GH-10083: Apply Nullability to core dispatcher package

Related to: #10083

* Due to the high use of the `dispatch` method it is better to suppress the `NullAway` error, than take the performance hit of using `requiresNonNull`
* Add comment to `PartitionedDispatcher.dispatch` stating why a `@SuppressWarning` is needed.
* Correct comment PartitionedDispatcher.dispatch to state that partitionsMap never returns null.
`PartititonDispatcher.partition` will always return at least 1 partition.

Author: cppwfs

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

@@ -22,6 +22,7 @@
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.integration.support.utils.IntegrationUtils;
 import org.springframework.messaging.Message;
@@ -53,7 +54,7 @@ public abstract class AbstractDispatcher implements MessageDispatcher {
 
 	private volatile int maxSubscribers = Integer.MAX_VALUE;
 
-	private volatile MessageHandler theOneHandler;
+	private volatile @Nullable MessageHandler theOneHandler;
 
 	private final Lock lock = new ReentrantLock();
 

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

@@ -19,6 +19,8 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageDeliveryException;
 import org.springframework.util.StringUtils;
@@ -30,6 +32,7 @@
  * @author Mark Fisher
  * @author Artem Bilan
  * @author Gary Russell
+ * @author Glenn Renfro
  *
  * @since 1.0.3
  */
@@ -69,7 +72,7 @@ public String getMessage() {
 		return message.toString();
 	}
 
-	private String appendPeriodIfNecessary(String baseMessage) {
+	private String appendPeriodIfNecessary(@Nullable String baseMessage) {
 		if (!StringUtils.hasText(baseMessage)) {
 			return "";
 		}

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

@@ -20,6 +20,8 @@
 import java.util.UUID;
 import java.util.concurrent.Executor;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
@@ -56,12 +58,13 @@
  * @author Gary Russell
  * @author Oleg Zhurakousky
  * @author Artem Bilan
+ * @author Glenn Renfro
  */
 public class BroadcastingDispatcher extends AbstractDispatcher implements BeanFactoryAware {
 
 	private final boolean requireSubscribers;
 
-	private final Executor executor;
+	private final @Nullable Executor executor;
 
 	private boolean ignoreFailures;
 
@@ -71,6 +74,7 @@ public class BroadcastingDispatcher extends AbstractDispatcher implements BeanFa
 
 	private MessageHandlingTaskDecorator messageHandlingTaskDecorator = task -> task;
 
+	@SuppressWarnings("NullAway.Init")
 	private BeanFactory beanFactory;
 
 	private volatile MessageBuilderFactory messageBuilderFactory = new DefaultMessageBuilderFactory();
@@ -89,7 +93,7 @@ public BroadcastingDispatcher(boolean requireSubscribers) {
 		this(null, requireSubscribers);
 	}
 
-	public BroadcastingDispatcher(Executor executor, boolean requireSubscribers) {
+	public BroadcastingDispatcher(@Nullable Executor executor, boolean requireSubscribers) {
 		this.requireSubscribers = requireSubscribers;
 		this.executor = executor;
 	}

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

@@ -54,6 +54,7 @@
  *
  * @author Artem Bilan
  * @author Christian Tzolov
+ * @author Glenn Renfro
  *
  * @since 6.1
  */
@@ -71,10 +72,9 @@ public class PartitionedDispatcher extends AbstractDispatcher {
 
 	private Predicate<Exception> failoverStrategy = (exception) -> true;
 
-	@Nullable
-	private LoadBalancingStrategy loadBalancingStrategy;
+	private @Nullable LoadBalancingStrategy loadBalancingStrategy;
 
-	private ErrorHandler errorHandler;
+	private @Nullable ErrorHandler errorHandler;
 
 	private MessageHandlingTaskDecorator messageHandlingTaskDecorator = task -> task;
 
@@ -164,6 +164,7 @@ public void shutdown() {
 	}
 
 	@Override
+	@SuppressWarnings("NullAway") // The partitions map never returns null according to partition hash
 	public boolean dispatch(Message<?> message) {
 		populatedPartitions();
 		int partition = Math.abs(this.partitionKeyFunction.apply(message).hashCode()) % this.partitionCount;

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

@@ -51,18 +51,19 @@
  * @author Gary Russell
  * @author Oleg Zhurakousky
  * @author Artem Bilan
+ * @author Glenn Renfro
  *
  * @since 1.0.2
  */
 public class UnicastingDispatcher extends AbstractDispatcher {
 
 	private final MessageHandler dispatchHandler = this::doDispatch;
 
-	private final Executor executor;
+	private final @Nullable Executor executor;
 
 	private Predicate<Exception> failoverStrategy = (exception) -> true;
 
-	private LoadBalancingStrategy loadBalancingStrategy;
+	private @Nullable LoadBalancingStrategy loadBalancingStrategy;
 
 	private MessageHandlingTaskDecorator messageHandlingTaskDecorator = task -> task;
 

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

@@ -1,4 +1,5 @@
 /**
  * Provides classes related to dispatching messages.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.dispatcher;