GH-10083: Apply Nullability to core handler package

spring-integration-core/src/main/java/org/springframework/integration/core/ErrorMessagePublisher.java

@@ -70,7 +70,7 @@ public final void setErrorMessageStrategy(ErrorMessageStrategy errorMessageStrat
 		this.errorMessageStrategy = errorMessageStrategy;
 	}
 
-	public final void setChannel(MessageChannel channel) {
+	public final void setChannel(@Nullable MessageChannel channel) {
 		this.channel = channel;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/endpoint/MessageProcessorMessageSource.java

@@ -19,6 +19,8 @@
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.integration.handler.MessageProcessor;
+import org.springframework.integration.support.MutableMessageBuilder;
+import org.springframework.messaging.Message;
 
 /**
  * The {@link org.springframework.integration.core.MessageSource} strategy implementation
@@ -27,11 +29,15 @@
  *
  * @author Artem Bilan
  * @author Gary Russell
+ * @author Jiandong Ma
  *
  * @since 5.0
  */
 public class MessageProcessorMessageSource extends AbstractMessageSource<Object> {
 
+	// provide a fake message since the contract of processMessage requires a NonNull Message.
+	static final Message<Object> FAKE_MESSAGE = MutableMessageBuilder.withPayload(new Object(), false).build();
+
 	private final MessageProcessor<?> messageProcessor;
 
 	public MessageProcessorMessageSource(MessageProcessor<?> messageProcessor) {
@@ -45,7 +51,7 @@ public String getComponentType() {
 
 	@Override
 	protected @Nullable Object doReceive() {
-		return this.messageProcessor.processMessage(null);
+		return this.messageProcessor.processMessage(FAKE_MESSAGE);
 	}
 
 }

spring-integration-core/src/main/java/org/springframework/integration/filter/MessageFilter.java

@@ -176,7 +176,7 @@ public boolean isRunning() {
 	}
 
 	@Override
-	public Object postProcess(Message<?> message, Object result) {
+	public @Nullable Object postProcess(Message<?> message, @Nullable Object result) {
 		if (result == null) {
 			MessageChannel channelToDiscard = getDiscardChannel();
 			if (channelToDiscard != null) {

spring-integration-core/src/main/java/org/springframework/integration/handler/AbstractMessageHandler.java

@@ -55,7 +55,7 @@ public void setObservationConvention(@Nullable MessageReceiverObservationConvent
 		this.observationConvention = observationConvention;
 	}
 
-	@Override // NOSONAR
+	@Override
 	public void handleMessage(Message<?> message) {
 		Assert.notNull(message, "Message must not be null");
 		if (isLoggingEnabled()) {

spring-integration-core/src/main/java/org/springframework/integration/handler/AbstractMessageProducingHandler.java

@@ -76,7 +76,7 @@
 public abstract class AbstractMessageProducingHandler extends AbstractMessageHandler
 		implements MessageProducer, HeaderPropagationAware {
 
-	protected final MessagingTemplate messagingTemplate = new MessagingTemplate(); // NOSONAR final
+	protected final MessagingTemplate messagingTemplate = new MessagingTemplate();
 
 	private boolean async;
 
@@ -88,7 +88,7 @@ public abstract class AbstractMessageProducingHandler extends AbstractMessageHan
 	@Nullable
 	private MessageChannel outputChannel;
 
-	private String[] notPropagatedHeaders;
+	private String @Nullable [] notPropagatedHeaders;
 
 	private boolean selectiveHeaderPropagation;
 
@@ -113,7 +113,7 @@ public void setOutputChannel(MessageChannel outputChannel) {
 	@Override
 	public void setOutputChannelName(String outputChannelName) {
 		Assert.hasText(outputChannelName, "'outputChannelName' must not be empty");
-		this.outputChannelName = outputChannelName; //NOSONAR (inconsistent sync)
+		this.outputChannelName = outputChannelName;
 	}
 
 	/**
@@ -213,12 +213,10 @@ public void addNotPropagatedHeaders(String... headers) {
 	@Override
 	protected void onInit() {
 		super.onInit();
-		Assert.state(!(this.outputChannelName != null && this.outputChannel != null), //NOSONAR (inconsistent sync)
+		Assert.state(!(this.outputChannelName != null && this.outputChannel != null),
 				"'outputChannelName' and 'outputChannel' are mutually exclusive.");
 		BeanFactory beanFactory = getBeanFactory();
-		if (beanFactory != null) {
-			this.messagingTemplate.setBeanFactory(beanFactory);
-		}
+		this.messagingTemplate.setBeanFactory(beanFactory);
 		this.messagingTemplate.setDestinationResolver(getChannelResolver());
 		setAsyncIfCan();
 		if (!this.sendTimeoutSet) {
@@ -244,9 +242,9 @@ public MessageChannel getOutputChannel() {
 		return this.outputChannel;
 	}
 
-	protected void sendOutputs(Object result, Message<?> requestMessage) {
-		if (result instanceof Iterable<?> && shouldSplitOutput((Iterable<?>) result)) {
-			for (Object o : (Iterable<?>) result) {
+	protected void sendOutputs(@Nullable Object result, Message<?> requestMessage) {
+		if (result instanceof Iterable<?> iterableResult && shouldSplitOutput(iterableResult)) {
+			for (Object o : iterableResult) {
 				produceOutput(o, requestMessage);
 			}
 		}
@@ -294,13 +292,12 @@ protected void produceOutput(Object replyArg, final Message<?> requestMessage) {
 	private Map<?, ?> obtainRoutingSlipHeader(MessageHeaders requestHeaders, Object reply) {
 		Map<?, ?> routingSlipHeader = requestHeaders.get(IntegrationMessageHeaderAccessor.ROUTING_SLIP, Map.class);
 		if (routingSlipHeader == null) {
-			if (reply instanceof Message) {
-				routingSlipHeader = ((Message<?>) reply).getHeaders()
+			if (reply instanceof Message<?> replyMessage) {
+				routingSlipHeader = replyMessage.getHeaders()
 						.get(IntegrationMessageHeaderAccessor.ROUTING_SLIP, Map.class);
 			}
-			else if (reply instanceof AbstractIntegrationMessageBuilder<?>) {
-				routingSlipHeader = ((AbstractIntegrationMessageBuilder<?>) reply)
-						.getHeader(IntegrationMessageHeaderAccessor.ROUTING_SLIP, Map.class);
+			else if (reply instanceof AbstractIntegrationMessageBuilder<?> messageBuilder) {
+				routingSlipHeader = messageBuilder.getHeader(IntegrationMessageHeaderAccessor.ROUTING_SLIP, Map.class);
 			}
 		}
 		return routingSlipHeader;
@@ -310,12 +307,11 @@ else if (reply instanceof AbstractIntegrationMessageBuilder<?>) {
 	private Object obtainReplyChannel(MessageHeaders requestHeaders, Object reply) {
 		Object replyChannel = requestHeaders.getReplyChannel();
 		if (replyChannel == null) {
-			if (reply instanceof Message) {
-				replyChannel = ((Message<?>) reply).getHeaders().getReplyChannel();
+			if (reply instanceof Message<?> replyMessage) {
+				replyChannel = replyMessage.getHeaders().getReplyChannel();
 			}
-			else if (reply instanceof AbstractIntegrationMessageBuilder<?>) {
-				replyChannel = ((AbstractIntegrationMessageBuilder<?>) reply)
-						.getHeader(MessageHeaders.REPLY_CHANNEL, Object.class);
+			else if (reply instanceof AbstractIntegrationMessageBuilder<?> messageBuilder) {
+				replyChannel = messageBuilder.getHeader(MessageHeaders.REPLY_CHANNEL, Object.class);
 			}
 		}
 		return replyChannel;
@@ -438,15 +434,15 @@ else if (reply instanceof AbstractIntegrationMessageBuilder) {
 		return builder;
 	}
 
-	private Object getOutputChannelFromRoutingSlip(Object reply, Message<?> requestMessage, List<?> routingSlip,
+	private @Nullable Object getOutputChannelFromRoutingSlip(Object reply, Message<?> requestMessage, List<?> routingSlip,
 			AtomicInteger routingSlipIndex) {
 
 		if (routingSlipIndex.get() >= routingSlip.size()) {
 			return null;
 		}
 
 		Object path = routingSlip.get(routingSlipIndex.get());
-		Object routingSlipPathValue = null;
+		Object routingSlipPathValue;
 
 		if (path instanceof String string) {
 			routingSlipPathValue = getBeanFactory().getBean(string);
@@ -558,7 +554,7 @@ protected boolean shouldCopyRequestHeaders() {
 	protected void sendErrorMessage(Message<?> requestMessage, Throwable ex) {
 		Object errorChannel = resolveErrorChannel(requestMessage.getHeaders());
 		Throwable result = ex;
-		if (!(ex instanceof MessagingException)) {
+		if (!(result instanceof MessagingException)) {
 			result = new MessageHandlingException(requestMessage, ex);
 		}
 		if (errorChannel == null) {
@@ -578,7 +574,7 @@ protected void sendErrorMessage(Message<?> requestMessage, Throwable ex) {
 		}
 	}
 
-	protected Object resolveErrorChannel(final MessageHeaders requestHeaders) {
+	protected @Nullable Object resolveErrorChannel(final MessageHeaders requestHeaders) {
 		Object errorChannel = requestHeaders.getErrorChannel();
 		if (errorChannel == null) {
 			try {
@@ -594,12 +590,10 @@ protected Object resolveErrorChannel(final MessageHeaders requestHeaders) {
 	protected void setupMessageProcessor(MessageProcessor<?> processor) {
 		if (processor instanceof AbstractMessageProcessor<?> abstractMessageProcessor) {
 			ConversionService conversionService = getConversionService();
-			if (conversionService != null) {
-				abstractMessageProcessor.setConversionService(conversionService);
-			}
+			abstractMessageProcessor.setConversionService(conversionService);
 		}
 		BeanFactory beanFactory = getBeanFactory();
-		if (processor instanceof BeanFactoryAware beanFactoryAware && beanFactory != null) {
+		if (processor instanceof BeanFactoryAware beanFactoryAware) {
 			beanFactoryAware.setBeanFactory(beanFactory);
 		}
 		if (processor instanceof InitializingBean initializingBean) {
@@ -628,7 +622,7 @@ private final class ReplyFutureCallback implements BiConsumer<Object, Throwable>
 		}
 
 		@Override
-		public void accept(Object result, Throwable exception) {
+		public void accept(@Nullable Object result, @Nullable Throwable exception) {
 			if (result != null) {
 				Message<?> replyMessage = null;
 				try {
@@ -637,7 +631,7 @@ public void accept(Object result, Throwable exception) {
 				}
 				catch (Exception ex) {
 					Exception exceptionToLogAndSend = ex;
-					if (!(ex instanceof MessagingException)) { // NOSONAR
+					if (!(ex instanceof MessagingException)) {
 						exceptionToLogAndSend = new MessageHandlingException(this.requestMessage, ex);
 						if (replyMessage != null) {
 							exceptionToLogAndSend = new MessagingException(replyMessage, exceptionToLogAndSend);
@@ -648,7 +642,8 @@ public void accept(Object result, Throwable exception) {
 				}
 			}
 			else if (exception != null) {
-				onFailure(exception instanceof CompletionException ? exception.getCause() : exception);
+				onFailure(exception instanceof CompletionException && exception.getCause() != null
+						? exception.getCause() : exception);
 			}
 		}
 

spring-integration-core/src/main/java/org/springframework/integration/handler/AbstractReplyProducingMessageHandler.java

@@ -31,7 +31,6 @@
 import org.springframework.integration.handler.advice.HandleMessageAdvice;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
-import org.springframework.util.ClassUtils;
 
 /**
  * Base class for MessageHandlers that are capable of producing replies.
@@ -53,11 +52,12 @@ public abstract class AbstractReplyProducingMessageHandler extends AbstractMessa
 
 	private final List<Advice> adviceChain = new LinkedList<>();
 
-	private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();
+	@SuppressWarnings("NullAway.Init")
+	private ClassLoader beanClassLoader;
 
 	private boolean requiresReply = false;
 
-	private volatile RequestHandler advisedRequestHandler;
+	private volatile @Nullable RequestHandler advisedRequestHandler;
 
 	/**
 	 * Flag whether a reply is required. If true an incoming message MUST result in a reply message being sent.
@@ -160,8 +160,8 @@ else if (!isAsync() && isLoggingEnabled()) {
 		}
 	}
 
-	@Nullable
-	protected Object doInvokeAdvisedRequestHandler(Message<?> message) {
+	@SuppressWarnings("NullAway") // dataflow analysis limitation
+	protected @Nullable Object doInvokeAdvisedRequestHandler(Message<?> message) {
 		return this.advisedRequestHandler.handleRequestMessage(message);
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/handler/BeanNameMessageProcessor.java

@@ -37,13 +37,15 @@ public class BeanNameMessageProcessor<T> implements MessageProcessor<T>, BeanFac
 
 	private final String beanName;
 
-	private final String methodName;
+	private final @Nullable String methodName;
 
+	@SuppressWarnings("NullAway.Init")
 	private MessageProcessor<T> delegate;
 
+	@SuppressWarnings("NullAway.Init")
 	private BeanFactory beanFactory;
 
-	public BeanNameMessageProcessor(String object, String methodName) {
+	public BeanNameMessageProcessor(String object, @Nullable String methodName) {
 		this.beanName = object;
 		this.methodName = methodName;
 	}

spring-integration-core/src/main/java/org/springframework/integration/handler/ControlBusMessageProcessor.java

@@ -18,6 +18,8 @@
 
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.expression.Expression;
 import org.springframework.integration.IntegrationMessageHeaderAccessor;
 import org.springframework.integration.IntegrationPattern;
@@ -41,6 +43,7 @@
 public class ControlBusMessageProcessor extends AbstractMessageProcessor<Object>
 		implements IntegrationPattern {
 
+	@SuppressWarnings("NullAway.Init")
 	private ControlBusCommandRegistry controlBusCommandRegistry;
 
 	public ControlBusMessageProcessor() {
@@ -69,7 +72,7 @@ protected void onInit() {
 	}
 
 	@Override
-	public Object processMessage(Message<?> message) {
+	public @Nullable Object processMessage(Message<?> message) {
 		String command = message.getPayload().toString();
 		@SuppressWarnings("unchecked")
 		List<Object> arguments =