Replace isAssignableFrom() with isInstance() where feasible

Closes gh-36899

Signed-off-by: Yanming Zhou <zhouyanming@gmail.com>

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

@@ -36,7 +36,7 @@ public class SimpleHandlerAdapter implements HandlerAdapter {
 
 	@Override
 	public boolean supports(Object handler) {
-		return WebHandler.class.isAssignableFrom(handler.getClass());
+		return (handler instanceof WebHandler);
 	}
 
 	@Override

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

@@ -65,10 +65,10 @@ public class ErrorsMethodArgumentResolver extends HandlerMethodArgumentResolverS
 		// This is done to enable early argument resolution here. When the Mono actually
 		// completes it is replaced in the model with the actual value.
 
-		if (Mono.class.isAssignableFrom(errors.getClass())) {
+		if (errors instanceof Mono) {
 			return ((Mono<?>) errors).cast(Object.class);
 		}
-		else if (Errors.class.isAssignableFrom(errors.getClass())) {
+		else if (errors instanceof Errors) {
 			return Mono.just(errors);
 		}
 		else {

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

@@ -76,7 +76,7 @@ public class RequestAttributeMethodArgumentResolver extends AbstractNamedValueSy
 								parameter.getGenericParameterType() + " doesn't support empty values.");
 				return toAdapter.fromPublisher(Mono.empty());
 			}
-			if (parameter.getParameterType().isAssignableFrom(value.getClass())) {
+			if (parameter.getParameterType().isInstance(value)) {
 				return value;
 			}
 			ReactiveAdapter fromAdapter = getAdapterRegistry().getAdapter(value.getClass());

spring-webflux/src/main/java/org/springframework/web/reactive/socket/server/support/WebSocketHandlerAdapter.java

@@ -99,7 +99,7 @@ public class WebSocketHandlerAdapter implements HandlerAdapter, Ordered {
 
 	@Override
 	public boolean supports(Object handler) {
-		return WebSocketHandler.class.isAssignableFrom(handler.getClass());
+		return (handler instanceof WebSocketHandler);
 	}
 
 	@Override

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/HttpEntityMethodArgumentResolverTests.java

@@ -274,8 +274,7 @@ class HttpEntityMethodArgumentResolverTests {
 		Mono<Object> result = this.resolver.resolveArgument(param, new BindingContext(), exchange);
 		Object value = result.block(Duration.ofSeconds(5));
 
-		assertThat(value).isNotNull();
-		assertThat(param.getParameterType().isAssignableFrom(value.getClass())).as("Unexpected return value type: " + value.getClass()).isTrue();
+		assertThat(value).isInstanceOf(param.getParameterType());
 
 		return (T) value;
 	}

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/MessageReaderArgumentResolverTests.java

@@ -294,8 +294,7 @@ class MessageReaderArgumentResolverTests {
 		Mono<Object> result = this.resolver.readBody(param, true, this.bindingContext, exchange);
 		Object value = result.block(Duration.ofSeconds(5));
 
-		assertThat(value).isNotNull();
-		assertThat(param.getParameterType().isAssignableFrom(value.getClass())).as("Unexpected return value type: " + value).isTrue();
+		assertThat(value).isInstanceOf(param.getParameterType());
 
 		return (T) value;
 	}

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/RequestBodyMethodArgumentResolverTests.java

@@ -233,9 +233,7 @@ class RequestBodyMethodArgumentResolverTests {
 		Mono<Object> result = this.resolver.readBody(param, true, new BindingContext(), exchange);
 		Object value = result.block(Duration.ofSeconds(5));
 
-		assertThat(value).isNotNull();
-		assertThat(param.getParameterType().isAssignableFrom(value.getClass()))
-				.as("Unexpected return value type: " + value).isTrue();
+		assertThat(value).isInstanceOf(param.getParameterType());
 
 		//no inspection unchecked
 		return (T) value;
@@ -248,8 +246,7 @@ class RequestBodyMethodArgumentResolverTests {
 		Object value = result.block(Duration.ofSeconds(5));
 
 		if (value != null) {
-			assertThat(param.getParameterType().isAssignableFrom(value.getClass()))
-					.as("Unexpected parameter type: " + value).isTrue();
+			assertThat(value).isInstanceOf(param.getParameterType());
 		}
 
 		//no inspection unchecked

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/RequestPartMethodArgumentResolverTests.java

@@ -299,8 +299,7 @@ class RequestPartMethodArgumentResolverTests {
 		Mono<Object> result = this.resolver.resolveArgument(param, new BindingContext(), exchange);
 		Object value = result.block(Duration.ofSeconds(5));
 
-		assertThat(value).isNotNull();
-		assertThat(param.getParameterType().isAssignableFrom(value.getClass())).isTrue();
+		assertThat(value).isInstanceOf(param.getParameterType());
 		return (T) value;
 	}
 

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/WebSessionMethodArgumentResolverTests.java

@@ -67,14 +67,12 @@ class WebSessionMethodArgumentResolverTests {
 
 		param = this.testMethod.arg(Mono.class, WebSession.class);
 		actual = this.resolver.resolveArgument(param, context, exchange).block();
-		assertThat(actual).isNotNull();
-		assertThat(Mono.class.isAssignableFrom(actual.getClass())).isTrue();
+		assertThat(actual).isInstanceOf(Mono.class);
 		assertThat(((Mono<?>) actual).block()).isSameAs(session);
 
 		param = this.testMethod.arg(Single.class, WebSession.class);
 		actual = this.resolver.resolveArgument(param, context, exchange).block();
-		assertThat(actual).isNotNull();
-		assertThat(Single.class.isAssignableFrom(actual.getClass())).isTrue();
+		assertThat(actual).isInstanceOf(Single.class);
 		assertThat(((Single<?>) actual).blockingGet()).isSameAs(session);
 	}