物联网 基于netty构建mqtt协议规范(遗嘱与保留消息)
简述
遗嘱消息（Last Will） 和 保留消息（Retained Message） 是两个重要的特性
- 遗嘱消息
客户端异常断开（非正常发送 DISCONNECT）时，Broker 自动发布一条预定义的消息到指定主题，通知其他客户端
- 保留消息
发布者可以标记消息为"保留"，Broker 为每个主题存储最新的保留消息。新订阅该主题的客户端会立即收到这条保留消息
源码(netty-sample-03-Last)
https://gitee.com/kcnf-iot/iot-sample/tree/master/netty/netty-sample-03
要点总结
| 特性 | 触发条件 | 存储位置 | 推送时机 |
|---|---|---|---|
| 遗嘱消息 | 客户端异常断开（Channel inactive 且未发送 DISCONNECT） | 内存中关联 Channel | 异常断开时立即发布 |
| 保留消息 | PUBLISH 命令中 retain=1 | ConcurrentHashMap<String, String> |
新订阅时立即推送（若存在） |
server代码
package com.jysemel.iot;
import com.jysemel.iot.handler.BrokerHandler;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import java.nio.charset.StandardCharsets;
public class WillRetainBroker {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new LineBasedFrameDecoder(1024));
pipeline.addLast(new StringDecoder(StandardCharsets.UTF_8));
pipeline.addLast(new StringEncoder(StandardCharsets.UTF_8));
pipeline.addLast(new BrokerHandler());
}
});
ChannelFuture future = bootstrap.bind(8888).sync();
System.out.println("╔════════════════════════════════════╗");
System.out.println("║ MQTT Broker 已启动 ║");
System.out.println("╠════════════════════════════════════╣");
System.out.println("║ 端口: 8888 ║");
System.out.println("║ 支持命令: ║");
System.out.println("║ • CONNECT - 连接（设置遗嘱） ║");
System.out.println("║ • SUB - 订阅主题 ║");
System.out.println("║ • PUB - 发布消息 ║");
System.out.println("║ • DISCONNECT - 正常断开 ║");
System.out.println("║ 核心功能: ║");
System.out.println("║ ✓ 遗嘱消息（异常断开触发） ║");
System.out.println("║ ✓ 保留消息（新订阅者立即可见） ║");
System.out.println("╚════════════════════════════════════╝");
future.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}client代码
package com.jysemel.iot;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import java.nio.charset.StandardCharsets;
public class WillRetainClient {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) {
ChannelPipeline p = ch.pipeline();
p.addLast(new LineBasedFrameDecoder(1024));
p.addLast(new StringDecoder(StandardCharsets.UTF_8));
p.addLast(new StringEncoder(StandardCharsets.UTF_8));
}
});
System.out.println("╔════════════════════════════════════╗");
System.out.println("║ MQTT 发布者客户端（演示遗嘱+保留） ║");
System.out.println("╚════════════════════════════════════╝");
System.out.println("🔌 正在连接 Broker...");
Channel channel = bootstrap.connect("127.0.0.1", 8888).sync().channel();
System.out.println("✅ 连接成功！\n");
Thread.sleep(1000);
System.out.println("━━━━━━━━━━━━ 步骤1: 设置遗嘱消息 ━━━━━━━━━━━━");
System.out.println("📝 遗嘱主题: /device/status");
System.out.println("📝 遗嘱内容: 设备离线（异常断开时触发）");
channel.writeAndFlush("CONNECT /device/status 设备离线\n").sync();
Thread.sleep(2000);
System.out.println("\n━━━━━━━━━━━━ 步骤2: 发布普通消息 ━━━━━━━━━━━━");
channel.writeAndFlush("PUB /device/status 设备在线\n").sync();
System.out.println("📤 已发布: 设备在线");
Thread.sleep(1500);
System.out.println("\n━━━━━━━━━━━━ 步骤3: 发布保留消息 ━━━━━━━━━━━━");
System.out.println("💡 特点: 新订阅者会立即收到此消息");
channel.writeAndFlush("PUB /device/status 温度:25℃ RETAINED\n").sync();
System.out.println("📤 已发布: 温度:25℃ [保留]");
Thread.sleep(3000);
System.out.println("\n━━━━━━━━━━━━ 测试说明 ━━━━━━━━━━━━");
System.out.println("✅ 现在启动 SubscriberClient，会立即收到【保留消息】");
System.out.println("⚠️ 按 Ctrl+C 强制关闭本程序，将触发【遗嘱消息】");
System.out.println("💡 遗嘱消息会发送给所有订阅了 /device/status 的客户端\n");
channel.closeFuture().sync();
} finally {
group.shutdownGracefully();
}
}
}
package com.jysemel.iot;
import com.jysemel.iot.handler.ClientHandler;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import java.nio.charset.StandardCharsets;
public class SubscriberClient {
public static void main(String[] args) throws InterruptedException {
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group)
.channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) {
ChannelPipeline p = ch.pipeline();
p.addLast(new LineBasedFrameDecoder(1024));
p.addLast(new StringDecoder(StandardCharsets.UTF_8));
p.addLast(new StringEncoder(StandardCharsets.UTF_8));
p.addLast(new ClientHandler());
}
});
System.out.println("╔════════════════════════════════════╗");
System.out.println("║ MQTT 订阅者客户端 ║");
System.out.println("╚════════════════════════════════════╝");
System.out.println("🔌 正在连接 Broker...");
Channel channel = bootstrap.connect("127.0.0.1", 8888).sync().channel();
System.out.println("✅ 连接成功！\n");
Thread.sleep(500);
System.out.println("📋 订阅主题: /device/status");
System.out.println("💡 如果该主题有保留消息，将立即收到\n");
channel.writeAndFlush("SUB /device/status\n");
System.out.println("⏳ 等待接收消息...\n");
System.out.println("💡 提示：");
System.out.println(" 1. 先运行 WillRetainClient 发布保留消息");
System.out.println(" 2. 再运行本程序，会立即收到保留消息");
System.out.println(" 3. 强制关闭 WillRetainClient 可看到遗嘱消息\n");
channel.closeFuture().sync();
} finally {
group.shutdownGracefully();
}
}
}验证结果
