title: Add explicit source directory in jaxb2-maven-plugin for schemagen
body: <p>I would like to generate schema from JAXB annotated classes. For this, I am using jaxb2-maven-plugin. The plugin by default scans src/main/java folder for included sources. I would like to specify an extra folder to scan for java classes which is not maven source path. </p>
  
  <p>Can anyone please help?</p>
  
  <pre><code>  &lt;plugin&gt;
          &lt;groupId&gt;org.codehaus.mojo&lt;/groupId&gt;
          &lt;artifactId&gt;jaxb2-maven-plugin&lt;/artifactId&gt;
          &lt;version&gt;${maven.plugin.jaxb2}&lt;/version&gt;
          &lt;executions&gt;
             &lt;execution&gt;
                &lt;id&gt;schemagen&lt;/id&gt;
                &lt;goals&gt;
                   &lt;goal&gt;schemagen&lt;/goal&gt;
                &lt;/goals&gt;
                &lt;phase&gt;process-classes&lt;/phase&gt;
                &lt;configuration&gt;
  
                   &lt;includes&gt;
                      &lt;include&gt;SomeFolderWhichIsNotInMavenSourcePath/*.java&lt;/include&gt;
                   &lt;/includes&gt;
                   &lt;outputDirectory&gt;${project.build.directory}/schemas&lt;/outputDirectory&gt;
                &lt;/configuration&gt;
             &lt;/execution&gt;
          &lt;/executions&gt;
       &lt;/plugin&gt; 
  </code></pre>