Add shared instance of ReactiveAdapterRegistry

Issue: SPR-16218

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

@@ -59,7 +59,7 @@ public abstract class Conventions {
 	}
 
 	private static final ReactiveAdapterRegistry reactiveAdapterRegistry =
-			new ReactiveAdapterRegistry();
+			ReactiveAdapterRegistry.getSharedInstance();
 
 
 	/**

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

@@ -33,7 +33,10 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ReflectionUtils;
 
-import static org.springframework.core.ReactiveTypeDescriptor.*;
+import static org.springframework.core.ReactiveTypeDescriptor.multiValue;
+import static org.springframework.core.ReactiveTypeDescriptor.noValue;
+import static org.springframework.core.ReactiveTypeDescriptor.singleOptionalValue;
+import static org.springframework.core.ReactiveTypeDescriptor.singleRequiredValue;
 
 /**
  * A registry of adapters to adapt a Reactive Streams {@link Publisher} to/from
@@ -50,6 +53,9 @@ import static org.springframework.core.ReactiveTypeDescriptor.*;
  */
 public class ReactiveAdapterRegistry {
 
+	@Nullable
+	private static volatile ReactiveAdapterRegistry sharedInstance;
+
 	private final boolean reactorPresent;
 
 	private final List<ReactiveAdapter> adapters = new ArrayList<>(32);
@@ -98,6 +104,31 @@ public class ReactiveAdapterRegistry {
 	}
 
 
+	/**
+	 * Return a shared default {@code ReactiveAdapterRegistry} instance, lazily
+	 * building it once needed.
+	 * <p><b>NOTE:</b> We highly recommend passing a long-lived, pre-configured
+	 * {@code ReactiveAdapterRegistry} instance for customization purposes.
+	 * This accessor is only meant as a fallback for code paths that want to
+	 * fall back on a default instance if one isn't provided.
+	 * @return the shared {@code ReactiveAdapterRegistry} instance (never {@code null})
+	 * @since 5.0.2
+	 */
+	public static ReactiveAdapterRegistry getSharedInstance() {
+		ReactiveAdapterRegistry ar = sharedInstance;
+		if (ar == null) {
+			synchronized (ReactiveAdapterRegistry.class) {
+				ar = sharedInstance;
+				if (ar == null) {
+					ar = new ReactiveAdapterRegistry();
+					sharedInstance = ar;
+				}
+			}
+		}
+		return ar;
+	}
+
+
 	/**
 	 * Whether the registry has any adapters which would be the case if any of
 	 * Reactor, RxJava 2, or RxJava 1 (+ RxJava Reactive Streams bridge) are

spring-core/src/test/java/org/springframework/core/convert/support/ReactiveAdapterRegistryTests.java

@@ -50,7 +50,7 @@ import static org.junit.Assert.assertTrue;
 @SuppressWarnings("unchecked")
 public class ReactiveAdapterRegistryTests {
 
-	private final ReactiveAdapterRegistry registry = new ReactiveAdapterRegistry();
+	private final ReactiveAdapterRegistry registry = ReactiveAdapterRegistry.getSharedInstance();
 
 
 	@Test

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

@@ -66,7 +66,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 
 	private ParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();
 
-	private ReactiveAdapterRegistry reactiveAdapterRegistry = new ReactiveAdapterRegistry();
+	private ReactiveAdapterRegistry reactiveAdapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 
 
 	public InvocableHandlerMethod(HandlerMethod handlerMethod) {

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

@@ -81,7 +81,7 @@ public abstract class AbstractMessageReaderArgumentResolver extends HandlerMetho
 	 * @param readers readers to convert from the request body
 	 */
 	protected AbstractMessageReaderArgumentResolver(List<HttpMessageReader<?>> readers) {
-		this(readers, new ReactiveAdapterRegistry());
+		this(readers, ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 	/**

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

@@ -60,7 +60,7 @@ public abstract class AbstractMessageWriterResultHandler extends HandlerResultHa
 	protected AbstractMessageWriterResultHandler(List<HttpMessageWriter<?>> messageWriters,
 			RequestedContentTypeResolver contentTypeResolver) {
 
-		this(messageWriters, contentTypeResolver, new ReactiveAdapterRegistry());
+		this(messageWriters, contentTypeResolver, ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 	/**

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

@@ -163,7 +163,7 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, Application
 			this.argumentResolverConfigurer = new ArgumentResolverConfigurer();
 		}
 		if (this.reactiveAdapterRegistry == null) {
-			this.reactiveAdapterRegistry = new ReactiveAdapterRegistry();
+			this.reactiveAdapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		}
 
 		this.methodResolver = new ControllerMethodResolver(this.argumentResolverConfigurer,

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

@@ -56,7 +56,7 @@ public class ResponseBodyResultHandler extends AbstractMessageWriterResultHandle
 	public ResponseBodyResultHandler(List<HttpMessageWriter<?>> writers,
 			RequestedContentTypeResolver resolver) {
 
-		this(writers, resolver, new ReactiveAdapterRegistry());
+		this(writers, resolver, ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 	/**

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

@@ -63,7 +63,7 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 	public ResponseEntityResultHandler(List<HttpMessageWriter<?>> writers,
 			RequestedContentTypeResolver resolver) {
 
-		this(writers, resolver, new ReactiveAdapterRegistry());
+		this(writers, resolver, ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 	/**

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

@@ -70,7 +70,7 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 
 
 	public AbstractView() {
-		this(new ReactiveAdapterRegistry());
+		this(ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 	public AbstractView(ReactiveAdapterRegistry registry) {

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

@@ -101,7 +101,7 @@ public class ViewResolutionResultHandler extends HandlerResultHandlerSupport
 	public ViewResolutionResultHandler(List<ViewResolver> viewResolvers,
 			RequestedContentTypeResolver contentTypeResolver) {
 
-		this(viewResolvers, contentTypeResolver, new ReactiveAdapterRegistry());
+		this(viewResolvers, contentTypeResolver, ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 	/**

spring-webflux/src/test/java/org/springframework/web/reactive/result/HandlerResultHandlerTests.java

@@ -110,7 +110,7 @@ public class HandlerResultHandlerTests {
 		}
 
 		public TestResultHandler(RequestedContentTypeResolver contentTypeResolver) {
-			super(contentTypeResolver, new ReactiveAdapterRegistry());
+			super(contentTypeResolver, ReactiveAdapterRegistry.getSharedInstance());
 		}
 	}
 

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

@@ -76,7 +76,7 @@ public class ControllerMethodResolverTests {
 		applicationContext.refresh();
 
 		this.methodResolver = new ControllerMethodResolver(
-				resolvers, codecs.getReaders(), new ReactiveAdapterRegistry(), applicationContext);
+				resolvers, codecs.getReaders(), ReactiveAdapterRegistry.getSharedInstance(), applicationContext);
 
 		Method method = ResolvableMethod.on(TestController.class).mockCall(TestController::handle).method();
 		this.handlerMethod = new HandlerMethod(new TestController(), method);

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

@@ -62,7 +62,7 @@ public class CookieValueMethodArgumentResolverTests {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 		context.refresh();
 
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		this.resolver = new CookieValueMethodArgumentResolver(context.getBeanFactory(), adapterRegistry);
 		this.bindingContext = new BindingContext();
 

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

@@ -47,7 +47,7 @@ import static org.junit.Assert.assertTrue;
 public class ErrorsMethodArgumentResolverTests {
 
 	private final ErrorsMethodArgumentResolver resolver =
-			new ErrorsMethodArgumentResolver(new ReactiveAdapterRegistry());
+			new ErrorsMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 	private final BindingContext bindingContext = new BindingContext();
 

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

@@ -56,7 +56,7 @@ public class ExpressionValueMethodArgumentResolverTests {
 	public void setup() throws Exception {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 		context.refresh();
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		this.resolver = new ExpressionValueMethodArgumentResolver(context.getBeanFactory(), adapterRegistry);
 
 		Method method = ReflectionUtils.findMethod(getClass(), "params", (Class<?>[]) null);

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

@@ -75,7 +75,7 @@ public class HttpEntityArgumentResolverTests {
 	private HttpEntityArgumentResolver createResolver() {
 		List<HttpMessageReader<?>> readers = new ArrayList<>();
 		readers.add(new DecoderHttpMessageReader<>(StringDecoder.allMimeTypes(true)));
-		return new HttpEntityArgumentResolver(readers, new ReactiveAdapterRegistry());
+		return new HttpEntityArgumentResolver(readers, ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 

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

@@ -114,7 +114,7 @@ public class InitBinderBindingContextTests {
 	public void createBinderTypeConversion() throws Exception {
 		MockServerHttpRequest request = MockServerHttpRequest.get("/path?requestParam=22").build();
 		MockServerWebExchange exchange = MockServerWebExchange.from(request);
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		this.argumentResolvers.add(new RequestParamMethodArgumentResolver(null, adapterRegistry, false));
 
 		BindingContext context = createBindingContext("initBinderTypeConversion", WebDataBinder.class, int.class);

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

@@ -48,7 +48,7 @@ import static org.springframework.web.method.MvcAnnotationPredicates.matrixAttri
 public class MatrixVariablesMapMethodArgumentResolverTests {
 
 	private final MatrixVariableMapMethodArgumentResolver resolver =
-			new MatrixVariableMapMethodArgumentResolver(new ReactiveAdapterRegistry());
+			new MatrixVariableMapMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 	private final MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 

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

@@ -49,7 +49,7 @@ import static org.springframework.web.method.MvcAnnotationPredicates.matrixAttri
 public class MatrixVariablesMethodArgumentResolverTests {
 
 	private MatrixVariableMethodArgumentResolver resolver =
-			new MatrixVariableMethodArgumentResolver(null, new ReactiveAdapterRegistry());
+			new MatrixVariableMethodArgumentResolver(null, ReactiveAdapterRegistry.getSharedInstance());
 
 	private final MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 

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

@@ -40,7 +40,8 @@ import static org.springframework.mock.http.server.reactive.test.MockServerHttpR
  */
 public class ModelArgumentResolverTests {
 
-	private final ModelArgumentResolver resolver = new ModelArgumentResolver(new ReactiveAdapterRegistry());
+	private final ModelArgumentResolver resolver =
+			new ModelArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 	private final ServerWebExchange exchange = MockServerWebExchange.from(get("/"));
 

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

@@ -75,7 +75,7 @@ public class ModelAttributeMethodArgumentResolverTests {
 	@Test
 	public void supports() throws Exception {
 		ModelAttributeMethodArgumentResolver resolver =
-				new ModelAttributeMethodArgumentResolver(new ReactiveAdapterRegistry(), false);
+				new ModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance(), false);
 
 		MethodParameter param = this.testMethod.annotPresent(ModelAttribute.class).arg(Foo.class);
 		assertTrue(resolver.supportsParameter(param));
@@ -93,7 +93,7 @@ public class ModelAttributeMethodArgumentResolverTests {
 	@Test
 	public void supportsWithDefaultResolution() throws Exception {
 		ModelAttributeMethodArgumentResolver resolver =
-				new ModelAttributeMethodArgumentResolver(new ReactiveAdapterRegistry(), true);
+				new ModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance(), true);
 
 		MethodParameter param = this.testMethod.annotNotPresent(ModelAttribute.class).arg(Foo.class);
 		assertTrue(resolver.supportsParameter(param));
@@ -306,7 +306,7 @@ public class ModelAttributeMethodArgumentResolverTests {
 
 
 	private ModelAttributeMethodArgumentResolver createResolver() {
-		return new ModelAttributeMethodArgumentResolver(new ReactiveAdapterRegistry(), false);
+		return new ModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance(), false);
 	}
 
 	private ServerWebExchange postForm(String formData) throws URISyntaxException {

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

@@ -73,7 +73,7 @@ public class ModelInitializerTests {
 	@Before
 	public void setUp() throws Exception {
 
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 
 		ArgumentResolverConfigurer resolverConfigurer = new ArgumentResolverConfigurer();
 		resolverConfigurer.addCustomResolver(new ModelArgumentResolver(adapterRegistry));

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

@@ -58,7 +58,7 @@ public class PathVariableMapMethodArgumentResolverTests {
 
 	@Before
 	public void setup() throws Exception {
-		this.resolver = new PathVariableMapMethodArgumentResolver(new ReactiveAdapterRegistry());
+		this.resolver = new PathVariableMapMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 		Method method = ReflectionUtils.findMethod(getClass(), "handle", (Class<?>[]) null);
 		this.paramMap = new MethodParameter(method, 0);

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

@@ -65,7 +65,7 @@ public class PathVariableMethodArgumentResolverTests {
 
 	@Before
 	public void setup() throws Exception {
-		this.resolver = new PathVariableMethodArgumentResolver(null, new ReactiveAdapterRegistry());
+		this.resolver = new PathVariableMethodArgumentResolver(null, ReactiveAdapterRegistry.getSharedInstance());
 
 		Method method = ReflectionUtils.findMethod(getClass(), "handle", (Class<?>[]) null);
 		paramNamedString = new SynthesizingMethodParameter(method, 0);

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

@@ -39,7 +39,7 @@ import static org.junit.Assert.assertTrue;
 public class PrincipalArgumentResolverTests {
 
 	private final PrincipalArgumentResolver resolver =
-			new PrincipalArgumentResolver(new ReactiveAdapterRegistry());
+			new PrincipalArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 	private ResolvableMethod testMethod = ResolvableMethod.on(getClass()).named("handle").build();
 

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

@@ -64,7 +64,7 @@ public class RequestAttributeMethodArgumentResolverTests {
 	public void setup() throws Exception {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 		context.refresh();
-		ReactiveAdapterRegistry registry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry registry = ReactiveAdapterRegistry.getSharedInstance();
 		this.resolver = new RequestAttributeMethodArgumentResolver(context.getBeanFactory(), registry);
 	}
 

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

@@ -70,7 +70,7 @@ public class RequestBodyArgumentResolverTests {
 	public void setup() {
 		List<HttpMessageReader<?>> readers = new ArrayList<>();
 		readers.add(new DecoderHttpMessageReader<>(StringDecoder.allMimeTypes(true)));
-		this.resolver = new RequestBodyArgumentResolver(readers, new ReactiveAdapterRegistry());
+		this.resolver = new RequestBodyArgumentResolver(readers, ReactiveAdapterRegistry.getSharedInstance());
 	}
 
 

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

@@ -58,7 +58,7 @@ public class RequestHeaderMapMethodArgumentResolverTests {
 
 	@Before
 	public void setup() throws Exception {
-		resolver = new RequestHeaderMapMethodArgumentResolver(new ReactiveAdapterRegistry());
+		resolver = new RequestHeaderMapMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 		Method method = ReflectionUtils.findMethod(getClass(), "params", (Class<?>[]) null);
 		paramMap = new SynthesizingMethodParameter(method, 0);

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

@@ -73,7 +73,7 @@ public class RequestHeaderMethodArgumentResolverTests {
 	public void setup() throws Exception {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 		context.refresh();
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		this.resolver = new RequestHeaderMethodArgumentResolver(context.getBeanFactory(), adapterRegistry);
 
 		ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();

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

@@ -46,7 +46,7 @@ import static org.springframework.web.method.MvcAnnotationPredicates.requestPara
 public class RequestParamMapMethodArgumentResolverTests {
 
 	private final RequestParamMapMethodArgumentResolver resolver =
-			new RequestParamMapMethodArgumentResolver(new ReactiveAdapterRegistry());
+			new RequestParamMapMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 	private ResolvableMethod testMethod = ResolvableMethod.on(getClass()).named("handle").build();
 

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

@@ -63,7 +63,7 @@ public class RequestParamMethodArgumentResolverTests {
 	@Before
 	public void setup() throws Exception {
 
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		this.resolver = new RequestParamMethodArgumentResolver(null, adapterRegistry, true);
 
 		ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
@@ -100,7 +100,7 @@ public class RequestParamMethodArgumentResolverTests {
 
 	@Test
 	public void doesNotSupportParameterWithDefaultResolutionTurnedOff() {
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		this.resolver = new RequestParamMethodArgumentResolver(null, adapterRegistry, false);
 
 		MethodParameter param = this.testMethod.annotNotPresent(RequestParam.class).arg(String.class);

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

@@ -50,7 +50,7 @@ import static org.junit.Assert.fail;
 public class ServerWebExchangeArgumentResolverTests {
 
 	private final ServerWebExchangeArgumentResolver resolver =
-			new ServerWebExchangeArgumentResolver(new ReactiveAdapterRegistry());
+			new ServerWebExchangeArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 	private final MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/path"));
 

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

@@ -75,7 +75,7 @@ public class SessionAttributeMethodArgumentResolverTests {
 	public void setup() throws Exception {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 		context.refresh();
-		ReactiveAdapterRegistry adapterRegistry = new ReactiveAdapterRegistry();
+		ReactiveAdapterRegistry adapterRegistry = ReactiveAdapterRegistry.getSharedInstance();
 		this.resolver = new SessionAttributeMethodArgumentResolver(context.getBeanFactory(), adapterRegistry);
 
 		this.session = mock(WebSession.class);

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

@@ -44,7 +44,7 @@ import static org.mockito.Mockito.mock;
 public class WebSessionArgumentResolverTests {
 
 	private final WebSessionArgumentResolver resolver =
-			new WebSessionArgumentResolver(new ReactiveAdapterRegistry());
+			new WebSessionArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
 	private ResolvableMethod testMethod = ResolvableMethod.on(getClass()).named("handle").build();
 

spring-webflux/src/test/kotlin/org/springframework/web/reactive/result/method/annotation/RequestParamMethodArgumentResolverKotlinTests.kt

@@ -49,7 +49,7 @@ class RequestParamMethodArgumentResolverKotlinTests {
 
 	@Before
 	fun setup() {
-		this.resolver = RequestParamMethodArgumentResolver(null, ReactiveAdapterRegistry(), true)
+		this.resolver = RequestParamMethodArgumentResolver(null, ReactiveAdapterRegistry.getSharedInstance(), true)
 		val initializer = ConfigurableWebBindingInitializer()
 		initializer.conversionService = DefaultFormattingConversionService()
 		bindingContext = BindingContext(initializer)

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

@@ -83,7 +83,7 @@ class ReactiveTypeHandler {
 
 
 	public ReactiveTypeHandler() {
-		this(new ReactiveAdapterRegistry(), new SyncTaskExecutor(), new ContentNegotiationManager());
+		this(ReactiveAdapterRegistry.getSharedInstance(), new SyncTaskExecutor(), new ContentNegotiationManager());
 	}
 
 	ReactiveTypeHandler(ReactiveAdapterRegistry registry, TaskExecutor executor,

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

@@ -152,7 +152,7 @@ public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
 
 	private DeferredResultProcessingInterceptor[] deferredResultInterceptors = new DeferredResultProcessingInterceptor[0];
 
-	private ReactiveAdapterRegistry reactiveRegistry = new ReactiveAdapterRegistry();
+	private ReactiveAdapterRegistry reactiveRegistry = ReactiveAdapterRegistry.getSharedInstance();
 
 	private boolean ignoreDefaultModelOnRedirect = false;
 

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ReactiveTypeHandlerTests.java

@@ -80,7 +80,7 @@ public class ReactiveTypeHandlerTests {
 		ContentNegotiationManagerFactoryBean factoryBean = new ContentNegotiationManagerFactoryBean();
 		factoryBean.afterPropertiesSet();
 		ContentNegotiationManager manager = factoryBean.getObject();
-		this.handler = new ReactiveTypeHandler(new ReactiveAdapterRegistry(), new SyncTaskExecutor(), manager);
+		this.handler = new ReactiveTypeHandler(ReactiveAdapterRegistry.getSharedInstance(), new SyncTaskExecutor(), manager);
 		resetRequest();
 	}