[JavaMan]

Попробуй так

            @Override
            protected Object decode(ChannelHandlerContext chc, Channel chnl, ChannelBuffer cb) throws Exception {
               System.out.println("ChannelBuffer content: " + cb.toString(new Charset("UTF-8")));
            }

И убери из пипелайна

pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.nulDelimiter()));