How to configure encoding in Maven?

OK, I have found the problem.

I use some reporting plugins. In the documentation of the failsafe-maven-plugin I found, that the <encoding> configuration – of course – uses ${project.reporting.outputEncoding} by default.

So I added the property as a child element of the project element and everything is fine now:

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
</properties>

See also http://maven.apache.org/general.html#encoding-warning