public MqttClientConnection build()

in sdk/src/main/java/software/amazon/awssdk/iot/AwsIotMqttConnectionBuilder.java [489:560]
50 lines of code
12 McCabe index (conditional complexity)

    public MqttClientConnection build() {
        // Validate
        if (bootstrap == null) {
            throw new MqttException("client bootstrap must be non-null");
        }

        // Lazy create
        // This does mean that once you call build() once, modifying the tls context options or client bootstrap
        // has no affect on subsequently-created connections.
        synchronized(this) {
            if (tlsOptions != null && (tlsContext == null || resetLazilyCreatedResources)) {
                try (ClientTlsContext clientTlsContext = new ClientTlsContext(tlsOptions)) {
                    swapReferenceTo(tlsContext, clientTlsContext);
                    tlsContext = clientTlsContext;
                }
            }

            if (client == null || resetLazilyCreatedResources) {
                try (MqttClient mqttClient = (tlsContext == null) ? new MqttClient(bootstrap) : new MqttClient(bootstrap, tlsContext)) {
                    swapReferenceTo(client, mqttClient);
                    client = mqttClient;
                    config.setMqttClient(client);
                }
            }
        }

        resetLazilyCreatedResources = false;

        // Connection create
        try (MqttConnectionConfig connectionConfig = config.clone()) {

            // Whether or not a username has been added, append our metrics tokens
            String usernameOrEmpty = "";
            if (connectionConfig.getUsername() != null) {
                usernameOrEmpty = connectionConfig.getUsername();
            }
            connectionConfig.setUsername(String.format("%s?SDK=JavaV2&Version=%s", usernameOrEmpty, new PackageInfo().version.toString()));

            if (connectionConfig.getUseWebsockets() && connectionConfig.getWebsocketHandshakeTransform() == null) {
                if (websocketCredentialsProvider == null) {
                    DefaultChainCredentialsProvider.DefaultChainCredentialsProviderBuilder providerBuilder = new DefaultChainCredentialsProvider.DefaultChainCredentialsProviderBuilder();
                    providerBuilder.withClientBootstrap(bootstrap);

                    try (CredentialsProvider defaultProvider = providerBuilder.build()) {
                        withWebsocketCredentialsProvider(defaultProvider);
                    }
                }

                try (AwsSigningConfig signingConfig = new AwsSigningConfig()) {
                    signingConfig.setAlgorithm(AwsSigningConfig.AwsSigningAlgorithm.SIGV4);
                    signingConfig.setSignatureType(AwsSigningConfig.AwsSignatureType.HTTP_REQUEST_VIA_QUERY_PARAMS);
                    signingConfig.setRegion(websocketSigningRegion);
                    signingConfig.setService(IOT_SIGNING_SERVICE);
                    signingConfig.setCredentialsProvider(websocketCredentialsProvider);
                    signingConfig.setOmitSessionToken(true);

                    try (AwsSigv4HandshakeTransformer transformer = new AwsSigv4HandshakeTransformer(signingConfig)) {
                        connectionConfig.setWebsocketHandshakeTransform(transformer);

                        /*
                         * transformer is actually a CrtResource since we track a SigningConfig (which tracks a Credentials Provider
                         * But the MqttConnectionConfig only knows of the transformer as a Consumer function, so it's not
                         * able to properly add a forward reference to the transformer.  So we do it manually here after setting.
                         */
                        connectionConfig.addReferenceTo(transformer);
                    }
                }
            }

            return new MqttClientConnection(connectionConfig);
        }
    }