MQTT connect using Java

If you're working on a web or Android application in Java and need to integrate with ClearBlade, this guide provides the necessary details to help you get started.

Maven Dependencies

To connect your Java application to ClearBlade, add the following dependencies to your pom.xml file:

<dependency>
    <groupId>org.eclipse.paho</groupId>
    <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
    <version>1.2.5</version>
</dependency>
<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcprov-jdk15on</artifactId>
    <version>1.70</version>
</dependency>
<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt</artifactId>
    <version>0.9.1</version>
</dependency>

Sample Code

Below is a sample code snippet demonstrating how to integrate ClearBlade into your Java project:

public class MqttConnection {
    public static void main(String[] args) throws Exception {
        String projectId = "";
        String cloudRegion = "";
        String registryId = "";
        String deviceId = "";
        String privateKeyFile = "";
        String caCerts = "";
        String mqttBridgeHostname = "";
        int mqttBridgePort = 8883;
        String clientId = String.format("projects/%s/locations/%s/registries/%s/devices/%s",
            projectId, cloudRegion, registryId, deviceId);

        MqttClient client = new MqttClient("ssl://" + mqttBridgeHostname + ":" + mqttBridgePort, clientId);

        MqttConnectOptions options = new MqttConnectOptions();
        options.setMqttVersion(MqttConnectOptions.MQTT_VERSION_3_1_1);
        options.setSocketFactory(getSocketFactory(caCerts));
        options.setUserName("unused");
        PrivateKey privateKey = getPrivateKeyFromFile(privateKeyFile);
        String jwtToken = generateJwtToken(privateKey, projectId);
        options.setPassword(jwtToken.toCharArray());


        client.setCallback(new MqttCallback() {
            public void connectionLost(Throwable cause) {
                System.out.println("Connection lost");
            }

            public void messageArrived(String topic, MqttMessage message) throws Exception {
                System.out.println("Received message '" + new String(message.getPayload()) +
                    "' on topic '" + topic + "' with QoS " + message.getQos());
            }

            public void deliveryComplete(IMqttDeliveryToken token) {
                System.out.println("Delivery complete");
            }
        });

        client.connect(options);
        System.out.println("Connection successful");

        String mqttConfigTopic = "/devices/" + deviceId + "/config";
        client.subscribe(mqttConfigTopic, 1);
        String mqttCommandTopic = "/devices/" + deviceId + "/commands/#";
        client.subscribe(mqttCommandTopic, 0);
    }

    public static javax.net.ssl.SSLSocketFactory getSocketFactory(String caCerts) {
        try {
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            FileInputStream fis = new FileInputStream(caCerts);
            java.security.cert.X509Certificate caCert = (java.security.cert.X509Certificate) cf.generateCertificate(fis);

            KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
            ks.load(null, null);
            ks.setCertificateEntry("caCert", caCert);

            TrustManagerFactory tmf = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
            tmf.init(ks);

            SSLContext ctx = SSLContext.getInstance("TLS");
            ctx.init(null, tmf.getTrustManagers(), null);

            return ctx.getSocketFactory();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

    private static PrivateKey getPrivateKeyFromFile(String privateKeyFilePath) throws Exception {
        File file = new File(privateKeyFilePath);
        PemObject pemObject;

        try (PemReader pemReader = new PemReader(new FileReader(file))) {
            pemObject = pemReader.readPemObject();
        }

        byte[] content = pemObject.getContent();
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(content);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        return keyFactory.generatePrivate(keySpec);
    }

    private static String generateJwtToken(PrivateKey privateKey, String projectID) {
        return Jwts.builder()
            .claim("iat", System.currentTimeMillis() / 1000)
            .claim("exp", (System.currentTimeMillis() / 1000) + 1440 * 60)
            .claim("aud", projectID)
            .signWith(SignatureAlgorithm.RS256, privateKey)
            .compact();
    }
}