subscribe(aLong->refreshBG(context),throwable->throwable.printStackTrace());
时间: 2024-05-31 12:14:41 浏览: 73
这段代码使用了 RxJava 库来实现一个订阅操作。具体来说,该代码订阅了一个 Observable 对象,该对象的事件类型为 Long 类型,当该 Observable 发出一个事件时,会调用 refreshBG 方法来刷新背景,如果发生错误则打印错误信息。其中,context 参数表示上下文对象。
相关问题
利用netty-mqtt-client实现Mqtt消息的发布和订阅的java代码,并中文注释
以下是利用Netty-Mqtt-Client实现Mqtt消息发布和订阅的Java代码,并附有中文注释:
```
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.mqtt.*;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.util.CharsetUtil;
import java.util.concurrent.TimeUnit;
public class MqttClientHandler extends SimpleChannelInboundHandler<MqttMessage> {
private MqttClient mqttClient;
public MqttClientHandler(MqttClient mqttClient) {
this.mqttClient = mqttClient;
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
// 当连接建立成功后,发送连接消息
MqttConnectMessage connectMessage = MqttMessageBuilders.connect()
.clientId(mqttClient.getClientId())
.protocolVersion(MqttVersion.MQTT_3_1_1)
.build();
ctx.writeAndFlush(connectMessage);
}
@Override
public void channelRead0(ChannelHandlerContext ctx, MqttMessage mqttMessage) throws Exception {
// 处理收到的消息
switch (mqttMessage.fixedHeader().messageType()) {
case CONNACK:
// 当收到连接确认消息后,订阅主题
MqttSubscribeMessage subscribeMessage = MqttMessageBuilders.subscribe()
.addSubscription(MqttQoS.AT_LEAST_ONCE, mqttClient.getTopic())
.messageId(mqttClient.getNextMessageId())
.build();
ctx.writeAndFlush(subscribeMessage);
break;
case SUBACK:
// 当收到订阅确认消息后,发送消息
String message = "Hello from " + mqttClient.getClientId();
MqttPublishMessage publishMessage = MqttMessageBuilders.publish()
.topicName(mqttClient.getTopic())
.qos(MqttQoS.AT_LEAST_ONCE)
.payload(message.getBytes(CharsetUtil.UTF_8))
.messageId(mqttClient.getNextMessageId())
.build();
ctx.writeAndFlush(publishMessage);
break;
case PUBLISH:
// 当收到消息时,输出消息内容
MqttPublishMessage publish = (MqttPublishMessage) mqttMessage;
String payload = publish.payload().toString(CharsetUtil.UTF_8);
System.out.println("Received message: " + payload);
break;
default:
break;
}
}
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
// 当连接空闲时,发送心跳包
if (evt instanceof IdleStateEvent) {
IdleStateEvent event = (IdleStateEvent) evt;
if (event.state() == IdleState.WRITER_IDLE) {
MqttMessage pingReqMessage = MqttMessageBuilders.pingreq().build();
ctx.writeAndFlush(pingReqMessage);
}
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
// 当出现异常时,输出异常信息
cause.printStackTrace();
ctx.close();
}
}
```
其中,MqttClient是自定义的类,用于存储Mqtt连接相关信息,包括clientId和topic等。在channelActive方法中,发送连接消息;在channelRead0方法中,根据不同的消息类型处理收到的消息;在userEventTriggered方法中,当连接空闲时发送心跳包;在exceptionCaught方法中,处理异常。这里实现的是Mqtt发布和订阅功能,当连接建立成功后,会订阅指定的主题,然后发送一条消息,当收到消息时会输出消息内容。
用Netty-Mqtt-Client实现Mqtt发布消息和订阅消息的核心Java代码,要注释说明
好的,以下是使用Netty-Mqtt-Client实现Mqtt发布消息和订阅消息的Java代码,附有注释说明:
```java
import io.netty.handler.codec.mqtt.*;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
public class MqttClientHandler extends SimpleChannelInboundHandler<MqttMessage> {
private Channel channel;
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
super.channelActive(ctx);
channel = ctx.channel();
// 发送连接请求
MqttConnectMessage connectMessage = MqttMessageBuilders.connect()
.clientId("mqtt-client")
.cleanSession(true)
.build();
channel.writeAndFlush(connectMessage);
}
@Override
protected void channelRead0(ChannelHandlerContext ctx, MqttMessage msg) throws Exception {
// 处理接收到的消息
switch (msg.fixedHeader().messageType()) {
case CONNACK:
// 连接成功后,订阅主题
MqttSubscribeMessage subscribeMessage = MqttMessageBuilders.subscribe()
.addSubscription(MqttQoS.AT_LEAST_ONCE, "test/topic")
.build();
channel.writeAndFlush(subscribeMessage);
break;
case SUBACK:
// 订阅主题成功后,发送消息
MqttPublishMessage publishMessage = MqttMessageBuilders.publish()
.topicName("test/topic")
.qos(MqttQoS.AT_LEAST_ONCE)
.payload(Unpooled.copiedBuffer("hello, mqtt".getBytes()))
.build();
channel.writeAndFlush(publishMessage);
break;
case PUBLISH:
// 处理接收到的消息
MqttPublishMessage publishMsg = (MqttPublishMessage) msg;
System.out.println("Received message: " + publishMsg.payload().toString());
break;
default:
break;
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
super.exceptionCaught(ctx, cause);
cause.printStackTrace();
ctx.close();
}
}
```
这里的MqttClientHandler继承了Netty的SimpleChannelInboundHandler,用于处理接收到的Mqtt消息。在channelActive方法中,发送连接请求,包括设置客户端ID、清除会话等信息。在channelRead0方法中,根据接收到的消息类型进行处理,包括连接响应(CONNACK)、订阅主题(SUBACK)、接收消息(PUBLISH)等。其中,在连接响应(CONNACK)之后,发送订阅主题请求,订阅主题成功后,再发送消息到指定主题。在接收到消息(PUBLISH)时,打印消息内容。
关于注释,代码中已经加上了较为详细的注释,希望能够帮助您理解代码的实现。
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