spring-projectsGH-3732 make mqttClient initialize lazily

Author: Mikhail Polivakha

Diff for: spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/inbound/AbstractMqttMessageDrivenChannelAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package org.springframework.integration.mqtt.inbound;
 
 import java.util.LinkedHashSet;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
@@ -140,7 +141,7 @@ protected MqttMessageConverter getConverter() {
 	}
 
 	@ManagedAttribute
-	public String[] getTopic() {
+	public String[] getTopicNames() {
 		this.topicLock.lock();
 		try {
 			String[] topicNames = new String[this.topics.size()];
@@ -331,15 +332,7 @@ public boolean equals(Object obj) {
 				return false;
 			}
 			Topic other = (Topic) obj;
-			if (this.topic == null) {
-				if (other.topic != null) {
-					return false;
-				}
-			}
-			else if (!this.topic.equals(other.topic)) {
-				return false;
-			}
-			return true;
+			return Objects.equals(this.topic, other.topic);
 		}
 
 		@Override

Diff for: spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/inbound/MqttPahoMessageDrivenChannelAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -193,7 +193,7 @@ protected synchronized void doStop() {
 						|| (this.consumerStopAction.equals(ConsumerStopAction.UNSUBSCRIBE_CLEAN)
 						&& this.cleanSession)) {
 
-					this.client.unsubscribe(getTopic());
+					this.client.unsubscribe(getTopicNames());
 				}
 			}
 			catch (MqttException ex) {
@@ -270,7 +270,7 @@ private synchronized void connectAndSubscribe() throws MqttException { // NOSONA
 		}
 
 		this.topicLock.lock();
-		String[] topics = getTopic();
+		String[] topics = getTopicNames();
 		ApplicationEventPublisher applicationEventPublisher = getApplicationEventPublisher();
 		try {
 			this.client.connect(connectionOptions);

Diff for: spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/inbound/Mqttv5PahoMessageDrivenChannelAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2021 the original author or authors.
+ * Copyright 2021-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -141,26 +141,29 @@ public void setHeaderMapper(HeaderMapper<MqttProperties> headerMapper) {
 	@Override
 	protected void onInit() {
 		super.onInit();
+		initializeMqttAsyncClientIfRequired();
+		if (this.messageConverter == null) {
+			setMessageConverter(getBeanFactory()
+					.getBean(IntegrationContextUtils.ARGUMENT_RESOLVER_MESSAGE_CONVERTER_BEAN_NAME,
+							SmartMessageConverter.class));
+		}
+	}
+
+	private void initializeMqttAsyncClient() {
 		try {
 			this.mqttClient = new MqttAsyncClient(getUrl(), getClientId(), this.persistence);
 			this.mqttClient.setCallback(this);
 			this.mqttClient.setManualAcks(isManualAcks());
-		}
-		catch (MqttException ex) {
+		} catch (MqttException ex) {
 			throw new BeanCreationException("Cannot create 'MqttAsyncClient' for: " + getComponentName(), ex);
 		}
-		if (this.messageConverter == null) {
-			setMessageConverter(getBeanFactory()
-					.getBean(IntegrationContextUtils.ARGUMENT_RESOLVER_MESSAGE_CONVERTER_BEAN_NAME,
-							SmartMessageConverter.class));
-		}
 	}
 
 	@Override
 	protected void doStart() {
 		ApplicationEventPublisher applicationEventPublisher = getApplicationEventPublisher();
 		this.topicLock.lock();
-		String[] topics = getTopic();
+		String[] topics = getTopicNames();
 		try {
 			this.mqttClient.connect(this.connectionOptions).waitForCompletion(getCompletionTimeout());
 			if (topics.length > 0) {
@@ -187,33 +190,40 @@ protected void doStart() {
 	@Override
 	protected void doStop() {
 		this.topicLock.lock();
-		String[] topics = getTopic();
+		initializeMqttAsyncClientIfRequired();
+		String[] topics = getTopicNames();
 		try {
 			this.mqttClient.unsubscribe(topics).waitForCompletion(getCompletionTimeout());
 			this.mqttClient.disconnect().waitForCompletion(getCompletionTimeout());
-		}
-		catch (MqttException ex) {
+		} catch (MqttException ex) {
 			logger.error(ex, () -> "Error unsubscribing from " + Arrays.toString(topics));
-		}
-		finally {
+		} finally {
 			this.topicLock.unlock();
 		}
 	}
 
+	private void initializeMqttAsyncClientIfRequired() {
+		if (mqttClient == null) {
+			initializeMqttAsyncClient();
+		}
+	}
+
 	@Override
 	public void destroy() {
 		super.destroy();
 		try {
-			this.mqttClient.close(true);
-		}
-		catch (MqttException ex) {
+			if (mqttClient != null) {
+				this.mqttClient.close(true);
+			}
+		} catch (MqttException ex) {
 			logger.error(ex, "Failed to close 'MqttAsyncClient'");
 		}
 	}
 
 	@Override
 	public void addTopic(String topic, int qos) {
 		this.topicLock.lock();
+		initializeMqttAsyncClientIfRequired();
 		try {
 			this.mqttClient.subscribe(topic, qos).waitForCompletion(getCompletionTimeout());
 			super.addTopic(topic, qos);
@@ -229,6 +239,7 @@ public void addTopic(String topic, int qos) {
 	@Override
 	public void removeTopic(String... topic) {
 		this.topicLock.lock();
+		initializeMqttAsyncClient();
 		try {
 			this.mqttClient.unsubscribe(topic).waitForCompletion(getCompletionTimeout());
 			super.removeTopic(topic);