Modify your project POM to look something like this:

<project ...>
            The following configuration parameters are allowed:

              sourceDir (optional)
                Directory of the source tree where source code lives.

              interfaces (mandatory)
                A set of interfaces for which proxy classes are generated.
              Add the names of proxied interfaces here...
      <name>QXS Plugin Repository</name>

Change the configuration according to your needs. Next, generate the proxy classes:

mvn generate-sources

Note that there is usually no need for calling the generate-sources target explicitly. The result will be a set of java classes whose names start with Proxy, e.g. org.example.ProxyClassName.