Optimize ArrayList allocations

spring-amqp/src/main/java/org/springframework/amqp/core/AbstractDeclarable.java

@@ -35,6 +35,8 @@
  * @author Gary Russell
  * @author Christian Tzolov
  * @author Ngoc Nhan
+ * @author Artem Bilan
+ *
  * @since 1.2
  *
  */
@@ -104,16 +106,20 @@ public void setIgnoreDeclarationExceptions(boolean ignoreDeclarationExceptions)
 	@Override
 	@SuppressWarnings("NullAway") // Dataflow analysis limitation
 	public void setAdminsThatShouldDeclare(@Nullable Object @Nullable ... adminArgs) {
-		Collection<Object> admins = new ArrayList<>();
 		if (adminArgs != null) {
 			if (adminArgs.length > 1) {
 				Assert.noNullElements(adminArgs, "'admins' cannot contain null elements");
 			}
 			if (adminArgs.length > 0 && !(adminArgs.length == 1 && adminArgs[0] == null)) {
-				admins = Arrays.asList(adminArgs);
+				this.declaringAdmins = Arrays.asList(adminArgs);
+			}
+			else {
+				this.declaringAdmins = Collections.emptyList();
 			}
 		}
-		this.declaringAdmins = admins;
+		else {
+			this.declaringAdmins = Collections.emptyList();
+		}
 	}
 
 	@Override

spring-amqp/src/main/java/org/springframework/amqp/core/Declarables.java

@@ -31,20 +31,27 @@
  *
  * @author Gary Russell
  * @author Björn Michael
+ * @author Artem Bilan
+ *
  * @since 2.1
  */
 public class Declarables {
 
-	private final Collection<Declarable> declarables = new ArrayList<>();
+	private final Collection<Declarable> declarables;
 
 	public Declarables(Declarable... declarables) {
 		if (!ObjectUtils.isEmpty(declarables)) {
+			this.declarables = new ArrayList<>(declarables.length);
 			this.declarables.addAll(Arrays.asList(declarables));
 		}
+		else {
+			this.declarables = new ArrayList<>();
+		}
 	}
 
 	public Declarables(Collection<? extends Declarable> declarables) {
 		Assert.notNull(declarables, "declarables cannot be null");
+		this.declarables = new ArrayList<>(declarables.size());
 		this.declarables.addAll(declarables);
 	}
 

spring-amqp/src/main/java/org/springframework/amqp/support/postprocessor/MessagePostProcessorUtils.java

@@ -38,9 +38,10 @@
 public final class MessagePostProcessorUtils {
 
 	public static Collection<MessagePostProcessor> sort(Collection<MessagePostProcessor> processors) {
-		List<MessagePostProcessor> priorityOrdered = new ArrayList<>();
-		List<MessagePostProcessor> ordered = new ArrayList<>();
-		List<MessagePostProcessor> unOrdered = new ArrayList<>();
+		int potentialSize = processors.size();
+		List<MessagePostProcessor> priorityOrdered = new ArrayList<>(potentialSize);
+		List<MessagePostProcessor> ordered = new ArrayList<>(potentialSize);
+		List<MessagePostProcessor> unOrdered = new ArrayList<>(potentialSize);
 		for (MessagePostProcessor processor : processors) {
 			if (processor instanceof PriorityOrdered) {
 				priorityOrdered.add(processor);

spring-rabbit-stream/src/main/java/org/springframework/rabbit/stream/config/SuperStream.java

@@ -102,9 +102,9 @@ private static Collection<Declarable> declarables(String name, int partitions,
 			BiFunction<String, Integer, List<String>> routingKeyStrategy,
 			Map<String, Object> arguments) {
 
-		List<Declarable> declarables = new ArrayList<>();
 		List<String> rks = routingKeyStrategy.apply(name, partitions);
 		Assert.state(rks.size() == partitions, () -> "Expected " + partitions + " routing keys, not " + rks.size());
+		List<Declarable> declarables = new ArrayList<>(partitions + 1);
 		declarables.add(
 				new DirectExchange(name, true, false, Map.<String, @Nullable Object>of("x-super-stream", true)));
 

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

@@ -361,7 +361,7 @@ else if (source instanceof Method method) {
 	private void processMultiMethodListeners(RabbitListener[] classLevelListeners, Method[] multiMethods,
 			Object bean, String beanName) {
 
-		List<Method> checkedMethods = new ArrayList<>();
+		List<Method> checkedMethods = new ArrayList<>(multiMethods.length);
 		Method defaultMethod = null;
 		for (Method method : multiMethods) {
 			Method checked = checkProxy(method, bean);
@@ -646,8 +646,8 @@ private List<Object> resolveQueues(RabbitListener rabbitListener, Collection<Dec
 		String[] queues = rabbitListener.queues();
 		QueueBinding[] bindings = rabbitListener.bindings();
 		org.springframework.amqp.rabbit.annotation.Queue[] queuesToDeclare = rabbitListener.queuesToDeclare();
-		List<String> queueNames = new ArrayList<>();
-		List<Queue> queueBeans = new ArrayList<>();
+		List<String> queueNames = new ArrayList<>(queues.length);
+		List<Queue> queueBeans = new ArrayList<>(queues.length);
 		for (String queue : queues) {
 			resolveQueues(queue, queueNames, queueBeans);
 		}
@@ -818,7 +818,7 @@ private void registerBindings(QueueBinding binding, String queueName, String exc
 		}
 		else {
 			final int length = binding.key().length;
-			routingKeys = new ArrayList<>();
+			routingKeys = new ArrayList<>(length);
 			for (int i = 0; i < length; ++i) {
 				resolveAsStringOrQueue(resolveExpression(binding.key()[i]), routingKeys, null, "@QueueBinding.key");
 			}

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

@@ -37,11 +37,13 @@
 /**
  * A simple batching strategy that supports only one exchange/routingKey; includes a batch
  * size, a batched message size limit and a timeout. The message properties from the first
- * message in the batch is used in the batch message. Each message is preceded by a 4 byte
+ * message in the batch are used in the batch message. Each message is preceded by a 4-byte
  * length field.
  *
  * @author Gary Russell
  * @author Ngoc Nhan
+ * @author Artem Bilan
+ *
  * @since 1.4.1
  *
  */
@@ -53,7 +55,7 @@ public class SimpleBatchingStrategy implements BatchingStrategy {
 
 	private final long timeout;
 
-	private final List<Message> messages = new ArrayList<>();
+	private final List<Message> messages;
 
 	private @Nullable String exchange;
 
@@ -68,6 +70,7 @@ public class SimpleBatchingStrategy implements BatchingStrategy {
 	 * @param timeout the batch timeout.
 	 */
 	public SimpleBatchingStrategy(int batchSize, int bufferLimit, long timeout) {
+		this.messages = new ArrayList<>(batchSize);
 		this.batchSize = batchSize;
 		this.bufferLimit = bufferLimit;
 		this.timeout = timeout;

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

@@ -30,20 +30,21 @@
  *
  * @author Rene Felgentraeger
  * @author Gary Russell
+ * @author Artem Bilan
  *
  * @since 2.4.8
  */
 public class CompositeContainerCustomizer<C extends MessageListenerContainer> implements ContainerCustomizer<C> {
 
-	private final List<ContainerCustomizer<C>> customizers = new ArrayList<>();
+	private final List<ContainerCustomizer<C>> customizers;
 
 	/**
 	 * Create an instance with the provided delegate customizers.
 	 * @param customizers the customizers.
 	 */
 	public CompositeContainerCustomizer(List<ContainerCustomizer<C>> customizers) {
 		Assert.notNull(customizers, "At least one customizer must be present");
-		this.customizers.addAll(customizers);
+		this.customizers = new ArrayList<>(customizers);
 	}
 
 	@Override

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

@@ -917,7 +917,7 @@ public Collection<PendingConfirm> expire(Listener listener, long cutoffTime) {
 				return Collections.emptyList();
 			}
 
-			List<PendingConfirm> expired = new ArrayList<>();
+			List<PendingConfirm> expired = new ArrayList<>(pendingConfirmsForListener.size());
 			Iterator<Entry<Long, PendingConfirm>> iterator = pendingConfirmsForListener.entrySet().iterator();
 			while (iterator.hasNext()) {
 				PendingConfirm pendingConfirm = iterator.next().getValue();
@@ -926,7 +926,7 @@ public Collection<PendingConfirm> expire(Listener listener, long cutoffTime) {
 					iterator.remove();
 					CorrelationData correlationData = pendingConfirm.getCorrelationData();
 					if (correlationData != null && StringUtils.hasText(correlationData.getId())) {
-						this.pendingReturns.remove(correlationData.getId()); // NOSONAR never null
+						this.pendingReturns.remove(correlationData.getId());
 					}
 				}
 				else {

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/core/RabbitTemplate.java

@@ -679,7 +679,7 @@ public void setBeforePublishPostProcessors(MessagePostProcessor... beforePublish
 	public void addBeforePublishPostProcessors(MessagePostProcessor... beforePublishPostProcessors) {
 		Assert.notNull(beforePublishPostProcessors, "'beforePublishPostProcessors' cannot be null");
 		if (this.beforePublishPostProcessors == null) {
-			this.beforePublishPostProcessors = new ArrayList<>();
+			this.beforePublishPostProcessors = new ArrayList<>(beforePublishPostProcessors.length);
 		}
 		this.beforePublishPostProcessors.addAll(Arrays.asList(beforePublishPostProcessors));
 		this.beforePublishPostProcessors = MessagePostProcessorUtils.sort(this.beforePublishPostProcessors);
@@ -740,7 +740,7 @@ public void setAfterReceivePostProcessors(MessagePostProcessor... afterReceivePo
 	public void addAfterReceivePostProcessors(MessagePostProcessor... afterReceivePostProcessors) {
 		Assert.notNull(afterReceivePostProcessors, "'afterReceivePostProcessors' cannot be null");
 		if (this.afterReceivePostProcessors == null) {
-			this.afterReceivePostProcessors = new ArrayList<>();
+			this.afterReceivePostProcessors = new ArrayList<>(afterReceivePostProcessors.length);
 		}
 		this.afterReceivePostProcessors.addAll(Arrays.asList(afterReceivePostProcessors));
 		this.afterReceivePostProcessors = MessagePostProcessorUtils.sort(this.afterReceivePostProcessors);

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/listener/MultiMethodRabbitListenerEndpoint.java

@@ -71,7 +71,7 @@ public void setValidator(Validator validator) {
 
 	@Override
 	protected HandlerAdapter configureListenerAdapter(MessagingMessageListenerAdapter messageListener) {
-		List<InvocableHandlerMethod> invocableHandlerMethods = new ArrayList<>();
+		List<InvocableHandlerMethod> invocableHandlerMethods = new ArrayList<>(this.methods.size());
 		InvocableHandlerMethod defaultHandler = null;
 		MessageHandlerMethodFactory messageHandlerMethodFactory = getMessageHandlerMethodFactory();
 		Assert.state(messageHandlerMethodFactory != null,

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/listener/adapter/BatchMessagingMessageListenerAdapter.java

@@ -66,7 +66,7 @@ public void onMessageBatch(List<org.springframework.amqp.core.Message> messages,
 			converted = new GenericMessage<>(messages);
 		}
 		else {
-			List<Message<?>> messagingMessages = new ArrayList<>();
+			List<Message<?>> messagingMessages = new ArrayList<>(messages.size());
 			for (org.springframework.amqp.core.Message message : messages) {
 				try {
 					Message<?> messagingMessage = toMessagingMessage(message);
@@ -88,7 +88,7 @@ public void onMessageBatch(List<org.springframework.amqp.core.Message> messages,
 				converted = new GenericMessage<>(messagingMessages);
 			}
 			else {
-				List<Object> payloads = new ArrayList<>();
+				List<Object> payloads = new ArrayList<>(messagingMessages.size());
 				for (Message<?> message : messagingMessages) {
 					payloads.add(message.getPayload());
 				}

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/listener/adapter/MessageListenerAdapter.java

@@ -20,6 +20,7 @@
 import java.lang.reflect.InvocationTargetException;
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import com.rabbitmq.client.Channel;
@@ -116,7 +117,7 @@
  * }
  * </pre>
  *
- * For further examples and discussion please do refer to the Spring reference documentation which describes this class
+ * For further examples and discussion, please do refer to the Spring reference documentation which describes this class
  * (and its attendant XML configuration) in detail.
  *
  * @author Juergen Hoeller
@@ -189,7 +190,7 @@ public MessageListenerAdapter(Object delegate, String defaultListenerMethod) {
 	}
 
 	/**
-	 * Set a target object to delegate message listening to. Specified listener methods have to be present on this
+	 * Set a target object to delegate a message listening to. Specified listener methods have to be present on this
 	 * target object.
 	 * <p> If no explicit delegate object has been specified, listener methods are expected to present on this adapter
 	 * instance, that is, on a custom subclass of this adapter, defining listener methods.
@@ -205,7 +206,7 @@ private void doSetDelegate(Object delegate) {
 	}
 
 	/**
-	 * @return The target object to delegate message listening to.
+	 * @return The target object to delegate a message listening to.
 	 */
 	protected Object getDelegate() {
 		return this.delegate;
@@ -229,8 +230,8 @@ protected String getDefaultListenerMethod() {
 	}
 
 	/**
-	 * Set the mapping of queue name or consumer tag to method name. The first lookup
-	 * is by queue name, if that returns null, we lookup by consumer tag, if that
+	 * Set the mapping of the queue name or consumer tag to the method name. The first lookup
+	 * is by queue name, if that returns null, we look up by consumer tag, if that
 	 * returns null, the {@link #setDefaultListenerMethod(String) defaultListenerMethod}
 	 * is used.
 	 * @param queueOrTagToMethodName the map.
@@ -242,7 +243,7 @@ public void setQueueOrTagToMethodName(Map<String, String> queueOrTagToMethodName
 
 	/**
 	 * Add the mapping of a queue name or consumer tag to a method name. The first lookup
-	 * is by queue name, if that returns null, we lookup by consumer tag, if that
+	 * is by queue name, if that returns null, we look up by consumer tag, if that
 	 * returns null, the {@link #setDefaultListenerMethod(String) defaultListenerMethod}
 	 * is used.
 	 * @param queueOrTag The queue name or consumer tag.
@@ -266,14 +267,14 @@ public String removeQueueOrTagToMethodName(String queueOrTag) {
 	/**
 	 * Spring {@link ChannelAwareMessageListener} entry point.
 	 * <p>
-	 * Delegates the message to the target listener method, with appropriate conversion of the message argument. If the
-	 * target method returns a non-null object, wrap in a Rabbit message and send it back.
+	 * Delegates the message to the target listener method, with the appropriate conversion of the message argument.
+	 * If the target method returns a non-null object, wrap in a Rabbit message and send it back.
 	 * @param message the incoming Rabbit message
 	 * @param channel the Rabbit channel to operate on
 	 * @throws Exception if thrown by Rabbit API methods
 	 */
 	@Override
-	public void onMessage(Message message, @Nullable Channel channel) throws Exception { // NOSONAR
+	public void onMessage(Message message, @Nullable Channel channel) throws Exception {
 		// Check whether the delegate is a MessageListener impl itself.
 		// In that case, the adapter will simply act as a pass-through.
 		Object delegateListener = getDelegate();
@@ -335,12 +336,12 @@ protected String getListenerMethodName(Message originalMessage, Object extracted
 	 * Build an array of arguments to be passed into the target listener method. Allows for multiple method arguments to
 	 * be built from a single message object.
 	 * <p>
-	 * The default implementation builds an array with the given message object as sole element. This means that the
+	 * The default implementation builds an array with the given message object as a sole element. This means that the
 	 * extracted message will always be passed into a <i>single</i> method argument, even if it is an array, with the
 	 * target method having a corresponding single argument of the array's type declared.
 	 * <p>
-	 * This can be overridden to treat special message content such as arrays differently, for example passing in each
-	 * element of the message array as distinct method argument.
+	 * This can be overridden to treat special message content such as arrays differently, for example, passing in each
+	 * element of the message array as a distinct method argument.
 	 * @param extractedMessage the content of the message
 	 * @param channel the Rabbit channel to operate on
 	 * @param message the incoming Rabbit message
@@ -376,16 +377,17 @@ protected Object[] buildListenerArguments(Object extractedMessage, @Nullable Cha
 		catch (InvocationTargetException ex) {
 			Throwable targetEx = ex.getTargetException();
 			if (targetEx instanceof IOException iox) {
-				throw new AmqpIOException(iox); // NOSONAR lost stack trace
+				throw new AmqpIOException(iox);
 			}
 			else {
-				throw new ListenerExecutionFailedException("Listener method '" // NOSONAR lost stack trace
+				throw new ListenerExecutionFailedException("Listener method '"
 						+ methodName + "' threw exception", targetEx, originalMessage);
 			}
 		}
 		catch (Exception ex) {
-			ArrayList<String> arrayClass = new ArrayList<>();
+			List<String> arrayClass = null;
 			if (arguments != null) {
+				arrayClass = new ArrayList<>(arguments.length);
 				for (Object argument : arguments) {
 					arrayClass.add(argument != null ? argument.getClass().toString() : " null");
 				}

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/support/ListenerExecutionFailedException.java

@@ -16,7 +16,6 @@
 
 package org.springframework.amqp.rabbit.support;
 
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
@@ -27,7 +26,6 @@
 import org.springframework.amqp.AmqpException;
 import org.springframework.amqp.core.Message;
 
-
 /**
  * Exception to be thrown when the execution of a listener method failed.
  *
@@ -40,7 +38,7 @@
 @SuppressWarnings("serial")
 public class ListenerExecutionFailedException extends AmqpException {
 
-	private final List<Message> failedMessages = new ArrayList<>();
+	private final List<Message> failedMessages;
 
 	/**
 	 * Constructor for ListenerExecutionFailedException.
@@ -50,7 +48,7 @@ public class ListenerExecutionFailedException extends AmqpException {
 	 */
 	public ListenerExecutionFailedException(String msg, Throwable cause, Message... failedMessage) {
 		super(msg, cause);
-		this.failedMessages.addAll(Arrays.asList(failedMessage));
+		this.failedMessages = Arrays.asList(failedMessage);
 	}
 
 	public @Nullable Message getFailedMessage() {