关于物联网:如何在-Java-中使用-MQTT

MQTT 是一种基于公布 / 订阅模式的 轻量级物联网音讯传输协定 ，可在重大受限的硬件设施和低带宽、高提早的网络上实现稳固传输。它凭借简略易实现、反对 QoS、报文小等特点，占据了物联网协定的半壁江山。

本文次要介绍如何在 Java 我的项目中应用 MQTT，实现客户端与服务器的连贯、订阅和收发音讯等性能。

本文的开发环境为：

构建工具：Maven
IDE：IntelliJ IDEA
Java 版本：JDK 1.8.0

本文将应用 Eclipse Paho Java Client 作为客户端，该客户端是 Java 语言中应用最为宽泛的 MQTT 客户端库。

增加以下依赖到我的项目 pom.xml 文件中。

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

本文将应用 EMQX 提供的收费公共 MQTT 服务器，该服务基于 EMQX 的 MQTT 云平台创立。服务器接入信息如下：

Broker: broker.emqx.io（中国用户能够应用 broker-cn.emqx.io）
TCP Port: 1883
SSL/TLS Port: 8883

设置 MQTT Broker 根本连贯参数，用户名、明码为非必选参数。

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";

而后创立 MQTT 客户端并连贯。

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

阐明

MqttClient: 同步调用客户端，应用阻塞办法通信。
MqttClientPersistence: 代表一个长久的数据存储，用于在传输过程中存储出站和入站的信息，使其可能传递到指定的 QoS。
MqttConnectOptions: 连贯选项，用于指定连贯的参数，上面列举一些常见的办法。
- setUserName: 设置用户名
- setPassword: 设置明码
- setCleanSession: 设置是否革除会话
- setKeepAliveInterval: 设置心跳距离
- setConnectionTimeout: 设置连贯超时工夫
- setAutomaticReconnect: 设置是否主动重连

如果要应用自签名证书进行 TLS/SSL 连贯，需增加 bcpkix-jdk15on 到 pom.xml 文件。

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

而后应用如下代码创立 SSLUtils.java 文件。

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();}
}

参照如下设置 options。

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

创立一个公布客户端类 PublishSample，该类将公布一条 Hello MQTT 音讯至主题 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());
           // 连贯参数
           MqttConnectOptions options = new MqttConnectOptions();
           // 设置用户名和明码
           options.setUserName(username);
           options.setPassword(password.toCharArray());
           options.setConnectionTimeout(60);
      options.setKeepAliveInterval(60);
           // 连贯
           client.connect(options);
           // 创立音讯并设置 QoS
           MqttMessage message = new MqttMessage(content.getBytes());
           message.setQos(qos);
           // 公布音讯
           client.publish(topic, message);
           System.out.println("Message published");
           System.out.println("topic:" + topic);
           System.out.println("message content:" + content);
           // 敞开连贯
           client.disconnect();
           // 敞开客户端
           client.close();} catch (MqttException e) {throw new RuntimeException(e);
      }
  }
}

创立一个订阅客户端类 SubscribeSample，该类将订阅主题 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());
           // 连贯参数
           MqttConnectOptions options = new MqttConnectOptions();
           options.setUserName(username);
           options.setPassword(password.toCharArray());
           options.setConnectionTimeout(60);
      options.setKeepAliveInterval(60);
           // 设置回调
           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();
      }
  }
}

MqttCallback 阐明：

connectionLost(Throwable cause): 连贯失落时被调用
messageArrived(String topic, MqttMessage message): 接管到音讯时被调用
deliveryComplete(IMqttDeliveryToken token): 音讯发送实现时被调用

接下来运行 SubscribeSample，订阅 mqtt/test 主题。而后运行 PublishSample，公布音讯到 mqtt/test 主题。咱们将会看到公布端胜利公布音讯，同时订阅端接管到音讯。

至此，咱们实现了在 Java 中应用 Paho Java Client 来作为 MQTT 客户端连贯到公共 MQTT 服务器，并实现了测试客户端与 MQTT 服务器的连贯、音讯公布和订阅。

版权申明：本文为 EMQ 原创，转载请注明出处。

原文链接：https://www.emqx.com/zh/blog/how-to-use-mqtt-in-java

关于物联网:如何在-Java-中使用-MQTT

引入客户端库

创立 MQTT 连贯

MQTT 服务器

一般 TCP 连贯

TLS/SSL 连贯

公布 MQTT 音讯

订阅 MQTT 主题

测试