4.如何实现用MTQQ通过服务器实现订阅者和发布者的通讯

1.本例子意在用moquette服务器来作为消息转发，通过订阅者订阅消息，发布者发布消息，然后发布者的消息可以通过服务器转发给订阅者

服务器例子：

https://github.com/andsel/moquette

核心代码为：

    /*
 * Copyright (c) 2012-2015 The original author or authors
 * ------------------------------------------------------
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Apache License v2.0 which accompanies this distribution.
 *
 * The Eclipse Public License is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * The Apache License v2.0 is available at
 * http://www.opensource.org/licenses/apache2.0.php
 *
 * You may elect to redistribute this code under either of these licenses.
 */
package io.moquette.testembedded;

import io.moquette.interception.AbstractInterceptHandler;
import io.moquette.interception.InterceptHandler;
import io.moquette.interception.messages.*;
import io.moquette.parser.proto.messages.AbstractMessage;
import io.moquette.parser.proto.messages.PublishMessage;
import io.moquette.server.Server;
import io.moquette.server.config.IConfig;
import io.moquette.server.config.ClasspathConfig;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.List;

import static java.util.Arrays.asList;

    public class EmbeddedLauncher {
    static class PublisherListener extends AbstractInterceptHandler {

        @Override
        public void onPublish(InterceptPublishMessage msg) {
            System.out.println("Received on topic: " + msg.getTopicName() + " content: " + new String(msg.getPayload().array()));
        }
    }

    public static void main(String[] args) throws InterruptedException, IOException {
        final IConfig classPathConfig = new ClasspathConfig();

        final Server mqttBroker = new Server();
        List<? extends InterceptHandler> userHandlers = asList(new PublisherListener());
        mqttBroker.startServer(classPathConfig, userHandlers);

        System.out.println("Broker started press [CTRL+C] to stop");
        //Bind  a shutdown hook
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                System.out.println("Stopping broker");
                mqttBroker.stopServer();
                System.out.println("Broker stopped");
            }
        });

        Thread.sleep(20000);
        System.out.println("Before self publish");
        PublishMessage message = new PublishMessage();
        message.setTopicName("/exit");
        message.setRetainFlag(true);
//        message.setQos(AbstractMessage.QOSType.MOST_ONE);
//        message.setQos(AbstractMessage.QOSType.LEAST_ONE);
        message.setQos(AbstractMessage.QOSType.EXACTLY_ONCE);
        message.setPayload(ByteBuffer.wrap("Hello World!!".getBytes()));
        mqttBroker.internalPublish(message);
        System.out.println("After self publish");
    }
}

配置文件：

##############################################
#  Moquette configuration file.
#
#  The synthax is equals to mosquitto.conf
#
##############################################

port 1883

#websocket_port 8080

host 127.0.0.1

#Password file
password_file password_file.conf

#ssl_port 8883
#jks_path serverkeystore.jks
#key_store_password passw0rdsrv
#key_manager_password passw0rdsrv

allow_anonymous true

配置端口为1883，而ip为127.0.0.1

启动服务器：

效果为：

2.客户端源码

https://github.com/eclipse/paho.mqtt.java

核心代码：

1）订阅者源码

/*******************************************************************************
 * Copyright (c) 2009, 2014 IBM Corp.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 *
 * The Eclipse Public License is available at
 *    http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Dave Locke - initial API and implementation and/or initial documentation
 */

package org.eclipse.paho.sample.mqttv3app;

import java.io.IOException;
import java.sql.Timestamp;

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.persist.MqttDefaultFilePersistence;

/**
 * A sample application that demonstrates how to use the Paho MQTT v3.1 Client blocking API.
 *
 * It can be run from the command line in one of two modes:
 *  - as a publisher, sending a single message to a topic on the server
 *  - as a subscriber, listening for messages from the server
 *
 *  There are three versions of the sample that implement the same features
 *  but do so using using different programming styles:
 *  <ol>
 *  <li>Sample (this one) which uses the API which blocks until the operation completes</li>
 *  <li>SampleAsyncWait shows how to use the asynchronous API with waiters that block until
 *  an action completes</li>
 *  <li>SampleAsyncCallBack shows how to use the asynchronous API where events are
 *  used to notify the application when an action completes<li>
 *  </ol>
 *
 *  If the application is run with the -h parameter then info is displayed that
 *  describes all of the options / parameters.
 */
public class Sample implements MqttCallback {

    /**
     * The main entry point of the sample.
     *
     * This method handles parsing of the arguments specified on the
     * command-line before performing the specified action.
     */
    public static void main(String[] args) {

        // Default settings:
        boolean quietMode     = false;
        String action         = "subscribe";
        String topic         = "";
        String message         = "this is a subscriber,to subscribe message";
        int qos             = 2;
        String broker         = "127.0.0.1";
        int port             = 1883;
        String clientId     = null;
        String subTopic        = "Sample/#";
        String pubTopic     = "Sample/Java/v3";
        boolean cleanSession = true;            // Non durable subscriptions
        boolean ssl = false;
        String password = null;
        String userName = null;
        // Parse the arguments -
        for (int i=0; i<args.length; i++) {
            // Check this is a valid argument
            if (args[i].length() == 2 && args[i].startsWith("-")) {
                char arg = args[i].charAt(1);
                // Handle arguments that take no-value
                switch(arg) {
                    case 'h': case '?':    printHelp(); return;
                    case 'q': quietMode = true;    continue;
                }

                // Now handle the arguments that take a value and
                // ensure one is specified
                if (i == args.length -1 || args[i+1].charAt(0) == '-') {
                    System.out.println("Missing value for argument: "+args[i]);
                    printHelp();
                    return;
                }
                switch(arg) {
                    case 'a': action = args[++i];                 break;
                    case 't': topic = args[++i];                  break;
                    case 'm': message = args[++i];                break;
                    case 's': qos = Integer.parseInt(args[++i]);  break;
                    case 'b': broker = args[++i];                 break;
                    case 'p': port = Integer.parseInt(args[++i]); break;
                    case 'i': clientId = args[++i];                  break;
                    case 'c': cleanSession = Boolean.valueOf(args[++i]).booleanValue();  break;
                    case 'k': System.getProperties().put("javax.net.ssl.keyStore", args[++i]); break;
                    case 'w': System.getProperties().put("javax.net.ssl.keyStorePassword", args[++i]); break;
                    case 'r': System.getProperties().put("javax.net.ssl.trustStore", args[++i]); break;
                    case 'v': ssl = Boolean.valueOf(args[++i]).booleanValue(); break;
                    case 'u': userName = args[++i];               break;
                    case 'z': password = args[++i];               break;
                    default:
                        System.out.println("Unrecognised argument: "+args[i]);
                        printHelp();
                        return;
                }
            } else {
                System.out.println("Unrecognised argument: "+args[i]);
                printHelp();
                return;
            }
        }

        // Validate the provided arguments
        if (!action.equals("publish") && !action.equals("subscribe")) {
            System.out.println("Invalid action: "+action);
            printHelp();
            return;
        }
        if (qos < 0 || qos > 2) {
            System.out.println("Invalid QoS: "+qos);
            printHelp();
            return;
        }
        if (topic.equals("")) {
            // Set the default topic according to the specified action
            if (action.equals("publish")) {
                topic = pubTopic;
            } else {
                topic = subTopic;
            }
        }

        String protocol = "tcp://";

    if (ssl) {
      protocol = "ssl://";
    }

    String url = protocol + broker + ":" + port;

        if (clientId == null || clientId.equals("")) {
            clientId = "SampleJavaV3_"+action;
        }

        // With a valid set of arguments, the real work of
        // driving the client API can begin
        try {
            // Create an instance of this class
            Sample sampleClient = new Sample(url, clientId, cleanSession, quietMode,userName,password);

            // Perform the requested action
            if (action.equals("publish")) {
                sampleClient.publish(topic,qos,message.getBytes());
            } else if (action.equals("subscribe")) {
                sampleClient.subscribe(topic,qos);
            }
        } catch(MqttException me) {
            // Display full details of any exception that occurs
            System.out.println("reason "+me.getReasonCode());
            System.out.println("msg "+me.getMessage());
            System.out.println("loc "+me.getLocalizedMessage());
            System.out.println("cause "+me.getCause());
            System.out.println("excep "+me);
            me.printStackTrace();
        }
    }

    // Private instance variables
    private MqttClient             client;
    private String                 brokerUrl;
    private boolean             quietMode;
    private MqttConnectOptions     conOpt;
    private boolean             clean;
    private String password;
    private String userName;

    /**
     * Constructs an instance of the sample client wrapper
     * @param brokerUrl the url of the server to connect to
     * @param clientId the client id to connect with
     * @param cleanSession clear state at end of connection or not (durable or non-durable subscriptions)
     * @param quietMode whether debug should be printed to standard out
   * @param userName the username to connect with
   * @param password the password for the user
     * @throws MqttException
     */
    public Sample(String brokerUrl, String clientId, boolean cleanSession, boolean quietMode, String userName, String password) throws MqttException {
        this.brokerUrl = brokerUrl;
        this.quietMode = quietMode;
        this.clean        = cleanSession;
        this.password = password;
        this.userName = userName;
        //This sample stores in a temporary directory... where messages temporarily
        // stored until the message has been delivered to the server.
        //..a real application ought to store them somewhere
        // where they are not likely to get deleted or tampered with
        String tmpDir = System.getProperty("java.io.tmpdir");
        MqttDefaultFilePersistence dataStore = new MqttDefaultFilePersistence(tmpDir);

        try {
            // Construct the connection options object that contains connection parameters
            // such as cleanSession and LWT
            conOpt = new MqttConnectOptions();
            conOpt.setCleanSession(clean);
            if(password != null ) {
              conOpt.setPassword(this.password.toCharArray());
            }
            if(userName != null) {
              conOpt.setUserName(this.userName);
            }

            // Construct an MQTT blocking mode client
            client = new MqttClient(this.brokerUrl,clientId, dataStore);

            // Set this wrapper as the callback handler
            client.setCallback(this);

        } catch (MqttException e) {
            e.printStackTrace();
            log("Unable to set up client: "+e.toString());
            System.exit(1);
        }
    }

    /**
     * Publish / send a message to an MQTT server
     * @param topicName the name of the topic to publish to
     * @param qos the quality of service to delivery the message at (0,1,2)
     * @param payload the set of bytes to send to the MQTT server
     * @throws MqttException
     */
    public void publish(String topicName, int qos, byte[] payload) throws MqttException {

        // Connect to the MQTT server
        log("Connecting to "+brokerUrl + " with client ID "+client.getClientId());
        client.connect(conOpt);
        log("Connected");

        String time = new Timestamp(System.currentTimeMillis()).toString();
        log("Publishing at: "+time+ " to topic \""+topicName+"\" qos "+qos);

        // Create and configure a message
           MqttMessage message = new MqttMessage(payload);
        message.setQos(qos);

        // Send the message to the server, control is not returned until
        // it has been delivered to the server meeting the specified
        // quality of service.
        client.publish(topicName, message);

        // Disconnect the client
        client.disconnect();
        log("Disconnected");
    }

    /**
     * Subscribe to a topic on an MQTT server
     * Once subscribed this method waits for the messages to arrive from the server
     * that match the subscription. It continues listening for messages until the enter key is
     * pressed.
     * @param topicName to subscribe to (can be wild carded)
     * @param qos the maximum quality of service to receive messages at for this subscription
     * @throws MqttException
     */
    public void subscribe(String topicName, int qos) throws MqttException {

        // Connect to the MQTT server
        client.connect(conOpt);
        log("Connected to "+brokerUrl+" with client ID "+client.getClientId());

        // Subscribe to the requested topic
        // The QoS specified is the maximum level that messages will be sent to the client at.
        // For instance if QoS 1 is specified, any messages originally published at QoS 2 will
        // be downgraded to 1 when delivering to the client but messages published at 1 and 0
        // will be received at the same level they were published at.
        log("Subscribing to topic \""+topicName+"\" qos "+qos);
        client.subscribe(topicName, qos);

        // Continue waiting for messages until the Enter is pressed
        log("Press <Enter> to exit");
        try {
            System.in.read();
        } catch (IOException e) {
            //If we can't read we'll just exit
        }

        // Disconnect the client from the server
        client.disconnect();
        log("Disconnected");
    }

    /**
     * Utility method to handle logging. If 'quietMode' is set, this method does nothing
     * @param message the message to log
     */
    private void log(String message) {
        if (!quietMode) {
            System.out.println(message);
        }
    }

    /****************************************************************/
    /* Methods to implement the MqttCallback interface              */
    /****************************************************************/

    /**
     * @see MqttCallback#connectionLost(Throwable)
     */
    public void connectionLost(Throwable cause) {
        // Called when the connection to the server has been lost.
        // An application may choose to implement reconnection
        // logic at this point. This sample simply exits.
        log("Connection to " + brokerUrl + " lost!" + cause);
        System.exit(1);
    }

    /**
     * @see MqttCallback#deliveryComplete(IMqttDeliveryToken)
     */
    public void deliveryComplete(IMqttDeliveryToken token) {
        // Called when a message has been delivered to the
        // server. The token passed in here is the same one
        // that was passed to or returned from the original call to publish.
        // This allows applications to perform asynchronous
        // delivery without blocking until delivery completes.
        //
        // This sample demonstrates asynchronous deliver and
        // uses the token.waitForCompletion() call in the main thread which
        // blocks until the delivery has completed.
        // Additionally the deliveryComplete method will be called if
        // the callback is set on the client
        //
        // If the connection to the server breaks before delivery has completed
        // delivery of a message will complete after the client has re-connected.
        // The getPendingTokens method will provide tokens for any messages
        // that are still to be delivered.
    }

    /**
     * @see MqttCallback#messageArrived(String, MqttMessage)
     */
    public void messageArrived(String topic, MqttMessage message) throws MqttException {
        // Called when a message arrives from the server that matches any
        // subscription made by the client
        String time = new Timestamp(System.currentTimeMillis()).toString();
        System.out.println("Time:\t" +time +
                           "  Topic:\t" + topic +
                           "  Message:\t" + new String(message.getPayload()) +
                           "  QoS:\t" + message.getQos());
    }

    /****************************************************************/
    /* End of MqttCallback methods                                  */
    /****************************************************************/

       static void printHelp() {
          System.out.println(
              "Syntax:\n\n" +
                  "    Sample [-h] [-a publish|subscribe] [-t <topic>] [-m <message text>]\n" +
                  "            [-s 0|1|2] -b <hostname|IP address>] [-p <brokerport>] [-i <clientID>]\n\n" +
                  "    -h  Print this help text and quit\n" +
                  "    -q  Quiet mode (default is false)\n" +
                  "    -a  Perform the relevant action (default is publish)\n" +
                  "    -t  Publish/subscribe to <topic> instead of the default\n" +
                  "            (publish: \"Sample/Java/v3\", subscribe: \"Sample/#\")\n" +
                  "    -m  Use <message text> instead of the default\n" +
                  "            (\"Message from MQTTv3 Java client\")\n" +
                  "    -s  Use this QoS instead of the default (2)\n" +
                  "    -b  Use this name/IP address instead of the default (m2m.eclipse.org)\n" +
                  "    -p  Use this port instead of the default (1883)\n\n" +
                  "    -i  Use this client ID instead of SampleJavaV3_<action>\n" +
                  "    -c  Connect to the server with a clean session (default is false)\n" +
                  "     \n\n Security Options \n" +
                  "     -u Username \n" +
                  "     -z Password \n" +
                  "     \n\n SSL Options \n" +
                  "    -v  SSL enabled; true - (default is false) " +
                  "    -k  Use this JKS format key store to verify the client\n" +
                  "    -w  Passpharse to verify certificates in the keys store\n" +
                  "    -r  Use this JKS format keystore to verify the server\n" +
                  " If javax.net.ssl properties have been set only the -v flag needs to be set\n" +
                  "Delimit strings containing spaces with \"\"\n\n" +
                  "Publishers transmit a single message then disconnect from the server.\n" +
                  "Subscribers remain connected to the server and receive appropriate\n" +
                  "messages until <enter> is pressed.\n\n"
              );
    }

}

客户端-发布者

只需在configutation里面修改传入的参数即可：

为保证是同一个主题，则需要保证传入-a -t两个参数

-a subscribe -t Sample/Java/v3

最终运行结果：

服务器

订阅者：

发布者