set serializer => 'JSON';

hook after => sub{
    if (request->params->{format} eq 'xml'){
          send_as XML => "dsfsdf",{ content_type => 'application/xml; charset=UTF-8' };
    }
    #else return the response in json format
}

##</code><code>##

 Exception caught in 'core.app.after_request' filter: Hook error: Can't use string ("") as a subroutine ref while "strict refs" in use at /usr/local/share/perl5/Dancer2/Core/App.pm line 1103.
 at /usr/local/share/perl5/Dancer2/Core/App.pm line 36. in /usr/local/share/perl5/Dancer2/Core/App.pm l. 676