Checkstyle changes

* Upgrade to Checkstyle 9.0
* apply some JavaDocs rules
* Fix JavaDocs rules violations
* Some other minor clean up in the affected classes

spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/config/xml/MqttMessageDrivenChannelAdapterParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -26,10 +26,11 @@ import org.springframework.integration.config.xml.IntegrationNamespaceUtils;
 import org.springframework.integration.mqtt.inbound.MqttPahoMessageDrivenChannelAdapter;
 
 /**
- * The MqttAdapter Message Driven Channel adapter parser
+ * The MqttAdapter Message Driven Channel adapter parser.
  *
  * @author Gary Russell
  * @author Artem Bilan
+ *
  * @since 4.0
  *
  */

spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/config/xml/MqttNamespaceHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -19,9 +19,10 @@ package org.springframework.integration.mqtt.config.xml;
 import org.springframework.integration.config.xml.AbstractIntegrationNamespaceHandler;
 
 /**
- * The namespace handler for the MqttAdapter namespace
+ * The namespace handler for the MqttAdapter namespace.
  *
  * @author Gary Russell
+ *
  * @since 4.0
  *
  */

spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/outbound/AbstractMqttMessageHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -117,8 +117,8 @@ public abstract class AbstractMqttMessageHandler extends AbstractMessageHandler
 	 * Set the qos expression; default "headers['mqtt_qos']".
 	 * Only applies if a message converter is not provided.
 	 * @param qosExpression the expression.
-	 * @see #setConverter(MessageConverter)
 	 * @since 5.0
+	 * @see #setConverter(MessageConverter)
 	 */
 	public void setQosExpression(Expression qosExpression) {
 		Assert.notNull(qosExpression, "'qosExpression' cannot be null");
@@ -129,8 +129,8 @@ public abstract class AbstractMqttMessageHandler extends AbstractMessageHandler
 	 * Set the qos expression; default "headers['mqtt_qos']".
 	 * Only applies if a message converter is not provided.
 	 * @param qosExpression the expression.
-	 * @see #setConverter(MessageConverter)
 	 * @since 5.0
+	 * @see #setConverter(MessageConverter)
 	 */
 	public void setQosExpressionString(String qosExpression) {
 		Assert.hasText(qosExpression, "'qosExpression' must not be null or empty");
@@ -152,8 +152,8 @@ public abstract class AbstractMqttMessageHandler extends AbstractMessageHandler
 	 * Set the retained expression; default "headers['mqtt_retained']".
 	 * Only applies if a message converter is not provided.
 	 * @param retainedExpression the expression.
-	 * @see #setConverter(MessageConverter)
 	 * @since 5.0
+	 * @see #setConverter(MessageConverter)
 	 */
 	public void setRetainedExpression(Expression retainedExpression) {
 		Assert.notNull(retainedExpression, "'qosExpression' cannot be null");
@@ -164,8 +164,8 @@ public abstract class AbstractMqttMessageHandler extends AbstractMessageHandler
 	 * Set the retained expression; default "headers['mqtt_retained']".
 	 * Only applies if a message converter is not provided.
 	 * @param retainedExpression the expression.
-	 * @see #setConverter(MessageConverter)
 	 * @since 5.0
+	 * @see #setConverter(MessageConverter)
 	 */
 	public void setRetainedExpressionString(String retainedExpression) {
 		Assert.hasText(retainedExpression, "'qosExpression' must not be null or empty");

spring-integration-mqtt/src/main/java/org/springframework/integration/mqtt/support/MqttUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 the original author or authors.
+ * Copyright 2020-2021 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.
@@ -21,9 +21,10 @@ import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
 import org.springframework.beans.BeanUtils;
 
 /**
- * MQTT Utilities
+ * MQTT Utilities.
  *
  * @author Gary Russell
+ *
  * @since 5.4
  *
  */