Introduce ResolvableType.toClass() shortcut

Issue: SPR-17086

Author: jhoeller

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

@@ -159,12 +159,12 @@ private static boolean isResolvedTypeMatch(Method genericMethod, Method candidat
 			Class<?> candidateParameter = candidateParameters[i];
 			if (candidateParameter.isArray()) {
 				// An array type: compare the component type.
-				if (!candidateParameter.getComponentType().equals(genericParameter.getComponentType().resolve(Object.class))) {
+				if (!candidateParameter.getComponentType().equals(genericParameter.getComponentType().toClass())) {
 					return false;
 				}
 			}
 			// A non-array type: compare the type itself.
-			if (!candidateParameter.equals(genericParameter.resolve(Object.class))) {
+			if (!candidateParameter.equals(genericParameter.toClass())) {
 				return false;
 			}
 		}

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

@@ -212,7 +212,7 @@ else if (Collection.class.isAssignableFrom(resolvedType)) {
 				ReactiveAdapter adapter = reactiveAdapterRegistry.getAdapter(valueClass);
 				if (adapter != null && !adapter.getDescriptor().isNoValue()) {
 					reactiveSuffix = ClassUtils.getShortName(valueClass);
-					valueClass = ResolvableType.forMethodReturnType(method).getGeneric().resolve(Object.class);
+					valueClass = ResolvableType.forMethodReturnType(method).getGeneric().toClass();
 				}
 			}
 		}

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

@@ -229,7 +229,7 @@ private static ResolvableType resolveVariable(TypeVariable<?> typeVariable, Reso
 	 */
 	@SuppressWarnings("rawtypes")
 	public static Class<?> resolveType(Type genericType, Map<TypeVariable, Type> map) {
-		return ResolvableType.forType(genericType, new TypeVariableMapVariableResolver(map)).resolve(Object.class);
+		return ResolvableType.forType(genericType, new TypeVariableMapVariableResolver(map)).toClass();
 	}
 
 	/**

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

@@ -229,6 +229,18 @@ public Object getSource() {
 		return (source != null ? source : this.type);
 	}
 
+	/**
+	 * Return this type as a resolved {@code Class}, falling back to
+	 * {@link java.lang.Object} if no specific class can be resolved.
+	 * @return the resolved {@link Class} or the {@code Object} fallback
+	 * @since 5.1
+	 * @see #getRawClass()
+	 * @see #resolve(Class)
+	 */
+	public Class<?> toClass() {
+		return resolve(Object.class);
+	}
+
 	/**
 	 * Determine whether the given object is an instance of this {@code ResolvableType}.
 	 * @param obj the object to check
@@ -328,7 +340,7 @@ private boolean isAssignableFrom(ResolvableType other, @Nullable Map<Type, Type>
 		if (ourResolved == null) {
 			ourResolved = resolve(Object.class);
 		}
-		Class<?> otherResolved = other.resolve(Object.class);
+		Class<?> otherResolved = other.toClass();
 
 		// We need an exact type match for generics
 		// List<CharSequence> is not assignable from List<String>

spring-core/src/main/java/org/springframework/core/codec/ByteArrayEncoder.java

@@ -43,7 +43,7 @@ public ByteArrayEncoder() {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		Class<?> clazz = elementType.resolve(Object.class);
+		Class<?> clazz = elementType.toClass();
 		return super.canEncode(elementType, mimeType) && byte[].class.isAssignableFrom(clazz);
 	}
 

spring-core/src/main/java/org/springframework/core/codec/ByteBufferEncoder.java

@@ -44,7 +44,7 @@ public ByteBufferEncoder() {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		Class<?> clazz = elementType.resolve(Object.class);
+		Class<?> clazz = elementType.toClass();
 		return super.canEncode(elementType, mimeType) && ByteBuffer.class.isAssignableFrom(clazz);
 	}
 

spring-core/src/main/java/org/springframework/core/codec/CharSequenceEncoder.java

@@ -56,7 +56,7 @@ private CharSequenceEncoder(MimeType... mimeTypes) {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		Class<?> clazz = elementType.resolve(Object.class);
+		Class<?> clazz = elementType.toClass();
 		return super.canEncode(elementType, mimeType) && CharSequence.class.isAssignableFrom(clazz);
 	}
 

spring-core/src/main/java/org/springframework/core/codec/DataBufferEncoder.java

@@ -43,7 +43,7 @@ public DataBufferEncoder() {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		Class<?> clazz = elementType.resolve(Object.class);
+		Class<?> clazz = elementType.toClass();
 		return super.canEncode(elementType, mimeType) && DataBuffer.class.isAssignableFrom(clazz);
 	}
 

spring-core/src/main/java/org/springframework/core/codec/ResourceEncoder.java

@@ -60,7 +60,7 @@ public ResourceEncoder(int bufferSize) {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		Class<?> clazz = elementType.resolve(Object.class);
+		Class<?> clazz = elementType.toClass();
 		return (super.canEncode(elementType, mimeType) && Resource.class.isAssignableFrom(clazz));
 	}
 

spring-core/src/main/java/org/springframework/core/codec/ResourceRegionEncoder.java

@@ -73,7 +73,7 @@ public ResourceRegionEncoder(int bufferSize) {
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		return super.canEncode(elementType, mimeType)
-				&& ResourceRegion.class.isAssignableFrom(elementType.resolve(Object.class));
+				&& ResourceRegion.class.isAssignableFrom(elementType.toClass());
 	}
 
 	@Override

spring-core/src/main/java/org/springframework/core/convert/TypeDescriptor.java

@@ -120,7 +120,7 @@ public TypeDescriptor(Property property) {
 	 */
 	protected TypeDescriptor(ResolvableType resolvableType, @Nullable Class<?> type, @Nullable Annotation[] annotations) {
 		this.resolvableType = resolvableType;
-		this.type = (type != null ? type : resolvableType.resolve(Object.class));
+		this.type = (type != null ? type : resolvableType.toClass());
 		this.annotatedElement = new AnnotatedElementAdapter(annotations);
 	}
 

spring-core/src/main/java/org/springframework/core/convert/support/GenericConversionService.java

@@ -117,7 +117,7 @@ public void addConverterFactory(ConverterFactory<?, ?> factory) {
 					"ConverterFactory [" + factory.getClass().getName() + "]; does the class parameterize those types?");
 		}
 		addConverter(new ConverterFactoryAdapter(factory,
-				new ConvertiblePair(typeInfo[0].resolve(Object.class), typeInfo[1].resolve(Object.class))));
+				new ConvertiblePair(typeInfo[0].toClass(), typeInfo[1].toClass())));
 	}
 
 	@Override
@@ -351,7 +351,7 @@ private final class ConverterAdapter implements ConditionalGenericConverter {
 
 		public ConverterAdapter(Converter<?, ?> converter, ResolvableType sourceType, ResolvableType targetType) {
 			this.converter = (Converter<Object, Object>) converter;
-			this.typeInfo = new ConvertiblePair(sourceType.resolve(Object.class), targetType.resolve(Object.class));
+			this.typeInfo = new ConvertiblePair(sourceType.toClass(), targetType.toClass());
 			this.targetType = targetType;
 		}
 

spring-core/src/test/java/org/springframework/core/ResolvableTypeTests.java

@@ -619,7 +619,7 @@ public void resolveVariableGenericArrayUnknownWithFallback() throws Exception {
 		ResolvableType type = ResolvableType.forField(Fields.class.getField("variableTypeGenericArray"));
 		assertThat(type.getType().toString(), equalTo("T[]"));
 		assertThat(type.isArray(), equalTo(true));
-		assertThat(type.resolve(Object.class), equalTo((Class) Object.class));
+		assertThat(type.toClass(), equalTo((Class) Object.class));
 	}
 
 	@Test

spring-messaging/src/main/java/org/springframework/messaging/handler/annotation/support/MessageMethodArgumentResolver.java

@@ -97,7 +97,7 @@ public Object resolveArgument(MethodParameter parameter, Message<?> message) thr
 	private Class<?> getPayloadType(MethodParameter parameter) {
 		Type genericParamType = parameter.getGenericParameterType();
 		ResolvableType resolvableType = ResolvableType.forType(genericParamType).as(Message.class);
-		return resolvableType.getGeneric().resolve(Object.class);
+		return resolvableType.getGeneric().toClass();
 	}
 
 	/**

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

@@ -282,7 +282,7 @@ public Class<?> getParameterType() {
 				return this.returnValue.getClass();
 			}
 			if (!ResolvableType.NONE.equals(this.returnType)) {
-				return this.returnType.resolve(Object.class);
+				return this.returnType.toClass();
 			}
 			return super.getParameterType();
 		}

spring-web/src/main/java/org/springframework/http/codec/FormHttpMessageReader.java

@@ -84,7 +84,7 @@ public Charset getDefaultCharset() {
 	public boolean canRead(ResolvableType elementType, @Nullable MediaType mediaType) {
 		return ((MULTIVALUE_TYPE.isAssignableFrom(elementType) ||
 				(elementType.hasUnresolvableGenerics() &&
-						MultiValueMap.class.isAssignableFrom(elementType.resolve(Object.class)))) &&
+						MultiValueMap.class.isAssignableFrom(elementType.toClass()))) &&
 				(mediaType == null || MediaType.APPLICATION_FORM_URLENCODED.isCompatibleWith(mediaType)));
 	}
 

spring-web/src/main/java/org/springframework/http/codec/ServerSentEventHttpMessageWriter.java

@@ -93,7 +93,7 @@ public List<MediaType> getWritableMediaTypes() {
 	@Override
 	public boolean canWrite(ResolvableType elementType, @Nullable MediaType mediaType) {
 		return (mediaType == null || MediaType.TEXT_EVENT_STREAM.includes(mediaType) ||
-				ServerSentEvent.class.isAssignableFrom(elementType.resolve(Object.class)));
+				ServerSentEvent.class.isAssignableFrom(elementType.toClass()));
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/codec/json/AbstractJackson2Decoder.java

@@ -68,7 +68,7 @@ protected AbstractJackson2Decoder(ObjectMapper mapper, MimeType... mimeTypes) {
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		JavaType javaType = getObjectMapper().getTypeFactory().constructType(elementType.getType());
 		// Skip String: CharSequenceDecoder + "*/*" comes after
-		return (!CharSequence.class.isAssignableFrom(elementType.resolve(Object.class)) &&
+		return (!CharSequence.class.isAssignableFrom(elementType.toClass()) &&
 				getObjectMapper().canDeserialize(javaType) && supportsMimeType(mimeType));
 	}
 

spring-web/src/main/java/org/springframework/http/codec/json/AbstractJackson2Encoder.java

@@ -100,7 +100,7 @@ public void setStreamingMediaTypes(List<MediaType> mediaTypes) {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		Class<?> clazz = elementType.resolve(Object.class);
+		Class<?> clazz = elementType.toClass();
 		return supportsMimeType(mimeType) && (Object.class == clazz ||
 				(!String.class.isAssignableFrom(elementType.resolve(clazz)) && getObjectMapper().canSerialize(clazz)));
 	}

spring-web/src/main/java/org/springframework/http/codec/multipart/SynchronossPartHttpMessageReader.java

@@ -86,7 +86,7 @@ public List<MediaType> getReadableMediaTypes() {
 
 	@Override
 	public boolean canRead(ResolvableType elementType, @Nullable MediaType mediaType) {
-		return Part.class.equals(elementType.resolve(Object.class)) &&
+		return Part.class.equals(elementType.toClass()) &&
 				(mediaType == null || MediaType.MULTIPART_FORM_DATA.isCompatibleWith(mediaType));
 	}
 

spring-web/src/main/java/org/springframework/http/codec/xml/Jaxb2XmlEncoder.java

@@ -60,7 +60,7 @@ public Jaxb2XmlEncoder() {
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		if (super.canEncode(elementType, mimeType)) {
-			Class<?> outputClass = elementType.resolve(Object.class);
+			Class<?> outputClass = elementType.toClass();
 			return (outputClass.isAnnotationPresent(XmlRootElement.class) ||
 					outputClass.isAnnotationPresent(XmlType.class));
 		}

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ResponseEntityResultHandler.java

@@ -89,7 +89,7 @@ public boolean supports(HandlerResult result) {
 		}
 		ReactiveAdapter adapter = getAdapter(result);
 		return adapter != null && !adapter.isNoValue() &&
-				isSupportedType(result.getReturnType().getGeneric().resolve(Object.class));
+				isSupportedType(result.getReturnType().getGeneric().toClass());
 	}
 
 	@Nullable

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandler.java

@@ -157,7 +157,7 @@ public boolean supports(HandlerResult result) {
 			if (adapter.isNoValue()) {
 				return true;
 			}
-			type = result.getReturnType().getGeneric().resolve(Object.class);
+			type = result.getReturnType().getGeneric().toClass();
 		}
 
 		return (type != null &&

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/HttpEntityMethodProcessor.java

@@ -288,7 +288,7 @@ protected Class<?> getReturnValueType(@Nullable Object returnValue, MethodParame
 		else {
 			Type type = getHttpEntityType(returnType);
 			type = (type != null ? type : Object.class);
-			return ResolvableType.forMethodParameter(returnType, type).resolve(Object.class);
+			return ResolvableType.forMethodParameter(returnType, type).toClass();
 		}
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ReactiveTypeHandler.java

@@ -123,7 +123,7 @@ public ResponseBodyEmitter handleValue(Object returnValue, MethodParameter retur
 		Assert.state(adapter != null, "Unexpected return value: " + returnValue);
 
 		ResolvableType elementType = ResolvableType.forMethodParameter(returnType).getGeneric();
-		Class<?> elementClass = elementType.resolve(Object.class);
+		Class<?> elementClass = elementType.toClass();
 
 		Collection<MediaType> mediaTypes = getMediaTypes(request);
 		Optional<MediaType> mediaType = mediaTypes.stream().filter(MimeType::isConcrete).findFirst();

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ServletInvocableHandlerMethod.java

@@ -271,7 +271,7 @@ public Class<?> getParameterType() {
 				return this.returnValue.getClass();
 			}
 			if (!ResolvableType.NONE.equals(this.returnType)) {
-				return this.returnType.resolve(Object.class);
+				return this.returnType.toClass();
 			}
 			return super.getParameterType();
 		}