在java中如何使用MQTT？java中的MQTT实现全面教程

如今的互联网已经朝着物联网时代埋进了，而要在物联网中进行开发，MQTT协议是绕不开的一环。今天icode9小编将为大家带来基于JAVA的MQTT协议开发操作，包括在Java项目中使用MQTT实现客户端与broker之间的连接、订阅、取消订阅、发布、接收消息等功能。大家一起来看看吧

添加依赖

本文的开发环境为：

• 构建工具：Maven

• 集成开发环境：IntelliJ IDEA

• Java：JDK 1.8.0

我们将使用Eclipse Paho Java Client作为客户端，它是 Java 语言中使用最广泛的 MQTT 客户端库。

将以下依赖项添加到pom.xml文件中。

org.eclipse.pahoorg.eclipse.paho.client.mqttv31.2.5" data-lang="" style="box-sizing: border-box;">

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

创建 MQTT 连接

MQTT 代理

本文将使用基于EMQX Cloud创建的公共 MQTT 服务器。服务器访问信息如下：

• 经纪商：broker.emqx.io

• TCP端口：1883

• SSL/TLS 端口：8883

连接

设置MQTT的基本连接参数。用户名和密码是可选的。

String broker = "tcp://broker.emqx.io:1883"; // TLS/SSL // String broker = "ssl://broker.emqx.io:8883"; String username = "emqx"; String password = "public"; String clientid = "publish_client";

然后创建一个 MQTT 客户端并连接到代理。

MqttClient client = new MqttClient(broker, clientid, new MemoryPersistence()); MqttConnectOptions options = new MqttConnectOptions(); options.setUserName(username); options.setPassword(password.toCharArray()); client.connect(options);

指示：

• MqttClient：MqttClient 提供了一组方法，一旦 MQTT 操作完成，这些方法就会阻止并将控制权返回给应用程序。

• MqttClientPersistence：表示一个持久性数据存储，用于存储传输中的出站和入站消息，从而实现指定 QoS 的交付。

• MqttConnectOptions：包含控制客户端如何连接到服务器的选项集。下面是一些常用的方法：

  • setUserName：设置用于连接的用户名。

  • setPassword：设置用于连接的密码。

  • setCleanSession：设置客户端和服务器是否应该在重新启动和重新连接时记住状态。

  • setKeepAliveInterval：设置“保持活动”间隔。

  • setConnectionTimeout：设置连接超时值。

  • setAutomaticReconnect：设置如果连接丢失，客户端是否会自动尝试重新连接到服务器。

使用 TLS/SSL 连接

如果要为 TLS/SSL 连接使用自签名证书，请将bcpkix-jdk15on添加到pom.xml文件中。

org.bouncycastlebcpkix-jdk15on1.70" data-lang="" style="box-sizing: border-box;">

<!-- https://mvnrepository.com/artifact/org.bouncycastle/bcpkix-jdk15on --> <dependency>    <groupId>org.bouncycastle</groupId>    <artifactId>bcpkix-jdk15on</artifactId>    <version>1.70</version> </dependency>

然后SSLUtils.java使用以下代码创建文件。

0) { caCert = (X509Certificate) cf.generateCertificate(bis); } // load client certificate bis = new BufferedInputStream(new FileInputStream(crtFile)); X509Certificate cert = null; while (bis.available() > 0) { cert = (X509Certificate) cf.generateCertificate(bis); } // load client private key PEMParser pemParser = new PEMParser(new FileReader(keyFile)); Object object = pemParser.readObject(); JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider("BC"); KeyPair key = converter.getKeyPair((PEMKeyPair) object); pemParser.close(); // CA certificate is used to authenticate server KeyStore caKs = KeyStore.getInstance(KeyStore.getDefaultType()); caKs.load(null, null); caKs.setCertificateEntry("ca-certificate", caCert); TrustManagerFactory tmf = TrustManagerFactory.getInstance("X509"); tmf.init(caKs); // client key and certificates are sent to server so it can authenticate KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType()); ks.load(null, null); ks.setCertificateEntry("certificate", cert); ks.setKeyEntry("private-key", key.getPrivate(), password.toCharArray(), new java.security.cert.Certificate[]{cert}); KeyManagerFactory kmf = KeyManagerFactory.getInstance(KeyManagerFactory .getDefaultAlgorithm()); kmf.init(ks, password.toCharArray()); // finally, create SSL socket factory SSLContext context = SSLContext.getInstance("TLSv1.2"); context.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null); return context.getSocketFactory(); } }" data-lang="" style="box-sizing: border-box;">

package io.emqx.mqtt;  import org.bouncycastle.jce.provider.BouncyCastleProvider; import org.bouncycastle.openssl.PEMKeyPair; import org.bouncycastle.openssl.PEMParser; import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;  import javax.net.ssl.KeyManagerFactory; import javax.net.ssl.SSLContext; import javax.net.ssl.SSLSocketFactory; import javax.net.ssl.TrustManagerFactory; import java.io.BufferedInputStream; import java.io.FileInputStream; import java.io.FileReader; import java.security.KeyPair; import java.security.KeyStore; import java.security.Security; import java.security.cert.CertificateFactory; import java.security.cert.X509Certificate;  public class SSLUtils {    public static SSLSocketFactory getSocketFactory(final String caCrtFile,                                                    final String crtFile, final String keyFile, final String password)            throws Exception {        Security.addProvider(new BouncyCastleProvider());         // load CA certificate        X509Certificate caCert = null;         FileInputStream fis = new FileInputStream(caCrtFile);        BufferedInputStream bis = new BufferedInputStream(fis);        CertificateFactory cf = CertificateFactory.getInstance("X.509");         while (bis.available() > 0) {            caCert = (X509Certificate) cf.generateCertificate(bis);       }         // load client certificate        bis = new BufferedInputStream(new FileInputStream(crtFile));        X509Certificate cert = null;        while (bis.available() > 0) {            cert = (X509Certificate) cf.generateCertificate(bis);       }         // load client private key        PEMParser pemParser = new PEMParser(new FileReader(keyFile));        Object object = pemParser.readObject();        JcaPEMKeyConverter converter = new JcaPEMKeyConverter().setProvider("BC");        KeyPair key = converter.getKeyPair((PEMKeyPair) object);        pemParser.close();         // CA certificate is used to authenticate server        KeyStore caKs = KeyStore.getInstance(KeyStore.getDefaultType());        caKs.load(null, null);        caKs.setCertificateEntry("ca-certificate", caCert);        TrustManagerFactory tmf = TrustManagerFactory.getInstance("X509");        tmf.init(caKs);         // client key and certificates are sent to server so it can authenticate        KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());        ks.load(null, null);        ks.setCertificateEntry("certificate", cert);        ks.setKeyEntry("private-key", key.getPrivate(), password.toCharArray(),                new java.security.cert.Certificate[]{cert});        KeyManagerFactory kmf = KeyManagerFactory.getInstance(KeyManagerFactory               .getDefaultAlgorithm());        kmf.init(ks, password.toCharArray());         // finally, create SSL socket factory        SSLContext context = SSLContext.getInstance("TLSv1.2");        context.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null);         return context.getSocketFactory();   } }

设置options如下。

String broker = "ssl://broker.emqx.io:8883"; // Set socket factory String caFilePath = "/cacert.pem"; String clientCrtFilePath = "/client.pem"; String clientKeyFilePath = "/client.key"; SSLSocketFactory socketFactory = getSocketFactory(caFilePath, clientCrtFilePath, clientKeyFilePath, ""); options.setSocketFactory(socketFactory);

发布 MQTT 消息

创建一个PublishSample将向主题发布Hello MQTT消息的类mqtt/test。

package io.emqx.mqtt;  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.MemoryPersistence;  public class PublishSample {     public static void main(String[] args) {         String broker = "tcp://broker.emqx.io:1883";        String topic = "mqtt/test";        String username = "emqx";        String password = "public";        String clientid = "publish_client";        String content = "Hello MQTT";        int qos = 0;         try {            MqttClient client = new MqttClient(broker, clientid, new MemoryPersistence());            MqttConnectOptions options = new MqttConnectOptions();            options.setUserName(username);            options.setPassword(password.toCharArray());            options.setConnectionTimeout(60);       options.setKeepAliveInterval(60);            // connect            client.connect(options);            // create message and setup QoS            MqttMessage message = new MqttMessage(content.getBytes());            message.setQos(qos);            // publish message            client.publish(topic, message);            System.out.println("Message published");            System.out.println("topic: " + topic);            System.out.println("message content: " + content);            // disconnect            client.disconnect();            // close client            client.close();       } catch (MqttException e) {            throw new RuntimeException(e);       }   } }

订阅

创建一个SubscribeSample将订阅主题的类mqtt/test。

package io.emqx.mqtt;  import org.eclipse.paho.client.mqttv3.*; import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;  public class SubscribeSample {    public static void main(String[] args) {        String broker = "tcp://broker.emqx.io:1883";        String topic = "mqtt/test";        String username = "emqx";        String password = "public";        String clientid = "subscribe_client";        int qos = 0;         try {            MqttClient client = new MqttClient(broker, clientid, new MemoryPersistence());            // connect options            MqttConnectOptions options = new MqttConnectOptions();            options.setUserName(username);            options.setPassword(password.toCharArray());            options.setConnectionTimeout(60);       options.setKeepAliveInterval(60);            // setup callback            client.setCallback(new MqttCallback() {                 public void connectionLost(Throwable cause) {                    System.out.println("connectionLost: " + cause.getMessage());               }                 public void messageArrived(String topic, MqttMessage message) {                    System.out.println("topic: " + topic);                    System.out.println("Qos: " + message.getQos());                    System.out.println("message content: " + new String(message.getPayload()));                }                 public void deliveryComplete(IMqttDeliveryToken token) {                    System.out.println("deliveryComplete---------" + token.isComplete());               }            });            client.connect(options);            client.subscribe(topic, qos);       } catch (Exception e) {            e.printStackTrace();       }   } }

Mqtt回调：

• connectionLost(Throwable cause)：当与服务器的连接丢失时调用此方法。

• messageArrived(String topic, MqttMessage message)：当消息从服务器到达时调用此方法。

• deliveryComplete(IMqttDeliveryToken token)：当消息的传递已完成并且已收到所有确认时调用。

测试

接下来，运行SubscribeSample订阅mqtt/test主题。然后运行PublishSample发布关于mqtt/test主题的消息。我们会看到发布者成功发布了消息，订阅者收到了消息。

至此我们就完成了使用Paho Java Client作为MQTT客户端连接公共MQTT服务器，实现消息的发布和订阅。更多的内容来自于icode9技术文章分享网站。

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