Improve conditions in code

* Reduce `else` condition and modernize switch pattern
* Check condition after calling lock method
* Some additional code clean up

spring-rabbit-stream/src/main/java/org/springframework/rabbit/stream/producer/RabbitStreamTemplate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2021-2023 the original author or authors.
+ * Copyright 2021-2024 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.
@@ -55,6 +55,7 @@
  *
  * @author Gary Russell
  * @author Christian Tzolov
+ * @author Ngoc Nhan
  * @since 2.4
  *
  */
@@ -107,29 +108,31 @@ public RabbitStreamTemplate(Environment environment, String streamName) {
 
 
 	private Producer createOrGetProducer() {
-		this.lock.lock();
-		try {
-			if (this.producer == null) {
-				ProducerBuilder builder = this.environment.producerBuilder();
-				if (this.superStreamRouting == null) {
-					builder.stream(this.streamName);
-				}
-				else {
-					builder.superStream(this.streamName)
-							.routing(this.superStreamRouting);
-				}
-				this.producerCustomizer.accept(this.beanName, builder);
-				this.producer = builder.build();
-				if (!this.streamConverterSet) {
-					((DefaultStreamMessageConverter) this.streamConverter).setBuilderSupplier(
-							() -> this.producer.messageBuilder());
+		if (this.producer == null) {
+			this.lock.lock();
+			try {
+				if (this.producer == null) {
+					ProducerBuilder builder = this.environment.producerBuilder();
+					if (this.superStreamRouting == null) {
+						builder.stream(this.streamName);
+					}
+					else {
+						builder.superStream(this.streamName)
+								.routing(this.superStreamRouting);
+					}
+					this.producerCustomizer.accept(this.beanName, builder);
+					this.producer = builder.build();
+					if (!this.streamConverterSet) {
+						((DefaultStreamMessageConverter) this.streamConverter).setBuilderSupplier(
+								() -> this.producer.messageBuilder());
+					}
 				}
 			}
-			return this.producer;
-		}
-		finally {
-			this.lock.unlock();
+			finally {
+				this.lock.unlock();
+			}
 		}
+		return this.producer;
 	}
 
 	@Override
@@ -305,24 +308,13 @@ private ConfirmationHandler handleConfirm(CompletableFuture<Boolean> future, Obs
 			}
 			else {
 				int code = confStatus.getCode();
-				String errorMessage;
-				switch (code) {
-				case Constants.CODE_MESSAGE_ENQUEUEING_FAILED:
-					errorMessage = "Message Enqueueing Failed";
-					break;
-				case Constants.CODE_PRODUCER_CLOSED:
-					errorMessage = "Producer Closed";
-					break;
-				case Constants.CODE_PRODUCER_NOT_AVAILABLE:
-					errorMessage = "Producer Not Available";
-					break;
-				case Constants.CODE_PUBLISH_CONFIRM_TIMEOUT:
-					errorMessage = "Publish Confirm Timeout";
-					break;
-				default:
-					errorMessage = "Unknown code: " + code;
-					break;
-				}
+				String errorMessage = switch (code) {
+					case Constants.CODE_MESSAGE_ENQUEUEING_FAILED -> "Message Enqueueing Failed";
+					case Constants.CODE_PRODUCER_CLOSED -> "Producer Closed";
+					case Constants.CODE_PRODUCER_NOT_AVAILABLE -> "Producer Not Available";
+					case Constants.CODE_PUBLISH_CONFIRM_TIMEOUT -> "Publish Confirm Timeout";
+					default -> "Unknown code: " + code;
+				};
 				StreamSendException ex = new StreamSendException(errorMessage, code);
 				observation.error(ex);
 				observation.stop();
@@ -339,15 +331,17 @@ private ConfirmationHandler handleConfirm(CompletableFuture<Boolean> future, Obs
 	 */
 	@Override
 	public void close() {
-		this.lock.lock();
-		try {
-			if (this.producer != null) {
-				this.producer.close();
-				this.producer = null;
+		if (this.producer != null) {
+			this.lock.lock();
+			try {
+				if (this.producer != null) {
+					this.producer.close();
+					this.producer = null;
+				}
+			}
+			finally {
+				this.lock.unlock();
 			}
-		}
-		finally {
-			this.lock.unlock();
 		}
 	}
 

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/annotation/RabbitListenerAnnotationBeanPostProcessor.java

@@ -76,6 +76,7 @@
 import org.springframework.context.expression.StandardBeanExpressionResolver;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.AnnotationUtils;
+import org.springframework.core.annotation.MergedAnnotation;
 import org.springframework.core.annotation.MergedAnnotations;
 import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
 import org.springframework.core.convert.ConversionService;
@@ -357,7 +358,7 @@ else if (source instanceof Method method) {
 					}
 					return !name.contains("$MockitoMock$");
 				})
-				.map(ann -> ann.synthesize())
+				.map(MergedAnnotation::synthesize)
 				.collect(Collectors.toList());
 	}
 
@@ -893,7 +894,7 @@ private void addToMap(Map<String, Object> map, String key, Object value, Class<?
 			}
 		}
 		else {
-			if (value instanceof String && !StringUtils.hasText((String) value)) {
+			if (value instanceof String string && !StringUtils.hasText(string)) {
 				putEmpty(map, key);
 			}
 			else {

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/batch/SimpleBatchingStrategy.java

@@ -107,13 +107,12 @@ public Date nextRelease() {
 		if (this.messages.isEmpty() || this.timeout <= 0) {
 			return null;
 		}
-		else if (this.currentSize >= this.bufferLimit) {
+		if (this.currentSize >= this.bufferLimit) {
 			// release immediately, we're already over the limit
 			return new Date();
 		}
-		else {
-			return new Date(System.currentTimeMillis() + this.timeout);
-		}
+
+		return new Date(System.currentTimeMillis() + this.timeout);
 	}
 
 	@Override
@@ -122,9 +121,8 @@ public Collection<MessageBatch> releaseBatches() {
 		if (batch == null) {
 			return Collections.emptyList();
 		}
-		else {
-			return Collections.singletonList(batch);
-		}
+
+		return Collections.singletonList(batch);
 	}
 
 	private MessageBatch doReleaseBatch() {

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/config/ListenerContainerFactoryBean.java

@@ -575,14 +575,13 @@ private AbstractMessageListenerContainer createContainer() {
 					.acceptIfNotNull(this.retryDeclarationInterval, container::setRetryDeclarationInterval);
 			return container;
 		}
-		else {
-			DirectMessageListenerContainer container = new DirectMessageListenerContainer(this.connectionFactory);
-			JavaUtils.INSTANCE
-					.acceptIfNotNull(this.consumersPerQueue, container::setConsumersPerQueue)
-					.acceptIfNotNull(this.taskScheduler, container::setTaskScheduler)
-					.acceptIfNotNull(this.monitorInterval, container::setMonitorInterval);
-			return container;
-		}
+
+		DirectMessageListenerContainer container = new DirectMessageListenerContainer(this.connectionFactory);
+		JavaUtils.INSTANCE
+				.acceptIfNotNull(this.consumersPerQueue, container::setConsumersPerQueue)
+				.acceptIfNotNull(this.taskScheduler, container::setTaskScheduler)
+				.acceptIfNotNull(this.monitorInterval, container::setMonitorInterval);
+		return container;
 	}
 
 	@Override

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/config/ListenerContainerParser.java

@@ -101,8 +101,8 @@ public BeanDefinition parse(Element element, ParserContext parserContext) {
 		}
 
 		List<Element> childElements = DomUtils.getChildElementsByTagName(element, LISTENER_ELEMENT);
-		for (int i = 0; i < childElements.size(); i++) {
-			parseListener(childElements.get(i), element, parserContext, containerList);
+		for (Element childElement : childElements) {
+			parseListener(childElement, element, parserContext, containerList);
 		}
 
 		parserContext.popAndRegisterContainingComponent();
@@ -190,8 +190,8 @@ private void parseListener(Element listenerEle, Element containerEle, ParserCont
 			else {
 				String[] names = StringUtils.commaDelimitedListToStringArray(queues);
 				List<RuntimeBeanReference> values = new ManagedList<>();
-				for (int i = 0; i < names.length; i++) {
-					values.add(new RuntimeBeanReference(names[i].trim()));
+				for (String name : names) {
+					values.add(new RuntimeBeanReference(name.trim()));
 				}
 				containerDef.getPropertyValues().add("queues", values);
 			}

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/config/StatefulRetryOperationsInterceptorFactoryBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -27,12 +27,14 @@
 import org.springframework.amqp.rabbit.retry.MessageKeyGenerator;
 import org.springframework.amqp.rabbit.retry.MessageRecoverer;
 import org.springframework.amqp.rabbit.retry.NewMessageIdentifier;
+import org.springframework.lang.Nullable;
 import org.springframework.retry.RetryOperations;
 import org.springframework.retry.interceptor.MethodArgumentsKeyGenerator;
 import org.springframework.retry.interceptor.MethodInvocationRecoverer;
 import org.springframework.retry.interceptor.NewMethodArgumentsIdentifier;
 import org.springframework.retry.interceptor.StatefulRetryOperationsInterceptor;
 import org.springframework.retry.support.RetryTemplate;
+import org.springframework.util.Assert;
 
 /**
  * Convenient factory bean for creating a stateful retry interceptor for use in a message listener container, giving you
@@ -47,6 +49,7 @@
  *
  * @author Dave Syer
  * @author Gary Russell
+ * @author Ngoc Nhan
  *
  * @see RetryOperations#execute(org.springframework.retry.RetryCallback, org.springframework.retry.RecoveryCallback,
  * org.springframework.retry.RetryState)
@@ -90,9 +93,8 @@ private NewMethodArgumentsIdentifier createNewItemIdentifier() {
 			if (StatefulRetryOperationsInterceptorFactoryBean.this.newMessageIdentifier == null) {
 				return !message.getMessageProperties().isRedelivered();
 			}
-			else {
-				return StatefulRetryOperationsInterceptorFactoryBean.this.newMessageIdentifier.isNew(message);
-			}
+
+			return StatefulRetryOperationsInterceptorFactoryBean.this.newMessageIdentifier.isNew(message);
 		};
 	}
 
@@ -120,40 +122,33 @@ else if (arg instanceof List && messageRecoverer instanceof MessageBatchRecovere
 	private MethodArgumentsKeyGenerator createKeyGenerator() {
 		return args -> {
 			Message message = argToMessage(args);
+			Assert.notNull(message, "The 'args' must not convert to null");
 			if (StatefulRetryOperationsInterceptorFactoryBean.this.messageKeyGenerator == null) {
 				String messageId = message.getMessageProperties().getMessageId();
 				if (messageId == null && message.getMessageProperties().isRedelivered()) {
 					message.getMessageProperties().setFinalRetryForMessageWithNoId(true);
 				}
 				return messageId;
 			}
-			else {
-				return StatefulRetryOperationsInterceptorFactoryBean.this.messageKeyGenerator.getKey(message);
-			}
+			return StatefulRetryOperationsInterceptorFactoryBean.this.messageKeyGenerator.getKey(message);
 		};
 	}
 
-	@SuppressWarnings("unchecked")
+	@Nullable
 	private Message argToMessage(Object[] args) {
 		Object arg = args[1];
-		Message message = null;
 		if (arg instanceof Message msg) {
-			message = msg;
+			return msg;
 		}
-		else if (arg instanceof List) {
-			message = ((List<Message>) arg).get(0);
+		if (arg instanceof List<?> list) {
+			return (Message) list.get(0);
 		}
-		return message;
+		return null;
 	}
 
 	@Override
 	public Class<?> getObjectType() {
 		return StatefulRetryOperationsInterceptor.class;
 	}
 
-	@Override
-	public boolean isSingleton() {
-		return true;
-	}
-
 }

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/connection/AbstractRoutingConnectionFactory.java

@@ -69,7 +69,7 @@ public void setTargetConnectionFactories(Map<Object, ConnectionFactory> targetCo
 		Assert.noNullElements(targetConnectionFactories.values().toArray(),
 				"'targetConnectionFactories' cannot have null values.");
 		this.targetConnectionFactories.putAll(targetConnectionFactories);
-		targetConnectionFactories.values().stream().forEach(cf -> checkConfirmsAndReturns(cf));
+		targetConnectionFactories.values().forEach(this::checkConfirmsAndReturns);
 	}
 
 	/**
@@ -293,7 +293,7 @@ public void destroy() {
 
 	@Override
 	public void resetConnection() {
-		this.targetConnectionFactories.values().forEach(factory -> factory.resetConnection());
+		this.targetConnectionFactories.values().forEach(ConnectionFactory::resetConnection);
 		this.defaultTargetConnectionFactory.resetConnection();
 	}
 

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/connection/ConsumerChannelRegistry.java

@@ -84,11 +84,9 @@ public static void unRegisterConsumerChannel() {
 	@Nullable
 	public static Channel getConsumerChannel() {
 		ChannelHolder channelHolder = consumerChannel.get();
-		Channel channel = null;
-		if (channelHolder != null) {
-			channel = channelHolder.getChannel();
-		}
-		return channel;
+		return channelHolder != null
+				? channelHolder.getChannel()
+				: null;
 	}
 
 	/**

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/connection/PendingConfirm.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -27,6 +27,7 @@
  * expired. It also holds {@link CorrelationData} for
  * the client to correlate a confirm with a sent message.
  * @author Gary Russell
+ * @author Ngoc Nhan
  * @since 1.0.1
  *
  */
@@ -115,7 +116,7 @@ public void setReturned(boolean isReturned) {
 	 * @since 2.2.10
 	 */
 	public boolean waitForReturnIfNeeded() throws InterruptedException {
-		return this.returned ? this.latch.await(RETURN_CALLBACK_TIMEOUT, TimeUnit.SECONDS) : true;
+		return !this.returned || this.latch.await(RETURN_CALLBACK_TIMEOUT, TimeUnit.SECONDS);
 	}
 
 	/**