Optimize new ArrayList() allocations whenever possible

spring-integration-amqp/src/main/java/org/springframework/integration/amqp/inbound/AmqpInboundChannelAdapter.java

@@ -491,7 +491,7 @@ public void onMessageBatch(List<Message> messages, @Nullable Channel channel) {
 			else {
 				converted = convertPayloads(messages, channel);
 				if (BatchMode.EXTRACT_PAYLOADS_WITH_HEADERS.equals(AmqpInboundChannelAdapter.this.batchMode)) {
-					List<Map<String, @Nullable Object>> listHeaders = new ArrayList<>();
+					List<Map<String, @Nullable Object>> listHeaders = new ArrayList<>(messages.size());
 					messages.forEach(msg -> listHeaders.add(AmqpInboundChannelAdapter.this.headerMapper
 							.toHeadersFromRequest(msg.getMessageProperties())));
 					headers = listHeaders;
@@ -553,7 +553,7 @@ public void onMessageBatch(List<Message> messages, @Nullable Channel channel) {
 		private @Nullable List<org.springframework.messaging.Message<?>> convertMessages(List<Message> messages,
 				@Nullable Channel channel) {
 
-			List<org.springframework.messaging.Message<?>> converted = new ArrayList<>();
+			List<org.springframework.messaging.Message<?>> converted = new ArrayList<>(messages.size());
 			try {
 				messages.forEach(message -> converted.add(createMessageFromAmqp(message, channel)));
 				return converted;
@@ -574,7 +574,7 @@ public void onMessageBatch(List<Message> messages, @Nullable Channel channel) {
 		}
 
 		private @Nullable List<?> convertPayloads(List<Message> messages, @Nullable Channel channel) {
-			List<Object> converted = new ArrayList<>();
+			List<Object> converted = new ArrayList<>(messages.size());
 			try {
 				messages.forEach(message -> converted.add(this.converter.fromMessage(message)));
 				return converted;

spring-integration-amqp/src/main/java/org/springframework/integration/amqp/support/DefaultAmqpHeaderMapper.java

@@ -16,7 +16,6 @@
 
 package org.springframework.integration.amqp.support;
 
-import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.List;
@@ -62,36 +61,33 @@
  */
 public class DefaultAmqpHeaderMapper extends AbstractHeaderMapper<MessageProperties> implements AmqpHeaderMapper {
 
-	private static final List<String> STANDARD_HEADER_NAMES = new ArrayList<>();
-
-	static {
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.APP_ID);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.CLUSTER_ID);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.CONTENT_ENCODING);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.CONTENT_LENGTH);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.CONTENT_TYPE);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.CORRELATION_ID);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.DELAY);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.DELIVERY_MODE);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.DELIVERY_TAG);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.EXPIRATION);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.MESSAGE_COUNT);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.MESSAGE_ID);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.RECEIVED_DELAY);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.RECEIVED_DELIVERY_MODE);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.RECEIVED_EXCHANGE);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.RECEIVED_ROUTING_KEY);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.REDELIVERED);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.REPLY_TO);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.TIMESTAMP);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.TYPE);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.USER_ID);
-		STANDARD_HEADER_NAMES.add(JsonHeaders.TYPE_ID);
-		STANDARD_HEADER_NAMES.add(JsonHeaders.CONTENT_TYPE_ID);
-		STANDARD_HEADER_NAMES.add(JsonHeaders.KEY_TYPE_ID);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.SPRING_REPLY_CORRELATION);
-		STANDARD_HEADER_NAMES.add(AmqpHeaders.SPRING_REPLY_TO_STACK);
-	}
+	private static final List<String> STANDARD_HEADER_NAMES =
+			List.of(AmqpHeaders.APP_ID,
+					AmqpHeaders.CLUSTER_ID,
+					AmqpHeaders.CONTENT_ENCODING,
+					AmqpHeaders.CONTENT_LENGTH,
+					AmqpHeaders.CONTENT_TYPE,
+					AmqpHeaders.CORRELATION_ID,
+					AmqpHeaders.DELAY,
+					AmqpHeaders.DELIVERY_MODE,
+					AmqpHeaders.DELIVERY_TAG,
+					AmqpHeaders.EXPIRATION,
+					AmqpHeaders.MESSAGE_COUNT,
+					AmqpHeaders.MESSAGE_ID,
+					AmqpHeaders.RECEIVED_DELAY,
+					AmqpHeaders.RECEIVED_DELIVERY_MODE,
+					AmqpHeaders.RECEIVED_EXCHANGE,
+					AmqpHeaders.RECEIVED_ROUTING_KEY,
+					AmqpHeaders.REDELIVERED,
+					AmqpHeaders.REPLY_TO,
+					AmqpHeaders.TIMESTAMP,
+					AmqpHeaders.TYPE,
+					AmqpHeaders.USER_ID,
+					JsonHeaders.TYPE_ID,
+					JsonHeaders.CONTENT_TYPE_ID,
+					JsonHeaders.KEY_TYPE_ID,
+					AmqpHeaders.SPRING_REPLY_CORRELATION,
+					AmqpHeaders.SPRING_REPLY_TO_STACK);
 
 	@SuppressWarnings("this-escape")
 	protected DefaultAmqpHeaderMapper(String @Nullable [] requestHeaderNames, String @Nullable [] replyHeaderNames) {

spring-integration-core/src/main/java/org/springframework/integration/aggregator/ResequencingMessageGroupProcessor.java

@@ -49,7 +49,7 @@ public Object processMessageGroup(MessageGroup group) {
 		if (!messages.isEmpty()) {
 			List<Message<?>> sorted = new ArrayList<>(messages);
 			sorted.sort(this.comparator);
-			ArrayList<Message<?>> partialSequence = new ArrayList<>();
+			ArrayList<Message<?>> partialSequence = new ArrayList<>(messages.size());
 			int previousSequence = extractSequenceNumber(sorted.get(0));
 			int currentSequence = previousSequence;
 			for (Message<?> message : sorted) {

spring-integration-core/src/main/java/org/springframework/integration/channel/QueueChannel.java

@@ -207,8 +207,8 @@ public List<Message<?>> purge(@Nullable MessageSelector selector) {
 		if (selector == null) {
 			return this.clear();
 		}
-		List<Message<?>> purgedMessages = new ArrayList<>();
 		Object[] array = this.queue.toArray();
+		List<Message<?>> purgedMessages = new ArrayList<>(array.length);
 		for (Object o : array) {
 			Message<?> message = (Message<?>) o;
 			if (!selector.accept(message) && this.queue.remove(message)) {

spring-integration-core/src/main/java/org/springframework/integration/codec/kryo/CompositeKryoRegistrar.java

@@ -29,14 +29,16 @@
  * A {@link KryoRegistrar} that delegates and validates registrations across all components.
  *
  * @author David Turanski
+ * @author Artem Bilan
+ *
  * @since 4.2
  */
 public class CompositeKryoRegistrar extends AbstractKryoRegistrar {
 
 	private final List<KryoRegistrar> delegates;
 
 	public CompositeKryoRegistrar(List<KryoRegistrar> delegates) {
-		this.delegates = new ArrayList<KryoRegistrar>(delegates);
+		this.delegates = new ArrayList<>(delegates);
 
 		if (!CollectionUtils.isEmpty(this.delegates)) {
 			validateRegistrations();
@@ -52,18 +54,19 @@ public void registerTypes(Kryo kryo) {
 
 	@Override
 	public final List<Registration> getRegistrations() {
-		List<Registration> registrations = new ArrayList<Registration>();
+		List<Registration> registrations = new ArrayList<>();
 		for (KryoRegistrar registrar : this.delegates) {
 			registrations.addAll(registrar.getRegistrations());
 		}
 		return registrations;
 	}
 
 	private void validateRegistrations() {
-		List<Integer> ids = new ArrayList<Integer>();
-		List<Class<?>> types = new ArrayList<Class<?>>();
+		List<Registration> registrations = getRegistrations();
+		List<Integer> ids = new ArrayList<>(registrations.size());
+		List<Class<?>> types = new ArrayList<>(registrations.size());
 
-		for (Registration registration : getRegistrations()) {
+		for (Registration registration : registrations) {
 			Assert.isTrue(registration.getId() >= MIN_REGISTRATION_VALUE,
 					"registration ID must be >= " + MIN_REGISTRATION_VALUE);
 			if (ids.contains(registration.getId())) {

spring-integration-core/src/main/java/org/springframework/integration/codec/kryo/KryoClassListRegistrar.java

@@ -64,17 +64,18 @@ public KryoClassListRegistrar(List<Class<?>> classes) {
 	 * @param initialValue the initial value
 	 */
 	public void setInitialValue(int initialValue) {
-		Assert.isTrue(initialValue >= MIN_REGISTRATION_VALUE, "'initialValue' must be >= " + MIN_REGISTRATION_VALUE);
+		Assert.isTrue(initialValue >= MIN_REGISTRATION_VALUE,
+				() -> "'initialValue' must be >= " + MIN_REGISTRATION_VALUE);
 		this.initialValue = initialValue;
 	}
 
 	@Override
 	public List<Registration> getRegistrations() {
-		List<Registration> registrations = new ArrayList<>();
+		List<Registration> registrations = new ArrayList<>(this.registeredClasses.size());
 		if (!CollectionUtils.isEmpty(this.registeredClasses)) {
 			for (int i = 0; i < this.registeredClasses.size(); i++) {
-				registrations.add(new Registration(this.registeredClasses.get(i),
-						KRYO.getSerializer(this.registeredClasses.get(i)), i + this.initialValue));
+				Class<?> type = this.registeredClasses.get(i);
+				registrations.add(new Registration(type, KRYO.getSerializer(type), i + this.initialValue));
 			}
 		}
 		return registrations;

spring-integration-core/src/main/java/org/springframework/integration/codec/kryo/KryoClassMapRegistrar.java

@@ -30,23 +30,25 @@
  * used to explicitly set the registration ID for each class.
  *
  * @author David Turanski
+ * @author Artem Bilan
+ *
  * @since 4.2
  */
 public class KryoClassMapRegistrar extends AbstractKryoRegistrar {
 
 	private final Map<Integer, Class<?>> registeredClasses;
 
 	public KryoClassMapRegistrar(Map<Integer, Class<?>> kryoRegisteredClasses) {
-		this.registeredClasses = new HashMap<Integer, Class<?>>(kryoRegisteredClasses);
+		this.registeredClasses = new HashMap<>(kryoRegisteredClasses);
 	}
 
 	@Override
 	public List<Registration> getRegistrations() {
-		List<Registration> registrations = new ArrayList<Registration>();
+		List<Registration> registrations = new ArrayList<>(this.registeredClasses.size());
 		if (!CollectionUtils.isEmpty(this.registeredClasses)) {
 			for (Map.Entry<Integer, Class<?>> entry : this.registeredClasses.entrySet()) {
-				registrations.add(
-						new Registration(entry.getValue(), KRYO.getSerializer(entry.getValue()), entry.getKey()));
+				Class<?> type = entry.getValue();
+				registrations.add(new Registration(type, KRYO.getSerializer(type), entry.getKey()));
 			}
 		}
 		return registrations;

spring-integration-core/src/main/java/org/springframework/integration/codec/kryo/KryoRegistrationRegistrar.java

@@ -25,16 +25,16 @@
  * A {@link KryoRegistrar} implementation backed by a List of {@link Registration}.
  *
  * @author David Turanski
+ * @author Artem Bilan
+ *
  * @since 4.2
  */
 public class KryoRegistrationRegistrar extends AbstractKryoRegistrar {
 
 	private final List<Registration> registrations;
 
 	public KryoRegistrationRegistrar(List<Registration> registrations) {
-		this.registrations = registrations != null
-				? new ArrayList<Registration>(registrations)
-				: new ArrayList<Registration>();
+		this.registrations = new ArrayList<>(registrations);
 	}
 
 	@Override

spring-integration-core/src/main/java/org/springframework/integration/config/GlobalChannelInterceptorProcessor.java

@@ -120,7 +120,7 @@ public void addMatchingInterceptors(InterceptableChannel channel, String beanNam
 			LOGGER.debug("Applying global interceptors on channel '" + beanName + "'");
 		}
 
-		List<GlobalChannelInterceptorWrapper> tempInterceptors = new ArrayList<>();
+		List<GlobalChannelInterceptorWrapper> tempInterceptors = new ArrayList<>(this.positiveOrderInterceptors.size());
 
 		this.positiveOrderInterceptors
 				.forEach(interceptorWrapper ->

spring-integration-core/src/main/java/org/springframework/integration/config/IntegrationComponentScanRegistrar.java

@@ -76,18 +76,14 @@ public class IntegrationComponentScanRegistrar implements ImportBeanDefinitionRe
 
 	private static final String BEAN_NAME = IntegrationComponentScanRegistrar.class.getName();
 
-	private final List<TypeFilter> defaultFilters = new ArrayList<>();
+	private final List<TypeFilter> defaultFilters = List.of(new AnnotationTypeFilter(MessagingGateway.class, true));
 
 	@SuppressWarnings("NullAway.Init")
 	private ResourceLoader resourceLoader;
 
 	@SuppressWarnings("NullAway.Init")
 	private Environment environment;
 
-	public IntegrationComponentScanRegistrar() {
-		this.defaultFilters.add(new AnnotationTypeFilter(MessagingGateway.class, true));
-	}
-
 	@Override
 	public void setResourceLoader(ResourceLoader resourceLoader) {
 		this.resourceLoader = resourceLoader;
@@ -132,7 +128,7 @@ protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
 
 		};
 
-		filter(registry, componentScan, scanner); // NOSONAR - never null
+		filter(registry, componentScan, scanner);
 
 		scanner.setResourceLoader(this.resourceLoader);
 		scanner.setEnvironment(this.environment);
@@ -151,7 +147,7 @@ protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
 	private void filter(BeanDefinitionRegistry registry, AnnotationAttributes componentScan,
 			ClassPathScanningCandidateComponentProvider scanner) {
 
-		if (componentScan.getBoolean("useDefaultFilters")) { // NOSONAR - never null
+		if (componentScan.getBoolean("useDefaultFilters")) {
 			for (TypeFilter typeFilter : this.defaultFilters) {
 				scanner.addIncludeFilter(typeFilter);
 			}
@@ -188,10 +184,11 @@ protected Collection<String> getBasePackages(AnnotationAttributes componentScan,
 	}
 
 	private List<TypeFilter> typeFiltersFor(AnnotationAttributes filter, BeanDefinitionRegistry registry) {
-		List<TypeFilter> typeFilters = new ArrayList<>();
+		Class<?>[] classes = filter.getClassArray("classes");
+		List<TypeFilter> typeFilters = new ArrayList<>(classes.length);
 		FilterType filterType = filter.getEnum("type");
 
-		for (Class<?> filterClass : filter.getClassArray("classes")) {
+		for (Class<?> filterClass : classes) {
 			switch (filterType) {
 				case ANNOTATION -> {
 					Assert.isAssignable(Annotation.class, filterClass,
@@ -230,23 +227,23 @@ private static void invokeAwareMethods(Object parserStrategyBean, Environment en
 			ResourceLoader resourceLoader, BeanDefinitionRegistry registry) {
 
 		if (parserStrategyBean instanceof Aware) {
-			if (parserStrategyBean instanceof BeanClassLoaderAware) {
+			if (parserStrategyBean instanceof BeanClassLoaderAware beanClassLoaderAware) {
 				ClassLoader classLoader =
 						registry instanceof ConfigurableBeanFactory
 								? ((ConfigurableBeanFactory) registry).getBeanClassLoader()
 								: resourceLoader.getClassLoader();
 				if (classLoader != null) {
-					((BeanClassLoaderAware) parserStrategyBean).setBeanClassLoader(classLoader);
+					beanClassLoaderAware.setBeanClassLoader(classLoader);
 				}
 			}
-			if (parserStrategyBean instanceof BeanFactoryAware && registry instanceof BeanFactory) {
-				((BeanFactoryAware) parserStrategyBean).setBeanFactory((BeanFactory) registry);
+			if (parserStrategyBean instanceof BeanFactoryAware beanFactoryAware && registry instanceof BeanFactory) {
+				beanFactoryAware.setBeanFactory((BeanFactory) registry);
 			}
-			if (parserStrategyBean instanceof EnvironmentAware) {
-				((EnvironmentAware) parserStrategyBean).setEnvironment(environment);
+			if (parserStrategyBean instanceof EnvironmentAware environmentAware) {
+				environmentAware.setEnvironment(environment);
 			}
-			if (parserStrategyBean instanceof ResourceLoaderAware) {
-				((ResourceLoaderAware) parserStrategyBean).setResourceLoader(resourceLoader);
+			if (parserStrategyBean instanceof ResourceLoaderAware resourceLoaderAware) {
+				resourceLoaderAware.setResourceLoader(resourceLoader);
 			}
 		}
 	}

spring-integration-core/src/main/java/org/springframework/integration/config/MessagingAnnotationBeanPostProcessor.java

@@ -63,7 +63,7 @@ public class MessagingAnnotationBeanPostProcessor
 
 	private final Map<Class<? extends Annotation>, MethodAnnotationPostProcessor<?>> postProcessors;
 
-	private final List<Runnable> methodsToPostProcessAfterContextInitialization = new ArrayList<>();
+	private final List<Runnable> methodsToPostProcessAfterContextInitialization;
 
 	@SuppressWarnings("NullAway.Init")
 	private ConfigurableListableBeanFactory beanFactory;
@@ -74,6 +74,7 @@ public MessagingAnnotationBeanPostProcessor(
 			Map<Class<? extends Annotation>, MethodAnnotationPostProcessor<?>> postProcessors) {
 
 		this.postProcessors = postProcessors;
+		this.methodsToPostProcessAfterContextInitialization = new ArrayList<>(this.postProcessors.size());
 	}
 
 	@Override
@@ -217,7 +218,7 @@ public void afterSingletonsInstantiated() {
 	protected static List<MessagingMetaAnnotation> obtainMessagingAnnotations(
 			Set<Class<? extends Annotation>> postProcessors, MergedAnnotations annotations, String identified) {
 
-		List<MessagingMetaAnnotation> messagingAnnotations = new ArrayList<>();
+		List<MessagingMetaAnnotation> messagingAnnotations = new ArrayList<>(postProcessors.size());
 
 		for (Class<? extends Annotation> annotationType : postProcessors) {
 			annotations.stream()

spring-integration-core/src/main/java/org/springframework/integration/dispatcher/PartitionedDispatcher.java

@@ -58,9 +58,9 @@
  */
 public class PartitionedDispatcher extends AbstractDispatcher {
 
-	private final List<UnicastingDispatcher> partitions = new ArrayList<>();
+	private final List<UnicastingDispatcher> partitions;
 
-	private final List<ExecutorService> executors = new ArrayList<>();
+	private final List<ExecutorService> executors;
 
 	private final int partitionCount;
 
@@ -79,7 +79,7 @@ public class PartitionedDispatcher extends AbstractDispatcher {
 	private final Lock lock = new ReentrantLock();
 
 	/**
-	 * Instantiate based on a provided number of partitions and function for partition key against
+	 * Instantiate based on a provided number of partitions and function for a partition key against
 	 * the message to dispatch.
 	 * @param partitionCount the number of partitions in this channel.
 	 * @param partitionKeyFunction the function to resolve a partition key against the message
@@ -90,6 +90,8 @@ public PartitionedDispatcher(int partitionCount, Function<Message<?>, Object> pa
 		Assert.notNull(partitionKeyFunction, "'partitionKeyFunction' must not be null");
 		this.partitionKeyFunction = partitionKeyFunction;
 		this.partitionCount = partitionCount;
+		this.partitions = new ArrayList<>(partitionCount);
+		this.executors = new ArrayList<>(partitionCount);
 	}
 
 	/**
@@ -143,7 +145,7 @@ public void setErrorHandler(ErrorHandler errorHandler) {
 
 	/**
 	 * Set a {@link MessageHandlingTaskDecorator} to wrap a message handling task into some
-	 * addition logic, e.g. message channel may provide an interception for its operations.
+	 * addition logic, e.g., a message channel may provide an interception for its operations.
 	 * @param messageHandlingTaskDecorator the {@link MessageHandlingTaskDecorator} to use.
 	 */
 	public void setMessageHandlingTaskDecorator(MessageHandlingTaskDecorator messageHandlingTaskDecorator) {
@@ -153,7 +155,7 @@ public void setMessageHandlingTaskDecorator(MessageHandlingTaskDecorator message
 
 	/**
 	 * Shutdown this dispatcher on application close.
-	 * The partition executors are shutdown and internal state of this instance is cleared.
+	 * The partition executors are shutdown and the internal state of this instance is cleared.
 	 */
 	public void shutdown() {
 		this.executors.forEach(ExecutorService::shutdown);