我试图弄清楚如何在HiveMQ Client中使用相同的try catch块甚至在不同的客户端中接收多条消息。我遵循以下示例：
上面的示例适用于一个客户端和单个发布和订阅，但是我想尽可能在try catch的同一块中执行多个这些操作。
package com.main;
import java.util.UUID;
import com.hivemq.client.mqtt.MqttGlobalPublishFilter;
import com.hivemq.client.mqtt.datatypes.MqttQos;
import com.hivemq.client.mqtt.mqtt5.Mqtt5BlockingClient;
import com.hivemq.client.mqtt.mqtt5.Mqtt5BlockingClient.Mqtt5Publishes;
import com.hivemq.client.mqtt.mqtt5.Mqtt5Client;
import com.hivemq.client.mqtt.mqtt5.message.publish.Mqtt5Publish;
import java.util.logging.Logger;
import java.util.NoSuchElementException;
import java.util.logging.Level;
import java.util.concurrent.TimeUnit;
public class Main {
private static final Logger LOGGER = Logger.getLogger(Main.class.getName()); // Creates a logger instance
public static void main(String[] args) {
Mqtt5BlockingClient client1 = Mqtt5Client.builder()
.identifier(UUID.randomUUID().toString()) // the unique identifier of the MQTT client. The ID is randomly generated between
.serverHost("localhost") // the host name or IP address of the MQTT server. Kept it 0.0.0.0 for testing. localhost is default if not specified.
.serverPort(1883) // specifies the port of the server
.buildBlocking(); // creates the client builder
client1.connect(); // connects the client
System.out.println("Client1 Connected");
Mqtt5BlockingClient client2 = Mqtt5Client.builder()
.identifier(UUID.randomUUID().toString()) // the unique identifier of the MQTT client. The ID is randomly generated between
.serverHost("localhost") // the host name or IP address of the MQTT server. Kept it 0.0.0.0 for testing. localhost is default if not specified.
.serverPort(1883) // specifies the port of the server
.buildBlocking(); // creates the client builder
client2.connect(); // connects the client
System.out.println("Client2 Connected");
String testmessage = "How is it going!";
byte[] messagebytesend = testmessage.getBytes(); // stores a message as a byte array to be used in the payload
try {
Mqtt5Publishes publishes = client1.publishes(MqttGlobalPublishFilter.ALL); // creates a "publishes" instance thats used to queue incoming messages
// .ALL - filters all incoming Publish messages
client1.subscribeWith() // creates a subscription
.topicFilter("test/something1/topic") // filters to receive messages only on this topic (# = Multilevel wild card, + = single level wild card)
.qos(MqttQos.AT_LEAST_ONCE) // Sets the QoS to 2 (At least once)
.send();
System.out.println("The client1 has subscribed");
client1.publishWith() // publishes the message to the subscribed topic
.topic("test/something1/topic") // publishes to the specified topic
.qos(MqttQos.AT_LEAST_ONCE)
.payload(messagebytesend) // the contents of the message
.send();
System.out.println("The client1 has published");
Mqtt5Publish receivedMessage = publishes.receive(5,TimeUnit.SECONDS).get(); // receives the message using the "publishes" instance waiting up to 5 seconds // .get() returns the object if available or throws a NoSuchElementException
byte[] tempdata = receivedMessage.getPayloadAsBytes(); // converts the "Optional" type message to a byte array
System.out.println();
String getdata = new String(tempdata); // converts the byte array to a String
System.out.println(getdata);
client2.subscribeWith() // creates a subscription
.topicFilter("test/something2/topic") // filters to receive messages only on this topic (# = Multilevel wild card, + = single level wild card)
.qos(MqttQos.AT_LEAST_ONCE) // Sets the QoS to 2 (At least once)
.send();
System.out.println("The client2 has subscribed");
client2.publishWith() // publishes the message to the subscribed topic
.topic("test/something2/topic") // publishes to the specified topic
.qos(MqttQos.AT_LEAST_ONCE)
.payload("The second message :P".getBytes()) // the contents of the message
.send();
System.out.println("The client2 has published");
System.out.println();
// VV Why isn't the publish instance below receiving the second message? Do i need another try catch? VV
receivedMessage = publishes.receive(5,TimeUnit.SECONDS).get(); // receives the message using the "publishes" instance waiting up to 5 seconds // .get() returns the object if available or throws a NoSuchElementException
byte[] tempdata2 = receivedMessage.getPayloadAsBytes(); // converts the "Optional" type message to a byte array
System.out.println();
getdata = new String(tempdata2); // converts the byte array to a String
System.out.println(getdata);
}
catch (InterruptedException e) { // Catches interruptions in the thread
LOGGER.log(Level.SEVERE, "The thread was interrupted while waiting for a message to be received", e);
}
catch (NoSuchElementException e){
System.out.println("There are no received messages"); // Handles when a publish instance has no messages
}
client1.disconnect();
System.out.println("Client1 Disconnected");
client2.disconnect();
System.out.println("Client2 Disconnected");
}
}
我得到的输出：
Client1已连接
Client2已连接
client1已订阅
client1已发布
进展如何！
client2已订阅
client2已发布
没有收到的消息
Client1已断开连接
Client2已断开连接
我想要的输出：
Client1已连接
Client2已连接
client1已订阅
client1已发布
进展如何！
client2已订阅
client2已发布
第二条消息：P
Client1已断开连接
Client2已断开连接
答案 0 :(得分：2)
我运行了您的代码，发现了此WARN日志：
2019-06-11 20:32:22,774 WARN - No publish flow registered for MqttStatefulPublish{stateless=MqttPublish{topic=test/something2/topic, payload=21byte, qos=AT_LEAST_ONCE, retain=false}, packetIdentifier=51, dup=false, topicAlias=0, subscriptionIdentifiers=[1]}.
您似乎忘记了为第二个客户端设置发布过滤器。确实在等待第二条消息（对于client2）的代码中，您检查了client1的消息流。 因此，您只需要为client2添加一个发布过滤器：
Mqtt5Publishes publishesClient2 = client2.publishes(MqttGlobalPublishFilter.ALL);
然后等待client2的消息：
// VV Why isn't the publish instance below receiving the second message? Do i need another try catch? VV
receivedMessage = publishesClient2.receive(5,TimeUnit.SECONDS).get();
结果：
之前：
Client1 Connected
Client2 Connected
The client1 has subscribed
The client1 has published
How is it going!
The client2 has subscribed
The client2 has published
2019-06-11 20:46:36,537 WARN - No publish flow registered for MqttStatefulPublish{stateless=MqttPublish{topic=test/something2/topic, payload=21byte, qos=AT_LEAST_ONCE, retain=false}, packetIdentifier=51, dup=false, topicAlias=0, subscriptionIdentifiers=[1]}.
There are no received messages
Client1 Disconnected
Client2 Disconnected
之后：
Client1 Connected
Client2 Connected
The client1 has subscribed
The client1 has published
How is it going!
The client2 has subscribed
The client2 has published
The second message :P
Client1 Disconnected
Client2 Disconnected
编辑：我希望这是您正在寻找的解决方案，因为所需的输出与通过修复获得的输出不同。由于NoSuchElementException不再抛出/捕获。因此，第二条消息丢失后，“没有收到的消息”。
根据评论进行编辑：具有异步风味的client2收集发布消息的代码段（只需将try块中的代码替换为以下代码）：
// The list where we put our received publish messages
final List<Mqtt5Publish> incomingMessagesClient2 = new LinkedList<>();
// With the async flavour we can add a consumer for the incoming publish messages
client2.toAsync().publishes(MqttGlobalPublishFilter.ALL, mqtt5Publish ->
incomingMessagesClient2.add(mqtt5Publish));
client1.publishes(MqttGlobalPublishFilter.ALL); // creates a "publishes" instance thats used to queue incoming messages
client2.subscribeWith() // creates a subscription
.topicFilter("test/something1/topic") // filters to receive messages only on this topic (# = Multilevel wild card, + = single level wild card)
.qos(MqttQos.AT_LEAST_ONCE) // Sets the QoS to 2 (At least once)
.send();
System.out.println("The client2 has subscribed");
client1.publishWith() // publishes the message to the subscribed topic
.topic("test/something1/topic") // publishes to the specified topic
.qos(MqttQos.AT_LEAST_ONCE)
.payload(messagebytesend) // the contents of the message
.send();
System.out.println("The client1 has published");
client1.publishWith() // publishes the message to the subscribed topic
.topic("test/something1/topic") // publishes to the specified topic
.qos(MqttQos.AT_LEAST_ONCE)
.payload("The second message :P".getBytes()) // the contents of the message
.send();
System.out.println("The client1 has published");
System.out.println();
TimeUnit.SECONDS.sleep(5);
incomingMessagesClient2.forEach(mqtt5Publish -> System.out.println(new String(mqtt5Publish.getPayloadAsBytes())));
最诚挚的问候，
HiveMQ团队的迈克尔