Further refactoring of ReactiveAdapter/Registry

Simplify getAdapterFrom/To into a single getAdapter method that looks
for an exact match by type first and then isAssignableFrom.

Also expose shortcut methods in ReactiveAdapter to minimize the need
for access to the ReactiveTypeDescriptor.

Issue: SPR-14902

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

@@ -70,6 +70,35 @@ public class ReactiveAdapter {
 		return this.descriptor;
 	}
 
+	/**
+	 * A shortcut for {@code getDescriptor().getReactiveType()}.
+	 */
+	public Class<?> getReactiveType() {
+		return getDescriptor().getReactiveType();
+	}
+
+	/**
+	 * A shortcut for {@code getDescriptor().isMultiValue()}.
+	 */
+	public boolean isMultiValue() {
+		return getDescriptor().isMultiValue();
+	}
+
+	/**
+	 * A shortcut for {@code getDescriptor().supportsEmpty()}.
+	 */
+	public boolean supportsEmpty() {
+		return getDescriptor().supportsEmpty();
+	}
+
+	/**
+	 * A shortcut for {@code getDescriptor().isNoValue()}.
+	 */
+	public boolean isNoValue() {
+		return getDescriptor().isNoValue();
+	}
+
+
 	/**
 	 * Adapt the given instance to a Reactive Streams Publisher.
 	 * @param source the source object to adapt from

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

@@ -21,7 +21,6 @@ import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 import java.util.function.Function;
-import java.util.function.Predicate;
 
 import io.reactivex.BackpressureStrategy;
 import io.reactivex.Completable;
@@ -101,34 +100,31 @@ public class ReactiveAdapterRegistry {
 	}
 
 	/**
-	 * Get the adapter to use to adapt from the given reactive type.
+	 * Get the adapter for the given reactive type.
 	 */
-	public ReactiveAdapter getAdapterFrom(Class<?> reactiveType) {
-		return getAdapterFrom(reactiveType, null);
+	public ReactiveAdapter getAdapter(Class<?> reactiveType) {
+		return getAdapter(reactiveType, null);
 	}
 
 	/**
-	 * Get the adapter to use to adapt from the given reactive type. Or if the
-	 * "source" object is not {@code null} its actual type is used instead.
+	 * Get the adapter for the given reactive type. Or if a "source" object is
+	 * provided, its actual type is used instead.
+	 * @param reactiveType the reactive type
+	 * @param source an instance of the reactive type (i.e. to adapt from)
 	 */
-	public ReactiveAdapter getAdapterFrom(Class<?> reactiveType, Object source) {
+	public ReactiveAdapter getAdapter(Class<?> reactiveType, Object source) {
+
 		source = (source instanceof Optional ? ((Optional<?>) source).orElse(null) : source);
 		Class<?> clazz = (source != null ? source.getClass() : reactiveType);
-		return getAdapter(type -> type.isAssignableFrom(clazz));
-	}
 
-	/**
-	 * Get the adapter for the given reactive type to adapt to.
-	 */
-	public ReactiveAdapter getAdapterTo(Class<?> reactiveType) {
-		return getAdapter(reactiveType::equals);
-	}
-
-	private ReactiveAdapter getAdapter(Predicate<Class<?>> predicate) {
 		return this.adapters.stream()
-				.filter(adapter -> predicate.test(adapter.getDescriptor().getReactiveType()))
+				.filter(adapter -> adapter.getReactiveType().equals(clazz))
 				.findFirst()
-				.orElse(null);
+				.orElseGet(() ->
+						this.adapters.stream()
+								.filter(adapter -> adapter.getReactiveType().isAssignableFrom(clazz))
+								.findFirst()
+								.orElse(null));
 	}
 
 
@@ -233,7 +229,7 @@ public class ReactiveAdapterRegistry {
 		@Override
 		public <T> Publisher<T> toPublisher(Object source) {
 			Publisher<T> publisher = super.toPublisher(source);
-			return (getDescriptor().isMultiValue() ? Flux.from(publisher) : Mono.from(publisher));
+			return (isMultiValue() ? Flux.from(publisher) : Mono.from(publisher));
 		}
 	}