netty实现UDP多播

广播方

/**
 * 类说明：广播
 */
public class LogEventBroadcaster {
    private final EventLoopGroup group;
    private final Bootstrap bootstrap;

    public LogEventBroadcaster(InetSocketAddress remoteAddress) {
        group = new NioEventLoopGroup();
        bootstrap = new Bootstrap();
        //引导该 NioDatagramChannel（无连接的）
        bootstrap.group(group).channel(NioDatagramChannel.class)

             //设置 SO_BROADCAST 套接字选项
             .option(ChannelOption.SO_BROADCAST,true)

             .handler(new LogEventEncoder(remoteAddress));
    }

    public void run() throws Exception {
        //绑定 Channel
        Channel ch = bootstrap.bind(0).sync().channel();
        long count = 0;

        //启动主处理循环，模拟日志发送
        for (;;) {
            ch.writeAndFlush(new LogMsg(null, ++count,
                    LogConst.getLogInfo()));
            try {
                //休眠 2 秒，如果被中断，则退出循环；
                Thread.sleep(2000);

            } catch (InterruptedException e) {
                Thread.interrupted();
                break;
            }
        }
    }

    public void stop() {
        group.shutdownGracefully();
    }

    public static void main(String[] args) throws Exception {

        //创建并启动一个新的 UdpQuestionSide 的实例
        LogEventBroadcaster broadcaster = new LogEventBroadcaster(
                //表明本应用发送的报文并没有一个确定的目的地，也就是进行广播
                new InetSocketAddress("255.255.255.255",
                        LogConst.MONITOR_SIDE_PORT));
        try {
            broadcaster.run();
        }
        finally {
            broadcaster.stop();
        }
    }
}

编码器

/**
 * 类说明：编码，将实际的日志实体类编码为DatagramPacket
 */
public class LogEventEncoder extends MessageToMessageEncoder<LogMsg> {
    private final InetSocketAddress remoteAddress;

    //LogEventEncoder 创建了即将被发送到指定的 InetSocketAddress
    // 的 DatagramPacket 消息
    public LogEventEncoder(InetSocketAddress remoteAddress) {
        this.remoteAddress = remoteAddress;
    }

    @Override
    protected void encode(ChannelHandlerContext channelHandlerContext,
                          LogMsg logMsg, List<Object> out) throws Exception {
        byte[] msg = logMsg.getMsg().getBytes(CharsetUtil.UTF_8);
        //容量的计算：两个long型+消息的内容+分割符
        ByteBuf buf = channelHandlerContext.alloc()
                .buffer(8*2 + msg.length + 1);
        //将发送时间写入到 ByteBuf中
        buf.writeLong(logMsg.getTime());
        //将消息id写入到 ByteBuf中
        buf.writeLong(logMsg.getMsgId());
        //添加一个 SEPARATOR
        buf.writeByte(LogMsg.SEPARATOR);
        //将日志消息写入 ByteBuf中
        buf.writeBytes(msg);
        //将一个拥有数据和目的地地址的新 DatagramPacket 添加到出站的消息列表中
        out.add(new DatagramPacket(buf, remoteAddress));
    }
}

接收方

/**
 * 类说明：接收方
 */
public class LogEventMonitor {
    private final EventLoopGroup group;
    private final Bootstrap bootstrap;

    public LogEventMonitor(InetSocketAddress address) {
        group = new NioEventLoopGroup();
        bootstrap = new Bootstrap();
        //引导该 NioDatagramChannel
        bootstrap.group(group)
            .channel(NioDatagramChannel.class)

            //设置套接字选项 SO_BROADCAST
            .option(ChannelOption.SO_BROADCAST, true)

            //允许端口重用，可开启多个接收方
            .option(ChannelOption.SO_REUSEADDR,true)

            .handler( new ChannelInitializer<Channel>() {
                @Override
                protected void initChannel(Channel channel)
                    throws Exception {
                    ChannelPipeline pipeline = channel.pipeline();

                    pipeline.addLast(new LogEventDecoder());

                    pipeline.addLast(new LogEventHandler());
                }
            } )
            .localAddress(address);
    }

    public Channel bind() {
        //绑定 Channel。注意，DatagramChannel 是无连接的
        return bootstrap.bind().syncUninterruptibly().channel();
    }

    public void stop() {
        group.shutdownGracefully();
    }

    public static void main(String[] args) throws Exception {
        //构造一个新的 UdpAnswerSide并指明监听端口
        LogEventMonitor monitor = new LogEventMonitor(
            new InetSocketAddress(LogConst.MONITOR_SIDE_PORT));
        try {
            //绑定本地监听端口
            Channel channel = monitor.bind();
            System.out.println("UdpAnswerSide running");
            channel.closeFuture().sync();
        } finally {
            monitor.stop();
        }
    }
}

解码器

/**
 * 类说明：解码，将DatagramPacket解码为实际的日志实体类
 */
public class LogEventDecoder extends MessageToMessageDecoder<DatagramPacket> {

    @Override
    protected void decode(ChannelHandlerContext ctx,
                          DatagramPacket datagramPacket, List<Object> out)
        throws Exception {
        //获取对 DatagramPacket 中的数据（ByteBuf）的引用
        ByteBuf data = datagramPacket.content();
        //获得发送时间
        long sendTime = data.readLong();
        System.out.println("接受到"+sendTime+"发送的消息");
        //获得消息的id
        long msgId = data.readLong();
        //获得分隔符SEPARATOR
        byte sepa = data.readByte();
        //获取读索引的当前位置，就是分隔符的索引+1
        int idx = data.readerIndex();
        //提取日志消息，从读索引开始，到最后为日志的信息
        String sendMsg = data.slice(idx ,
            data.readableBytes()).toString(CharsetUtil.UTF_8);
        //构建一个新的 LogMsg 对象，并且将它添加到（已经解码的消息的）列表中
        LogMsg event = new LogMsg(datagramPacket.sender(),
                msgId, sendMsg);
        //作为本handler的处理结果，交给后面的handler进行处理
        out.add(event);
    }
}

接收方处理器

/**
 * 类说明：日志的业务处理类,实际的业务处理，接受日志信息
 */
public class LogEventHandler
    extends SimpleChannelInboundHandler<LogMsg> {

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx,
        Throwable cause) throws Exception {
        //当异常发生时，打印栈跟踪信息，并关闭对应的 Channel
        cause.printStackTrace();
        ctx.close();
    }

    @Override
    public void channelRead0(ChannelHandlerContext ctx,
        LogMsg event) throws Exception {
        //创建 StringBuilder，并且构建输出的字符串
        StringBuilder builder = new StringBuilder();
        builder.append(event.getTime());
        builder.append(" [");
        builder.append(event.getSource().toString());
        builder.append("] ：[");
        builder.append(event.getMsgId());
        builder.append("] ：");
        builder.append(event.getMsg());
        //打印 LogMsg 的数据
        System.out.println(builder.toString());
    }
}

消息实体

/**
 * 类说明：日志实体类
 */
public final class LogMsg {
    public static final byte SEPARATOR = (byte) ':';
    /*源的 InetSocketAddress*/
    private final InetSocketAddress source;
    /*消息内容*/
    private final String msg;
    /*消息id*/
    private final long msgId;
    /*消息发送或者接受的时间*/
    private final long time;

    //用于传入消息的构造函数
    public LogMsg(String msg) {
        this(null, msg,-1,System.currentTimeMillis());
    }

    //用于传出消息的构造函数
    public LogMsg(InetSocketAddress source, long msgId,
                  String msg) {
        this(source,msg,msgId,System.currentTimeMillis());
    }

    public LogMsg(InetSocketAddress source, String msg, long msgId, long time) {
        this.source = source;
        this.msg = msg;
        this.msgId = msgId;
        this.time = time;
    }

    //返回发送 LogMsg 的源的 InetSocketAddress
    public InetSocketAddress getSource() {
        return source;
    }

    //返回消息内容
    public String getMsg() {
        return msg;
    }

    //返回消息id
    public long getMsgId() {
        return msgId;
    }

    //返回消息中的时间
    public long getTime() {
        return time;
    }
}

消息工具类

/**
 * 类说明：日志信息，用String数组代替
 */
public class LogConst {
    public final static int MONITOR_SIDE_PORT = 9998;
    private static final String[] LOG_INFOS = {
            "20180912:mark-machine:Send sms to 10001",
            "20180912:lison-machine:Send email to james@enjoyedu",
            "20180912:james-machine:Happen Exception",
            "20180912:peter-machine:人生不能象做菜,把所有的料都准备好了才下锅",
            "20180912:deer-machine:牵着你的手,就象左手牵右手没感觉,但砍下去也会痛!",
            "20180912:king-machine:我听别人说这世界上有一种鸟是没有脚的," +
                    "它只能一直飞呀飞呀,飞累了就在风里面睡觉,这种鸟一辈子只能下地一次," +
                    "那一次就是它死亡的时候.",
            "20180912:mark-machine:多年以后我有个绰号叫西毒,任何人都可以变得狠毒," +
                    "只要你尝试过什么叫妒嫉.我不介意其他人怎么看我," +
                    "我只不过不想别人比我更开心.我以为有一些人永远不会妒嫉," +
                    "因为他太骄傲 . 在我出道的时候,我认识了一个人," +
                    "因为他喜欢在东边出没,所以很多年以后,他有个绰号叫东邪.",
            "20180912:lison-machine:做人如果没有梦想,那和咸鱼有什么区别",
            "20180912:james-machine:恐惧让你沦为囚犯,希望让你重获自由," +
                    "坚强的人只能救赎自己,伟大的人才能拯救别人." +
                    "记着,希望是件好东西,而且从没有一样好东西会消逝." +
                    "忙活,或者等死.",
            "20180912:peter-machine:世界上最远的距离不是生和死," +
                    "而是我站在你的面前却不能说:我爱你",
            "20180912:deer-machine:成功的含义不在于得到什么," +
                    "而是在于你从那个奋斗的起点走了多远.",
            "20180912:king-machine:一个人杀了一个人,他是杀人犯.是坏人," +
                    "当一个人杀了成千上万人后,他是英雄,是大好人",
            "20180912:mark-machine:世界在我掌握中，我却掌握不住对你的感情",
            "20180912:lison-machine:我害怕前面的路，但是一想到你，就有能力向前走了。",
            "20180912:james-machine:早就劝你别吸烟，可是烟雾中的你是那么的美，" +
                    "叫我怎么劝得下口。",
            "20180912:peter-machine:如果你只做自己能力范围之内的事情，就永远无法进步。" +
                    "昨天已成为历史，明天是未知的，而今天是上天赐予我们的礼物，" +
                    "这就是为什么我们把它叫做现在！",
            "20180912:deer-machine:年轻的时候有贼心没贼胆，等到了老了吧，" +
                    "贼心贼胆都有了，可贼又没了。",
            "20180912:king-machine:别看现在闹得欢，小心将来拉清单。"};

    private final static Random r = new Random();
    public static String getLogInfo(){
        return LOG_INFOS[r.nextInt(LOG_INFOS.length-1)];
    }
}

效果

开启一个广播方，3个接收方：