netty tcp 改 udp

之前看了闪电侠的netty入门实战，对netty有了初步的了解。闪大的《netty 仿写IM即时通讯》是针对tcp连接的，最近做实验要搭建集群，需要使用udp广播，所以把之前的tcp通讯改为udp通讯。

tcp编解码器

    @Override
    protected void encode(ChannelHandlerContext ctx, Packet packet, List<Object> list) throws Exception {
        ByteBuf byteBuf = ctx.alloc().ioBuffer();
        PacketCodec.INSTANCE.encode(byteBuf, packet);
        list.add(byteBuf);
    }
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf byteBuf, List<Object> list) throws Exception {
       list.add((PacketCodec.INSTANCE.decode(byteBuf)));
    }

udp编解码器

    @Override
	protected void encode(ChannelHandlerContext ctx, Packet packet, List<Object> list) throws Exception {
        ByteBuf byteBuf = ctx.alloc().ioBuffer();
        PacketCodec.INSTANCE.encode(byteBuf, packet);
        list.add(new DatagramPacket(byteBuf, address));
	}
	@Override
	protected void decode(ChannelHandlerContext ctx, DatagramPacket datagramPacket, List<Object> list) throws Exception {
        Packet packet = PacketCodec.INSTANCE.decode(datagramPacket.content());
        packet.setSender(datagramPacket.sender());
        list.add(packet);
	}

udp 编解码器只需将DatagramPacket中的ByteBuf取出，然后使用之前自定义的tcp编解码器即可。

其中 PacketCodec.INSTANCE.encode(byteBuf, packet)和PacketCodec.INSTANCE.decode(byteBuf)方法如下：

    public void encode(ByteBuf byteBuf, Packet packet) {
        //1.序列 java 对象
        byte[] bytes = Serializer.DEFAULT.serialize(packet);
        //2.实际编码过程
        byteBuf.writeByte(packet.getCommand());
        byteBuf.writeInt(bytes.length);
        byteBuf.writeBytes(bytes);
    }
    public Packet decode(ByteBuf byteBuf) {
        // 1.数据包指令
        byte command = byteBuf.readByte();
        // 2.数据包长度
        int length = byteBuf.readInt();

        byte[] bytes = new byte[length];
        byteBuf.readBytes(bytes);

        Class<? extends Packet> requestType = getRequestType(command);

        Serializer serializer = Serializer.DEFAULT;

        if (requestType != null && serializer != null) {
            return serializer.deserialize(requestType, bytes);
        }

        return null;
    }

本文的代码在GitHub(https://github.com/zhangji-hhu/Netty-UDP)。

本人目前还是学生，希望各位大佬批评指正!