EMQX 入门实战(2)--MQTT Java 客户端库使用

Eclipse Paho Java Client 是用 Java 编写的 MQTT 客户端库（MQTT Java Client），可用于 JVM 或其他 Java 兼容平台（例如Android）；本文主要介绍使用如何使用它来操作 EMQX，文中所使用到的软件版本：EMQX 4.2.2、Paho 1.2.5、Java 1.8.0_321。

1、引入依赖

<dependency>
    <groupId>org.eclipse.paho</groupId>
    <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
    <version>1.2.5</version>
</dependency>

2、同步方式收发消息

2.1、发送消息

public static void publish() {
    try {
        MqttClient mqttClient = new MqttClient(SERVER_URI, "client-publish", new MemoryPersistence());
        MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
        /*会话清除标识
         * false:服务端必须使用与 Client ID 关联的会话来恢复与客户端的通信。如果不存在这样的会话，服务器必须创建一个新会话。客户端和服务器在断开连接后必须存储会话的状态。
         * true:客户端和服务器必须丢弃任何先前的会话并创建一个新的会话。该会话的生命周期将和网络连接保持一致，其会话状态一定不能被之后的任何会话重用。
         */
        mqttConnectOptions.setCleanSession(true);
        mqttConnectOptions.setUserName("admin");
        mqttConnectOptions.setPassword("123456".toCharArray());
        mqttConnectOptions.setKeepAliveInterval(10);
        mqttClient.setCallback(new MqttCallback() {
            @Override
            public void connectionLost(Throwable cause) {
                logger.info("连接断开:{}", cause.getMessage());
            }

            @Override
            public void messageArrived(String topic, MqttMessage message) throws Exception {
            }

            @Override
            public void deliveryComplete(IMqttDeliveryToken token) {
                logger.info("发送完成:{}", token.isComplete());
            }
        });
        mqttClient.connect(mqttConnectOptions);
        for (int i = 0; i < 10; i++) {
            MqttMessage mqttMessage = new MqttMessage(("测试消息" + (i + 1)).getBytes());
            mqttMessage.setQos(2);
            //是否保留消息，只能保留最新的一份
            mqttMessage.setRetained(false);
            mqttClient.publish(TOPIC_NAME, mqttMessage);
        }

        mqttClient.disconnect();
        mqttClient.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

2.2、接受消息

public static void subscribe(String clientId) {
    try {
        MqttClient mqttClient = new MqttClient(SERVER_URI, clientId, new MemoryPersistence());
        MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
        //设为 false, 该订阅将被视为持久订阅
        mqttConnectOptions.setCleanSession(true);
        mqttConnectOptions.setUserName("admin");
        mqttConnectOptions.setPassword("123456".toCharArray());
        mqttClient.setCallback(new MqttCallback() {
            @Override
            public void connectionLost(Throwable cause) {
                logger.info("连接断开:{}", cause.getMessage());
            }

            @Override
            public void messageArrived(String topic, MqttMessage message) throws Exception {
                logger.info("接受到消息:clientId={},topic={},message={},isRetained={}", clientId, topic, message.toString(), message.isRetained());
            }

            @Override
            public void deliveryComplete(IMqttDeliveryToken token) {
            }
        });
        mqttClient.connect(mqttConnectOptions);
        mqttClient.subscribe(TOPIC_NAME);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

2.3、完整例子

package com.abc.demo.emqx;

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MqttClientCase {
    private static Logger logger = LoggerFactory.getLogger(MqttClientCase.class.getName());
    
    private static final String SERVER_URI = "tcp://10.49.196.10:1883";
    private static final String TOPIC_NAME = "test-topic";

    public static void main(String[] args) throws Exception {
        new Thread(() -> subscribe("client-subscribe-A")).start();
        new Thread(() -> subscribe("client-subscribe-B")).start();
        Thread.sleep(1000);
        new Thread(() -> publish()).start();

        Thread.sleep(1000 * 60);
    }

    public static void publish() {
        try {
            MqttClient mqttClient = new MqttClient(SERVER_URI, "client-publish", new MemoryPersistence());
            MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
            /*会话清除标识
             * false:服务端必须使用与 Client ID 关联的会话来恢复与客户端的通信。如果不存在这样的会话，服务器必须创建一个新会话。客户端和服务器在断开连接后必须存储会话的状态。
             * true:客户端和服务器必须丢弃任何先前的会话并创建一个新的会话。该会话的生命周期将和网络连接保持一致，其会话状态一定不能被之后的任何会话重用。
             */
            mqttConnectOptions.setCleanSession(true);
            mqttConnectOptions.setUserName("admin");
            mqttConnectOptions.setPassword("123456".toCharArray());
            mqttConnectOptions.setKeepAliveInterval(10);
            mqttClient.setCallback(new MqttCallback() {
                @Override
                public void connectionLost(Throwable cause) {
                    logger.info("连接断开:{}", cause.getMessage());
                }

                @Override
                public void messageArrived(String topic, MqttMessage message) throws Exception {
                }

                @Override
                public void deliveryComplete(IMqttDeliveryToken token) {
                    logger.info("发送完成:{}", token.isComplete());
                }
            });
            mqttClient.connect(mqttConnectOptions);
            for (int i = 0; i < 10; i++) {
                MqttMessage mqttMessage = new MqttMessage(("测试消息" + (i + 1)).getBytes());
                mqttMessage.setQos(2);
                //是否保留消息，只能保留最新的一份
                mqttMessage.setRetained(false);
                mqttClient.publish(TOPIC_NAME, mqttMessage);
            }

            mqttClient.disconnect();
            mqttClient.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void subscribe(String clientId) {
        try {
            MqttClient mqttClient = new MqttClient(SERVER_URI, clientId, new MemoryPersistence());
            MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
            //设为 false, 该订阅将被视为持久订阅
            mqttConnectOptions.setCleanSession(true);
            mqttConnectOptions.setUserName("admin");
            mqttConnectOptions.setPassword("123456".toCharArray());
            mqttClient.setCallback(new MqttCallback() {
                @Override
                public void connectionLost(Throwable cause) {
                    logger.info("连接断开:{}", cause.getMessage());
                }

                @Override
                public void messageArrived(String topic, MqttMessage message) throws Exception {
                    logger.info("接受到消息:clientId={},topic={},message={},isRetained={}", clientId, topic, message.toString(), message.isRetained());
                }

                @Override
                public void deliveryComplete(IMqttDeliveryToken token) {
                }
            });
            mqttClient.connect(mqttConnectOptions);
            mqttClient.subscribe(TOPIC_NAME);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

3、异步方式收发消息

3.1、发送消息

public static void publish() {
    try {
        MqttAsyncClient mqttClient = new MqttAsyncClient(SERVER_URI, "client-publish", new MemoryPersistence());
        MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
        /*会话清除标识
         * false:服务端必须使用与 Client ID 关联的会话来恢复与客户端的通信。如果不存在这样的会话，服务器必须创建一个新会话。客户端和服务器在断开连接后必须存储会话的状态。
         * true:客户端和服务器必须丢弃任何先前的会话并创建一个新的会话。该会话的生命周期将和网络连接保持一致，其会话状态一定不能被之后的任何会话重用。
         */
        mqttConnectOptions.setCleanSession(true);
        mqttConnectOptions.setUserName("admin");
        mqttConnectOptions.setPassword("123456".toCharArray());
        mqttConnectOptions.setKeepAliveInterval(10);
        mqttClient.setCallback(new MqttCallback() {
            @Override
            public void connectionLost(Throwable cause) {
                logger.info("连接断开:{}", cause.getMessage());
            }

            @Override
            public void messageArrived(String topic, MqttMessage message) throws Exception {
            }

            @Override
            public void deliveryComplete(IMqttDeliveryToken token) {
                logger.info("发送完成:{}", token.isComplete());
            }
        });
        IMqttToken iMqttToken = mqttClient.connect(mqttConnectOptions);
        iMqttToken.waitForCompletion();
        for (int i = 0; i < 10; i++) {
            MqttMessage mqttMessage = new MqttMessage(("测试消息" + (i + 1)).getBytes());
            mqttMessage.setQos(2);
            //是否保留消息，只能保留最新的一份
            mqttMessage.setRetained(false);
            IMqttDeliveryToken iMqttDeliveryToken = mqttClient.publish(TOPIC_NAME, mqttMessage);
            iMqttDeliveryToken.waitForCompletion();
        }

        mqttClient.disconnect().waitForCompletion();
        mqttClient.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

3.2、接受消息

public static void subscribe(String clientId) {
    try {
        MqttAsyncClient mqttClient = new MqttAsyncClient(SERVER_URI, clientId, new MemoryPersistence());
        MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
        //设为 false, 该订阅将被视为持久订阅
        mqttConnectOptions.setCleanSession(true);
        mqttConnectOptions.setUserName("admin");
        mqttConnectOptions.setPassword("123456".toCharArray());
        mqttClient.setCallback(new MqttCallback() {
            @Override
            public void connectionLost(Throwable cause) {
                logger.info("连接断开:{}", cause.getMessage());
            }

            @Override
            public void messageArrived(String topic, MqttMessage message) throws Exception {
                logger.info("接受到消息:clientId={},topic={},message={},isRetained={}", clientId, topic, message.toString(), message.isRetained());
            }

            @Override
            public void deliveryComplete(IMqttDeliveryToken token) {
            }
        });
        IMqttToken iMqttToken = mqttClient.connect(mqttConnectOptions);
        iMqttToken.waitForCompletion();
        mqttClient.subscribe(TOPIC_NAME, 2).waitForCompletion();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

3.2、完整例子

package com.abc.demo.emqx;

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MqttAsyncClientCase {
    private static Logger logger = LoggerFactory.getLogger(MqttAsyncClientCase.class.getName());

    private static final String SERVER_URI = "tcp://10.49.196.10:1883";
    private static final String TOPIC_NAME = "test-topic";

    public static void main(String[] args) throws Exception {
        new Thread(() -> subscribe("client-subscribe-A")).start();
        new Thread(() -> subscribe("client-subscribe-B")).start();
        Thread.sleep(1000);
        new Thread(() -> publish()).start();

        Thread.sleep(1000 * 60);
    }

    public static void publish() {
        try {
            MqttAsyncClient mqttClient = new MqttAsyncClient(SERVER_URI, "test-client-publish", new MemoryPersistence());
            MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
            /*会话清除标识
             * false:服务端必须使用与 Client ID 关联的会话来恢复与客户端的通信。如果不存在这样的会话，服务器必须创建一个新会话。客户端和服务器在断开连接后必须存储会话的状态。
             * true:客户端和服务器必须丢弃任何先前的会话并创建一个新的会话。该会话的生命周期将和网络连接保持一致，其会话状态一定不能被之后的任何会话重用。
             */
            mqttConnectOptions.setCleanSession(true);
            mqttConnectOptions.setUserName("admin");
            mqttConnectOptions.setPassword("123456".toCharArray());
            mqttConnectOptions.setKeepAliveInterval(10);
            mqttClient.setCallback(new MqttCallback() {
                @Override
                public void connectionLost(Throwable cause) {
                    logger.info("连接断开:{}", cause.getMessage());
                }

                @Override
                public void messageArrived(String topic, MqttMessage message) throws Exception {
                }

                @Override
                public void deliveryComplete(IMqttDeliveryToken token) {
                    logger.info("发送完成:{}", token.isComplete());
                }
            });
            IMqttToken iMqttToken = mqttClient.connect(mqttConnectOptions);
            iMqttToken.waitForCompletion();
            for (int i = 0; i < 10; i++) {
                MqttMessage mqttMessage = new MqttMessage(("测试消息" + (i + 1)).getBytes());
                mqttMessage.setQos(2);
                //是否保留消息，只能保留最新的一份
                mqttMessage.setRetained(false);
                IMqttDeliveryToken iMqttDeliveryToken = mqttClient.publish(TOPIC_NAME, mqttMessage);
                iMqttDeliveryToken.waitForCompletion();
            }

            mqttClient.disconnect().waitForCompletion();
            mqttClient.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void subscribe(String clientId) {
        try {
            MqttAsyncClient mqttClient = new MqttAsyncClient(SERVER_URI, clientId, new MemoryPersistence());
            MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
            //设为 false, 该订阅将被视为持久订阅
            mqttConnectOptions.setCleanSession(true);
            mqttConnectOptions.setUserName("admin");
            mqttConnectOptions.setPassword("123456".toCharArray());
            mqttClient.setCallback(new MqttCallback() {
                @Override
                public void connectionLost(Throwable cause) {
                    logger.info("连接断开:{}", cause.getMessage());
                }

                @Override
                public void messageArrived(String topic, MqttMessage message) throws Exception {
                    logger.info("接受到消息:clientId={},topic={},message={},isRetained={}", clientId, topic, message.toString(), message.isRetained());
                }

                @Override
                public void deliveryComplete(IMqttDeliveryToken token) {
                }
            });
            IMqttToken iMqttToken = mqttClient.connect(mqttConnectOptions);
            iMqttToken.waitForCompletion();
            mqttClient.subscribe(TOPIC_NAME, 2).waitForCompletion();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}