Backport further refinements from the nullability efforts

Issue: SPR-15656

spring-jms/src/main/java/org/springframework/jms/config/AbstractListenerContainerParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -151,15 +151,14 @@ abstract class AbstractListenerContainerParser implements BeanDefinitionParser {
 			listenerDef.getPropertyValues().add("delegate", new RuntimeBeanReference(ref));
 		}
 
-		String method = null;
 		if (listenerEle.hasAttribute(METHOD_ATTRIBUTE)) {
-			method = listenerEle.getAttribute(METHOD_ATTRIBUTE);
+			String method = listenerEle.getAttribute(METHOD_ATTRIBUTE);
 			if (!StringUtils.hasText(method)) {
 				parserContext.getReaderContext().error(
 						"Listener 'method' attribute contains empty value.", listenerEle);
 			}
+			listenerDef.getPropertyValues().add("defaultListenerMethod", method);
 		}
-		listenerDef.getPropertyValues().add("defaultListenerMethod", method);
 
 		PropertyValue messageConverterPv = commonContainerProperties.getPropertyValue("messageConverter");
 		if (messageConverterPv != null) {

spring-jms/src/main/java/org/springframework/jms/connection/JmsResourceHolder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -170,10 +170,7 @@ public class JmsResourceHolder extends ResourceHolderSupport {
 	}
 
 	public Session getSession(Class<? extends Session> sessionType, Connection connection) {
-		List<Session> sessions = this.sessions;
-		if (connection != null) {
-			sessions = this.sessionsPerConnection.get(connection);
-		}
+		List<Session> sessions = (connection != null ? this.sessionsPerConnection.get(connection) : this.sessions);
 		return CollectionUtils.findValueOfType(sessions, sessionType);
 	}
 

spring-jms/src/main/java/org/springframework/jms/connection/JmsTransactionManager.java

@@ -170,7 +170,7 @@ public class JmsTransactionManager extends AbstractPlatformTransactionManager
 	@Override
 	protected boolean isExistingTransaction(Object transaction) {
 		JmsTransactionObject txObject = (JmsTransactionObject) transaction;
-		return (txObject.getResourceHolder() != null);
+		return txObject.hasResourceHolder();
 	}
 
 	@Override
@@ -316,6 +316,10 @@ public class JmsTransactionManager extends AbstractPlatformTransactionManager
 			return this.resourceHolder;
 		}
 
+		public boolean hasResourceHolder() {
+			return (this.resourceHolder != null);
+		}
+
 		@Override
 		public boolean isRollbackOnly() {
 			return this.resourceHolder.isRollbackOnly();

spring-jms/src/main/java/org/springframework/jms/listener/AbstractMessageListenerContainer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -197,7 +197,6 @@ public abstract class AbstractMessageListenerContainer extends AbstractJmsListen
 	 * @see #setDestinationName(String)
 	 */
 	public void setDestination(Destination destination) {
-		Assert.notNull(destination, "'destination' must not be null");
 		this.destination = destination;
 		if (destination instanceof Topic && !(destination instanceof Queue)) {
 			// Clearly a Topic: let's set the "pubSubDomain" flag accordingly.
@@ -223,11 +222,9 @@ public abstract class AbstractMessageListenerContainer extends AbstractJmsListen
 	 * container picking up the new destination immediately (works e.g. with
 	 * DefaultMessageListenerContainer, as long as the cache level is less than
 	 * CACHE_CONSUMER). However, this is considered advanced usage; use it with care!
-	 * @param destinationName the desired destination (can be {@code null})
 	 * @see #setDestination(javax.jms.Destination)
 	 */
 	public void setDestinationName(String destinationName) {
-		Assert.notNull(destinationName, "'destinationName' must not be null");
 		this.destination = destinationName;
 	}
 
@@ -246,7 +243,8 @@ public abstract class AbstractMessageListenerContainer extends AbstractJmsListen
 	 * (never {@code null}).
 	 */
 	protected String getDestinationDescription() {
-		return this.destination.toString();
+		Object destination = this.destination;
+		return (destination != null ? destination.toString() : "");
 	}
 
 	/**
@@ -432,7 +430,7 @@ public abstract class AbstractMessageListenerContainer extends AbstractJmsListen
 	 */
 	public void setDurableSubscriptionName(String durableSubscriptionName) {
 		this.subscriptionName = durableSubscriptionName;
-		this.subscriptionDurable = true;
+		this.subscriptionDurable = (durableSubscriptionName != null);
 	}
 
 	/**

spring-jms/src/main/java/org/springframework/jms/listener/adapter/AbstractAdaptableMessageListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -191,6 +191,9 @@ public abstract class AbstractAdaptableMessageListener
 		}
 	}
 
+	@Override
+	public abstract void onMessage(Message message, Session session) throws JMSException;
+
 	/**
 	 * Handle the given exception that arose during listener execution.
 	 * The default implementation logs the exception at error level.
@@ -204,6 +207,7 @@ public abstract class AbstractAdaptableMessageListener
 		logger.error("Listener execution failed", ex);
 	}
 
+
 	/**
 	 * Extract the message body from the given JMS message.
 	 * @param message the JMS {@code Message}
@@ -453,6 +457,7 @@ public abstract class AbstractAdaptableMessageListener
 		@Override
 		protected Message createMessageForPayload(Object payload, Session session, Object conversionHint)
 				throws JMSException {
+
 			MessageConverter converter = getMessageConverter();
 			if (converter == null) {
 				throw new IllegalStateException("No message converter, cannot handle '" + payload + "'");
@@ -464,6 +469,7 @@ public abstract class AbstractAdaptableMessageListener
 			return converter.toMessage(payload, session);
 		}
 
+
 		protected class LazyResolutionMessage implements org.springframework.messaging.Message<Object> {
 
 			private final javax.jms.Message message;
@@ -487,7 +493,6 @@ public abstract class AbstractAdaptableMessageListener
 								"Failed to extract payload from [" + this.message + "]", ex);
 					}
 				}
-				//
 				return this.payload;
 			}
 
@@ -513,7 +518,6 @@ public abstract class AbstractAdaptableMessageListener
 				return this.headers;
 			}
 		}
-
 	}
 
 

spring-jms/src/main/java/org/springframework/jms/listener/endpoint/StandardJmsActivationSpecFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -94,7 +94,7 @@ public class StandardJmsActivationSpecFactory implements JmsActivationSpecFactor
 	 * Return the {@link DestinationResolver} to use for resolving destinations names.
 	 */
 	public DestinationResolver getDestinationResolver() {
-		return destinationResolver;
+		return this.destinationResolver;
 	}
 
 	@Override