true</findAllDuplicates>
                    </banDuplicateClasses>
                </rules>
                <fail>false</fail>
            </configuration>
            <dependencies>
                <dependency>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>extra-enforcer-rules</artifactId>
                    <version>1.0-alpha-1</version>
                </dependency>
            </dependencies>
        </plugin>