how to externalise the checkstyle config for maven-checkstyle-plugin

Create a separate Maven project, that contains just the Checkstyle configuration. In my case I called this project checkstyle-config and it contains the following:

checkstyle-config/src/main/resources/checkstyle.config.xml
checkstyle-config/src/main/resources/checkstyle.suppressions.xml
checkstyle-config/pom.xml

The POM file for this project is trivial:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.totaalsoftware.incidentmanager</groupId>
  <artifactId>checkstyle-config</artifactId>
  <version>2.0.0-SNAPSHOT</version>
</project>

Build it, so that it gets installed. Then use it as a dependency for your Checkstyle execution, e.g.:

  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-checkstyle-plugin</artifactId>
    <executions>
      <execution>
        <goals>
          <goal>check</goal>
        </goals>
      </execution>
    </executions>
    <dependencies>
      <dependency>
        <groupId>com.totaalsoftware.incidentmanager</groupId>
        <artifactId>checkstyle-config</artifactId>
        <version>2.0.0-SNAPSHOT</version>
      </dependency>
    </dependencies>
    <configuration>
      <configLocation>checkstyle.config.xml</configLocation>
      <suppressionsLocation>checkstyle.suppressions.xml</suppressionsLocation>

      ... other configuration ...

    </configuration>
  </plugin>

I had a similar problem. I solved it with the following configuration.

${project.basedir}/src/main/resources/checkstyle.xml

Note: my checkstyle file is located in "src/main/resources"