Nullability fine-tuning around bean properties

Issue: SPR-15720
Issue: SPR-15792

spring-messaging/src/main/java/org/springframework/messaging/handler/invocation/AbstractMethodMessageHandler.java

@@ -232,11 +232,15 @@ public abstract class AbstractMethodMessageHandler<T>
 			this.returnValueHandlers.addHandlers(initReturnValueHandlers());
 		}
 
-		for (String beanName : this.applicationContext.getBeanNamesForType(Object.class)) {
+		ApplicationContext context = getApplicationContext();
+		if (context == null) {
+			return;
+		}
+		for (String beanName : context.getBeanNamesForType(Object.class)) {
 			if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
 				Class<?> beanType = null;
 				try {
-					beanType = this.applicationContext.getType(beanName);
+					beanType = context.getType(beanName);
 				}
 				catch (Throwable ex) {
 					// An unresolvable bean type, probably from a lazy bean - let's ignore it.
@@ -279,8 +283,15 @@ public abstract class AbstractMethodMessageHandler<T>
 	 * @param handler the handler to check, either an instance of a Spring bean name
 	 */
 	protected final void detectHandlerMethods(final Object handler) {
-		Class<?> handlerType = (handler instanceof String ?
-				this.applicationContext.getType((String) handler) : handler.getClass());
+		Class<?> handlerType;
+		if (handler instanceof String) {
+			ApplicationContext context = getApplicationContext();
+			Assert.state(context != null, "ApplicationContext is required for resolving handler bean names");
+			handlerType = context.getType((String) handler);
+		}
+		else {
+			handlerType = handler.getClass();
+		}
 
 		if (handlerType != null) {
 			final Class<?> userType = ClassUtils.getUserClass(handlerType);
@@ -338,9 +349,10 @@ public abstract class AbstractMethodMessageHandler<T>
 	protected HandlerMethod createHandlerMethod(Object handler, Method method) {
 		HandlerMethod handlerMethod;
 		if (handler instanceof String) {
+			ApplicationContext context = getApplicationContext();
+			Assert.state(context != null, "ApplicationContext is required for resolving handler bean names");
 			String beanName = (String) handler;
-			handlerMethod = new HandlerMethod(beanName,
-					this.applicationContext.getAutowireCapableBeanFactory(), method);
+			handlerMethod = new HandlerMethod(beanName, context.getAutowireCapableBeanFactory(), method);
 		}
 		else {
 			handlerMethod = new HandlerMethod(handler, method);
@@ -645,7 +657,7 @@ public abstract class AbstractMethodMessageHandler<T>
 		}
 
 		@Override
-		public void onSuccess(Object result) {
+		public void onSuccess(@Nullable Object result) {
 			try {
 				MethodParameter returnType = this.handlerMethod.getAsyncReturnValueType(result);
 				returnValueHandlers.handleReturnValue(result, returnType, this.message);

spring-messaging/src/main/java/org/springframework/messaging/handler/invocation/InvocableHandlerMethod.java

@@ -252,7 +252,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 	}
 
 
-	MethodParameter getAsyncReturnValueType(Object returnValue) {
+	MethodParameter getAsyncReturnValueType(@Nullable Object returnValue) {
 		return new AsyncResultMethodParameter(returnValue);
 	}
 
@@ -264,7 +264,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 		private final ResolvableType returnType;
 
-		public AsyncResultMethodParameter(Object returnValue) {
+		public AsyncResultMethodParameter(@Nullable Object returnValue) {
 			super(-1);
 			this.returnValue = returnValue;
 			this.returnType = ResolvableType.forType(super.getGenericParameterType()).getGeneric();

spring-messaging/src/main/java/org/springframework/messaging/simp/SimpMessagingTemplate.java

@@ -54,6 +54,7 @@ public class SimpMessagingTemplate extends AbstractMessageSendingTemplate<String
 
 	private volatile long sendTimeout = -1;
 
+	@Nullable
 	private MessageHeaderInitializer headerInitializer;
 
 

spring-messaging/src/main/java/org/springframework/messaging/simp/annotation/support/SimpAnnotationMethodMessageHandler.java

@@ -26,6 +26,7 @@ import java.util.Map;
 import java.util.Set;
 
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
+import org.springframework.context.ApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.EmbeddedValueResolverAware;
 import org.springframework.context.SmartLifecycle;
@@ -305,8 +306,9 @@ public class SimpAnnotationMethodMessageHandler extends AbstractMethodMessageHan
 
 
 	protected List<HandlerMethodArgumentResolver> initArgumentResolvers() {
-		ConfigurableBeanFactory beanFactory = (getApplicationContext() instanceof ConfigurableApplicationContext ?
-				((ConfigurableApplicationContext) getApplicationContext()).getBeanFactory() : null);
+		ApplicationContext context = getApplicationContext();
+		ConfigurableBeanFactory beanFactory = (context instanceof ConfigurableApplicationContext ?
+				((ConfigurableApplicationContext) context).getBeanFactory() : null);
 
 		List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();
 

spring-messaging/src/main/java/org/springframework/messaging/support/IdTimestampMessageHeaderInitializer.java

@@ -16,8 +16,6 @@
 
 package org.springframework.messaging.support;
 
-import java.util.UUID;
-
 import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessageHeaders;
 import org.springframework.util.IdGenerator;
@@ -31,6 +29,10 @@ import org.springframework.util.IdGenerator;
  */
 public class IdTimestampMessageHeaderInitializer implements MessageHeaderInitializer {
 
+	private static final IdGenerator ID_VALUE_NONE_GENERATOR = () -> MessageHeaders.ID_VALUE_NONE;
+
+
+	@Nullable
 	private IdGenerator idGenerator;
 
 	private boolean enableTimestamp;
@@ -41,20 +43,12 @@ public class IdTimestampMessageHeaderInitializer implements MessageHeaderInitial
 	 * instances with.
 	 * <p>By default this property is set to {@code null} in which case the default
 	 * IdGenerator of {@link org.springframework.messaging.MessageHeaders} is used.
-	 * <p>To have no id's generated at all, see {@link #setDisableIdGeneration()}.
+	 * <p>To have no ids generated at all, see {@link #setDisableIdGeneration()}.
 	 */
 	public void setIdGenerator(@Nullable IdGenerator idGenerator) {
 		this.idGenerator = idGenerator;
 	}
 
-	/**
-	 * A shortcut for calling {@link #setIdGenerator(org.springframework.util.IdGenerator)}
-	 * with an id generation strategy to disable id generation completely.
-	 */
-	public void setDisableIdGeneration() {
-		this.idGenerator = ID_VALUE_NONE_GENERATOR;
-	}
-
 	/**
 	 * Return the configured {@code IdGenerator}, if any.
 	 */
@@ -63,6 +57,14 @@ public class IdTimestampMessageHeaderInitializer implements MessageHeaderInitial
 		return this.idGenerator;
 	}
 
+	/**
+	 * A shortcut for calling {@link #setIdGenerator} with an id generation strategy
+	 * to disable id generation completely.
+	 */
+	public void setDisableIdGeneration() {
+		this.idGenerator = ID_VALUE_NONE_GENERATOR;
+	}
+
 	/**
 	 * Whether to enable the automatic addition of the
 	 * {@link org.springframework.messaging.MessageHeaders#TIMESTAMP} header on
@@ -90,12 +92,4 @@ public class IdTimestampMessageHeaderInitializer implements MessageHeaderInitial
 		headerAccessor.setEnableTimestamp(isEnableTimestamp());
 	}
 
-
-	private static final IdGenerator ID_VALUE_NONE_GENERATOR = new IdGenerator() {
-		@Override
-		public UUID generateId() {
-			return MessageHeaders.ID_VALUE_NONE;
-		}
-	};
-
 }

spring-messaging/src/main/java/org/springframework/messaging/tcp/reactor/AbstractMonoToListenableFutureAdapter.java

@@ -24,6 +24,7 @@ import java.util.concurrent.TimeoutException;
 import reactor.core.publisher.Mono;
 import reactor.core.publisher.MonoProcessor;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.concurrent.FailureCallback;
 import org.springframework.util.concurrent.ListenableFuture;
@@ -67,12 +68,14 @@ abstract class AbstractMonoToListenableFutureAdapter<S, T> implements Listenable
 
 
 	@Override
+	@Nullable
 	public T get() throws InterruptedException {
 		S result = this.monoProcessor.block();
 		return adapt(result);
 	}
 
 	@Override
+	@Nullable
 	public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
 		Assert.notNull(unit, "TimeUnit must not be null");
 		Duration duration = Duration.ofMillis(TimeUnit.MILLISECONDS.convert(timeout, unit));
@@ -111,6 +114,7 @@ abstract class AbstractMonoToListenableFutureAdapter<S, T> implements Listenable
 	}
 
 
-	protected abstract T adapt(S result);
+	@Nullable
+	protected abstract T adapt(@Nullable S result);
 
 }

spring-messaging/src/main/java/org/springframework/messaging/tcp/reactor/MonoToListenableFutureAdapter.java

@@ -18,6 +18,8 @@ package org.springframework.messaging.tcp.reactor;
 
 import reactor.core.publisher.Mono;
 
+import org.springframework.lang.Nullable;
+
 /**
  * A Mono-to-ListenableFuture adapter where the source and the target from
  * the Promise and the ListenableFuture respectively are of the same type.
@@ -33,7 +35,7 @@ class MonoToListenableFutureAdapter<T> extends AbstractMonoToListenableFutureAda
 	}
 
 	@Override
-	protected T adapt(T result) {
+	protected T adapt(@Nullable T result) {
 		return result;
 	}