You don't have to put an XmlRpcBean annotation to every bean you like to transfer. XmlRpc-Delight can use any unknown type as XmlRpcBean by setting

XmlRpc.XmlRpc.treatUnknownTypesAsBeans( true );

Also you can pass null-values as method arguments by setting

XmlRpc.useAutomaticNullMasking( true );

This has to be done on both server and client side.

public interface Api
{
    enum Size { tiny, medium, huge }
    
    class Bean
    {
        private Size size;
        private String[] content;
        
        public Size getSize()
        {
            return size;
        }
        
        public void setSize( Size size )
        {
            this.size = size;
        }
        
        public String[] getContent()
        {
            return content;
        }
        
        public void setContent( String[] content )
        {
            this.content = content;
        }
        
        @Override
        public String toString()
        {
            return "Bean(" + getSize() + "):" + Arrays.toString( getContent() );
        }
    }
    
    void updateBean( Bean b );
}

...
       //start server
        XmlRpc.treatUnknownTypesAsBeans( true );
        XmlRpc.useAutomaticNullMasking( true );
        StartXmlRpcServer.startXmlRpcServer( new ApiHandler() );

        //create a (remote) client to the API
        Api api = createClient( Api.class );

        //do some calls
        Api.Bean bean = new Api.Bean();
        bean.setSize( Size.medium );
        bean.setContent( new String[]{ "a", "b", "c" } );
        
        api.updateBean( bean );
        
        //also null values allowed
        Api.Bean bean2 = new Api.Bean();
        bean2.setSize( Size.tiny );
        bean2.setContent( null );
        
        api.updateBean( bean2 );
...

Examples in source code: ​http://delight.opendfki.de/repos/trunk/delight-examples/src/main/java/de/dfki/util/xmlrpc/examples/no_annontations