sslWithDefaultConfig

HiveMQ Client Library
4

Was able to connect to test.mosquitto.org:8883 by adding the sites certificate to the java cacerts file and running the code below.

found here IBM Docs

KeyStore keyStore = KeyStore.getInstance("JKS");
        // load default jvm keystore
        keyStore.load(new FileInputStream(
                System.getProperties()
                        .getProperty("java.home") + File.separator
                        + "lib" + File.separator + "security" + File.separator
                        + "cacerts"), "changeit".toCharArray());

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

        tmf.init(keyStore);

        Mqtt5BlockingClient client2 = Mqtt5Client.builder()
                .identifier(UUID.randomUUID().toString())
                .serverHost("test.mosquitto.org")
                .serverPort(8883)
                .sslConfig()
                    .trustManagerFactory(tmf)
                    .applySslConfig()
                .buildBlocking();

        client2.connect();