coap编解码器
//encode
CoapPacket coapPacket = new CoapPacket();
coapPacket.setCode(Code.C205_CONTENT);
coapPacket.setPayload("{}");
coapPacket.headers().setContentFormat(MediaTypes.CT_TEXT_PLAIN);
coapPacket.writeTo(outputStream);
//decode
CoapPacket packet = CoapPacket.deserialize(inputStream);
packet.headers();
packet.getPayloadString();