Consistently support CompletionStage in ReactiveAdapterRegistry

Aligns ReactiveAdapterRegistry with MVC/messaging handler methods in terms of recognizing CompletionStage as well as CompletableFuture. Includes consistent use of ReactiveAdapter for reactive transactions.

Closes gh-23011

spring-core/src/main/java/org/springframework/core/ReactiveAdapterRegistry.java

@@ -21,6 +21,7 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionStage;
 import java.util.function.Function;
 
 import io.reactivex.BackpressureStrategy;
@@ -221,12 +222,8 @@ public class ReactiveAdapterRegistry {
 					source -> source);
 
 			registry.registerReactiveType(
-					ReactiveTypeDescriptor.singleOptionalValue(CompletableFuture.class, () -> {
-						CompletableFuture<?> empty = new CompletableFuture<>();
-						empty.complete(null);
-						return empty;
-					}),
-					source -> Mono.fromFuture((CompletableFuture<?>) source),
+					ReactiveTypeDescriptor.singleOptionalValue(CompletionStage.class, EmptyCompletableFuture::new),
+					source -> Mono.fromCompletionStage((CompletionStage<?>) source),
 					source -> Mono.from(source).toFuture()
 			);
 		}
@@ -338,17 +335,28 @@ public class ReactiveAdapterRegistry {
 		}
 	}
 
+
+	private static class EmptyCompletableFuture<T> extends CompletableFuture<T> {
+
+		EmptyCompletableFuture() {
+			complete(null);
+		}
+	}
+
+
 	private static class CoroutinesRegistrar {
 
 		@SuppressWarnings("KotlinInternalInJava")
 		void registerAdapters(ReactiveAdapterRegistry registry) {
 			registry.registerReactiveType(
-					ReactiveTypeDescriptor.singleOptionalValue(Deferred.class, () -> CompletableDeferredKt.CompletableDeferred(null)),
+					ReactiveTypeDescriptor.singleOptionalValue(Deferred.class,
+							() -> CompletableDeferredKt.CompletableDeferred(null)),
 					source -> CoroutinesUtils.deferredToMono((Deferred<?>) source),
 					source -> CoroutinesUtils.monoToDeferred(Mono.from(source)));
 		}
 	}
 
+
 	private static class CoroutinesFlowRegistrar {
 
 		void registerAdapters(ReactiveAdapterRegistry registry) {

spring-tx/src/main/java/org/springframework/transaction/interceptor/TransactionAspectSupport.java

@@ -834,16 +834,13 @@ public abstract class TransactionAspectSupport implements BeanFactoryAware, Init
 				return TransactionContextManager.currentContext().flatMap(context ->
 						createTransactionIfNecessary(tm, txAttr, joinpointIdentification).flatMap(it -> {
 							try {
-								// This is an around advice: Invoke the next interceptor in the chain.
-								// This will normally result in a target object being invoked.
-								// Need re-wrapping of ReactiveTransaction until we get hold of the exception
-								// through usingWhen.
+								// Need re-wrapping until we get hold of the exception through usingWhen.
 								return Mono.<Object, ReactiveTransactionInfo>usingWhen(Mono.just(it), txInfo -> {
 									try {
 										return (Mono<?>) invocation.proceedWithInvocation();
 									}
-									catch (Throwable throwable) {
-										return Mono.error(throwable);
+									catch (Throwable ex) {
+										return Mono.error(ex);
 									}
 								}, this::commitTransactionAfterReturning, txInfo -> Mono.empty())
 										.onErrorResume(ex -> completeTransactionAfterThrowing(it, ex).then(Mono.error(ex)));
@@ -856,19 +853,17 @@ public abstract class TransactionAspectSupport implements BeanFactoryAware, Init
 						.subscriberContext(TransactionContextManager.getOrCreateContextHolder());
 			}
 
-			return TransactionContextManager.currentContext().flatMapMany(context ->
+			// Any other reactive type, typically a Flux
+			return this.adapter.fromPublisher(TransactionContextManager.currentContext().flatMapMany(context ->
 					createTransactionIfNecessary(tm, txAttr, joinpointIdentification).flatMapMany(it -> {
 						try {
-							// This is an around advice: Invoke the next interceptor in the chain.
-							// This will normally result in a target object being invoked.
-							// Need re-wrapping of ReactiveTransaction until we get hold of the exception
-							// through usingWhen.
+							// Need re-wrapping until we get hold of the exception through usingWhen.
 							return Flux.usingWhen(Mono.just(it), txInfo -> {
 								try {
 									return this.adapter.toPublisher(invocation.proceedWithInvocation());
 								}
-								catch (Throwable throwable) {
-									return Mono.error(throwable);
+								catch (Throwable ex) {
+									return Mono.error(ex);
 								}
 							}, this::commitTransactionAfterReturning, txInfo -> Mono.empty())
 									.onErrorResume(ex -> completeTransactionAfterThrowing(it, ex).then(Mono.error(ex)));
@@ -878,7 +873,7 @@ public abstract class TransactionAspectSupport implements BeanFactoryAware, Init
 							return completeTransactionAfterThrowing(it, ex).then(Mono.error(ex));
 						}
 					})).subscriberContext(TransactionContextManager.getOrCreateContext())
-					.subscriberContext(TransactionContextManager.getOrCreateContextHolder());
+					.subscriberContext(TransactionContextManager.getOrCreateContextHolder()));
 		}
 
 		@Nullable