Reactive support for @ModelAttribute methods

Issue: SPR-14542

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

@@ -0,0 +1,169 @@
+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.web.reactive.result.method.annotation;
+
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import reactor.core.publisher.Mono;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.core.ReactiveAdapter;
+import org.springframework.core.ReactiveAdapterRegistry;
+import org.springframework.core.ResolvableType;
+import org.springframework.core.annotation.AnnotatedElementUtils;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.StringUtils;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.support.WebBindingInitializer;
+import org.springframework.web.method.HandlerMethod;
+import org.springframework.web.reactive.HandlerResult;
+import org.springframework.web.reactive.result.method.BindingContext;
+import org.springframework.web.reactive.result.method.HandlerMethodArgumentResolver;
+import org.springframework.web.reactive.result.method.InvocableHandlerMethod;
+import org.springframework.web.reactive.result.method.SyncHandlerMethodArgumentResolver;
+import org.springframework.web.reactive.result.method.SyncInvocableHandlerMethod;
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ * A helper class for {@link RequestMappingHandlerAdapter} that assists with
+ * creating a {@code BindingContext} and initialize it, and its model, through
+ * {@code @InitBinder} and {@code @ModelAttribute} methods.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.0
+ */
+class BindingContextFactory {
+
+	private final RequestMappingHandlerAdapter adapter;
+
+
+	public BindingContextFactory(RequestMappingHandlerAdapter adapter) {
+		this.adapter = adapter;
+	}
+
+
+	public RequestMappingHandlerAdapter getAdapter() {
+		return this.adapter;
+	}
+
+	private WebBindingInitializer getBindingInitializer() {
+		return getAdapter().getWebBindingInitializer();
+	}
+
+	private List<SyncHandlerMethodArgumentResolver> getInitBinderArgumentResolvers() {
+		return getAdapter().getInitBinderArgumentResolvers();
+	}
+
+	private List<HandlerMethodArgumentResolver> getArgumentResolvers() {
+		return getAdapter().getArgumentResolvers();
+	}
+
+	private ReactiveAdapterRegistry getAdapterRegistry() {
+		return getAdapter().getReactiveAdapterRegistry();
+	}
+
+	private Stream<Method> getInitBinderMethods(HandlerMethod handlerMethod) {
+		return getAdapter().getInitBinderMethods(handlerMethod.getBeanType()).stream();
+	}
+
+	private Stream<Method> getModelAttributeMethods(HandlerMethod handlerMethod) {
+		return getAdapter().getModelAttributeMethods(handlerMethod.getBeanType()).stream();
+	}
+
+
+	/**
+	 * Create and initialize a BindingContext for the current request.
+	 * @param handlerMethod the request handling method
+	 * @param exchange the current exchange
+	 * @return Mono with the BindingContext instance
+	 */
+	public Mono<BindingContext> createBindingContext(HandlerMethod handlerMethod,
+			ServerWebExchange exchange) {
+
+		List<SyncInvocableHandlerMethod> invocableMethods = getInitBinderMethods(handlerMethod)
+				.map(method -> {
+					Object bean = handlerMethod.getBean();
+					SyncInvocableHandlerMethod invocable = new SyncInvocableHandlerMethod(bean, method);
+					invocable.setSyncArgumentResolvers(getInitBinderArgumentResolvers());
+					return invocable;
+				})
+				.collect(Collectors.toList());
+
+		BindingContext bindingContext =
+				new InitBinderBindingContext(getBindingInitializer(), invocableMethods);
+
+		return initModel(handlerMethod, bindingContext, exchange).then(Mono.just(bindingContext));
+	}
+
+	@SuppressWarnings("Convert2MethodRef")
+	private Mono<Void> initModel(HandlerMethod handlerMethod, BindingContext context,
+			ServerWebExchange exchange) {
+
+		List<Mono<HandlerResult>> resultMonos = getModelAttributeMethods(handlerMethod)
+				.map(method -> {
+					Object bean = handlerMethod.getBean();
+					InvocableHandlerMethod invocable = new InvocableHandlerMethod(bean, method);
+					invocable.setArgumentResolvers(getArgumentResolvers());
+					return invocable;
+				})
+				.map(invocable -> invocable.invoke(exchange, context))
+				.collect(Collectors.toList());
+
+		return Mono
+				.when(resultMonos, resultArr -> processModelMethodMonos(resultArr, context))
+				.then(voidMonos -> Mono.when(voidMonos));
+	}
+
+	private List<Mono<Void>> processModelMethodMonos(Object[] resultArr, BindingContext context) {
+		return Arrays.stream(resultArr)
+				.map(result -> processModelMethodResult((HandlerResult) result, context))
+				.collect(Collectors.toList());
+	}
+
+	private Mono<Void> processModelMethodResult(HandlerResult result, BindingContext context) {
+		Object value = result.getReturnValue().orElse(null);
+		if (value == null) {
+			return Mono.empty();
+		}
+
+		ResolvableType type = result.getReturnType();
+		ReactiveAdapter adapter = getAdapterRegistry().getAdapterFrom(type.getRawClass(), value);
+		Class<?> valueType = (adapter != null ? type.resolveGeneric(0) : type.resolve());
+
+		if (Void.class.equals(valueType) || void.class.equals(valueType)) {
+			return (adapter != null ? adapter.toMono(value) : Mono.empty());
+		}
+
+		String name = getAttributeName(valueType, result.getReturnTypeSource());
+		context.getModel().asMap().putIfAbsent(name, value);
+		return Mono.empty();
+	}
+
+	private String getAttributeName(Class<?> valueType, MethodParameter parameter) {
+		Method method = parameter.getMethod();
+		ModelAttribute annot = AnnotatedElementUtils.findMergedAnnotation(method, ModelAttribute.class);
+		if (annot != null && StringUtils.hasText(annot.value())) {
+			return annot.value();
+		}
+		// TODO: Conventions does not deal with async wrappers
+		return ClassUtils.getShortNameAsProperty(valueType);
+	}
+
+}

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

@@ -60,20 +60,28 @@ import org.springframework.web.server.ServerWebExchange;
  */
 public class ModelAttributeMethodArgumentResolver implements HandlerMethodArgumentResolver {
 
-	private final boolean useDefaultResolution;
-
 	private final ReactiveAdapterRegistry adapterRegistry;
 
+	private final boolean useDefaultResolution;
+
 
 	/**
 	 * Class constructor.
+	 * @param registry for adapting to other reactive types from and to Mono
+	 */
+	public ModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry registry) {
+		this(registry, false);
+	}
+
+	/**
+	 * Class constructor with a default resolution mode flag.
+	 * @param registry for adapting to other reactive types from and to Mono
 	 * @param useDefaultResolution if "true", non-simple method arguments and
 	 * return values are considered model attributes with or without a
 	 * {@code @ModelAttribute} annotation present.
-	 * @param registry for adapting to other reactive types from and to Mono
 	 */
-	public ModelAttributeMethodArgumentResolver(boolean useDefaultResolution,
-			ReactiveAdapterRegistry registry) {
+	public ModelAttributeMethodArgumentResolver(ReactiveAdapterRegistry registry,
+			boolean useDefaultResolution) {
 
 		Assert.notNull(registry, "'ReactiveAdapterRegistry' is required.");
 		this.useDefaultResolution = useDefaultResolution;

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

@@ -42,6 +42,8 @@ import org.springframework.http.codec.DecoderHttpMessageReader;
 import org.springframework.http.codec.HttpMessageReader;
 import org.springframework.util.ReflectionUtils;
 import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.support.WebBindingInitializer;
 import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.method.annotation.ExceptionHandlerMethodResolver;
@@ -51,7 +53,6 @@ import org.springframework.web.reactive.result.method.BindingContext;
 import org.springframework.web.reactive.result.method.HandlerMethodArgumentResolver;
 import org.springframework.web.reactive.result.method.InvocableHandlerMethod;
 import org.springframework.web.reactive.result.method.SyncHandlerMethodArgumentResolver;
-import org.springframework.web.reactive.result.method.SyncInvocableHandlerMethod;
 import org.springframework.web.server.ServerWebExchange;
 
 /**
@@ -82,8 +83,12 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, BeanFactory
 	private ConfigurableBeanFactory beanFactory;
 
 
+	private final BindingContextFactory bindingContextFactory = new BindingContextFactory(this);
+
 	private final Map<Class<?>, Set<Method>> initBinderCache = new ConcurrentHashMap<>(64);
 
+	private final Map<Class<?>, Set<Method>> modelAttributeCache = new ConcurrentHashMap<>(64);
+
 	private final Map<Class<?>, ExceptionHandlerMethodResolver> exceptionHandlerCache =
 			new ConcurrentHashMap<>(64);
 
@@ -225,11 +230,12 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, BeanFactory
 		List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();
 
 		// Annotation-based argument resolution
-		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
+		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory()));
 		resolvers.add(new RequestParamMapMethodArgumentResolver());
 		resolvers.add(new PathVariableMethodArgumentResolver(getBeanFactory()));
 		resolvers.add(new PathVariableMapMethodArgumentResolver());
 		resolvers.add(new RequestBodyArgumentResolver(getMessageReaders(), getReactiveAdapterRegistry()));
+		resolvers.add(new ModelAttributeMethodArgumentResolver(getReactiveAdapterRegistry()));
 		resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));
 		resolvers.add(new RequestHeaderMapMethodArgumentResolver());
 		resolvers.add(new CookieValueMethodArgumentResolver(getBeanFactory()));
@@ -240,6 +246,7 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, BeanFactory
 		// Type-based argument resolution
 		resolvers.add(new HttpEntityArgumentResolver(getMessageReaders(), getReactiveAdapterRegistry()));
 		resolvers.add(new ModelArgumentResolver());
+		resolvers.add(new ErrorsMethodArgumentResolver(getReactiveAdapterRegistry()));
 		resolvers.add(new ServerWebExchangeArgumentResolver());
 		resolvers.add(new PrincipalArgumentResolver());
 		resolvers.add(new WebSessionArgumentResolver());
@@ -251,6 +258,7 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, BeanFactory
 
 		// Catch-all
 		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
+		resolvers.add(new ModelAttributeMethodArgumentResolver(getReactiveAdapterRegistry(), true));
 		return resolvers;
 	}
 
@@ -290,34 +298,31 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, BeanFactory
 
 	@Override
 	public Mono<HandlerResult> handle(ServerWebExchange exchange, Object handler) {
+
 		HandlerMethod handlerMethod = (HandlerMethod) handler;
 		InvocableHandlerMethod invocable = new InvocableHandlerMethod(handlerMethod);
 		invocable.setArgumentResolvers(getArgumentResolvers());
-		BindingContext bindingContext = getBindingContext(handlerMethod);
-		return invocable.invoke(exchange, bindingContext)
-				.map(result -> result.setExceptionHandler(
-						ex -> handleException(ex, handlerMethod, bindingContext, exchange)))
-				.otherwise(ex -> handleException(
-						ex, handlerMethod, bindingContext, exchange));
+
+		Mono<BindingContext> bindingContextMono =
+				this.bindingContextFactory.createBindingContext(handlerMethod, exchange);
+
+		return bindingContextMono.then(bindingContext ->
+				invocable.invoke(exchange, bindingContext)
+						.doOnNext(result -> result.setExceptionHandler(
+								ex -> handleException(ex, handlerMethod, bindingContext, exchange)))
+						.otherwise(ex -> handleException(
+								ex, handlerMethod, bindingContext, exchange)));
 	}
 
-	private BindingContext getBindingContext(HandlerMethod handlerMethod) {
-		Class<?> handlerType = handlerMethod.getBeanType();
-		Set<Method> methods = this.initBinderCache.get(handlerType);
-		if (methods == null) {
-			methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS);
-			this.initBinderCache.put(handlerType, methods);
-		}
-		List<SyncInvocableHandlerMethod> initBinderMethods = new ArrayList<>();
-		for (Method method : methods) {
-			Object bean = handlerMethod.getBean();
-			SyncInvocableHandlerMethod initBinderMethod = new SyncInvocableHandlerMethod(bean, method);
-			initBinderMethod.setSyncArgumentResolvers(getInitBinderArgumentResolvers());
-			initBinderMethods.add(initBinderMethod);
-		}
-		return new InitBinderBindingContext(getWebBindingInitializer(), initBinderMethods);
+	Set<Method> getInitBinderMethods(Class<?> handlerType) {
+		return this.initBinderCache.computeIfAbsent(handlerType, aClass ->
+				MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS));
 	}
 
+	Set<Method> getModelAttributeMethods(Class<?> handlerType) {
+		return this.modelAttributeCache.computeIfAbsent(handlerType, aClass ->
+				MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS));
+	}
 
 	private Mono<HandlerResult> handleException(Throwable ex, HandlerMethod handlerMethod,
 			BindingContext bindingContext, ServerWebExchange exchange) {
@@ -360,7 +365,14 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, BeanFactory
 	/**
 	 * MethodFilter that matches {@link InitBinder @InitBinder} methods.
 	 */
-	public static final ReflectionUtils.MethodFilter INIT_BINDER_METHODS =
-			method -> AnnotationUtils.findAnnotation(method, InitBinder.class) != null;
+	public static final ReflectionUtils.MethodFilter INIT_BINDER_METHODS = method ->
+			AnnotationUtils.findAnnotation(method, InitBinder.class) != null;
+
+	/**
+	 * MethodFilter that matches {@link ModelAttribute @ModelAttribute} methods.
+	 */
+	public static final ReflectionUtils.MethodFilter MODEL_ATTRIBUTE_METHODS = method ->
+			(AnnotationUtils.findAnnotation(method, RequestMapping.class) == null) &&
+					(AnnotationUtils.findAnnotation(method, ModelAttribute.class) != null);
 
 }

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

@@ -20,8 +20,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 
-import reactor.core.publisher.Mono;
-
 import org.springframework.beans.BeanUtils;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.core.MethodParameter;
@@ -57,6 +55,17 @@ public class RequestParamMethodArgumentResolver extends AbstractNamedValueSyncAr
 
 
 	/**
+	 * Class constructor.
+	 * @param beanFactory a bean factory used for resolving  ${...} placeholder
+	 * and #{...} SpEL expressions in default values, or {@code null} if default
+	 * values are not expected to contain expressions
+	 */
+	public RequestParamMethodArgumentResolver(ConfigurableBeanFactory beanFactory) {
+		this(beanFactory, false);
+	}
+
+	/**
+	 * Class constructor with a default resolution mode flag.
 	 * @param beanFactory a bean factory used for resolving  ${...} placeholder
 	 * and #{...} SpEL expressions in default values, or {@code null} if default
 	 * values are not expected to contain expressions
@@ -65,7 +74,9 @@ public class RequestParamMethodArgumentResolver extends AbstractNamedValueSyncAr
 	 * is treated as a request parameter even if it isn't annotated, the
 	 * request parameter name is derived from the method parameter name.
 	 */
-	public RequestParamMethodArgumentResolver(ConfigurableBeanFactory beanFactory, boolean useDefaultResolution) {
+	public RequestParamMethodArgumentResolver(ConfigurableBeanFactory beanFactory,
+			boolean useDefaultResolution) {
+
 		super(beanFactory);
 		this.useDefaultResolution = useDefaultResolution;
 	}

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

@@ -191,15 +191,11 @@ public class ViewResolutionResultHandler extends AbstractHandlerResultHandler
 		ReactiveAdapter adapter = getAdapterRegistry().getAdapterFrom(parameterType.getRawClass(), optional);
 
 		if (adapter != null) {
-			if (optional.isPresent()) {
-				Mono<?> converted = adapter.toMono(optional);
-				returnValueMono = converted.map(o -> o);
-			}
-			else {
-				returnValueMono = Mono.empty();
-			}
-			elementType = adapter.getDescriptor().isNoValue() ?
-					ResolvableType.forClass(Void.class) : parameterType.getGeneric(0);
+			returnValueMono = optional
+					.map(value -> adapter.toMono(value).cast(Object.class))
+					.orElse(Mono.empty());
+			elementType = !adapter.getDescriptor().isNoValue() ?
+					parameterType.getGeneric(0) : ResolvableType.forClass(Void.class);
 		}
 		else {
 			returnValueMono = Mono.justOrEmpty(result.getReturnValue());

spring-web-reactive/src/test/java/org/springframework/web/reactive/DispatcherHandlerErrorTests.java

@@ -108,28 +108,13 @@ public class DispatcherHandlerErrorTests {
 				.verify();
 	}
 
-	@Test
-	public void unknownMethodArgumentType() throws Exception {
-		this.request.setUri("/unknown-argument-type");
-		Mono<Void> publisher = this.dispatcherHandler.handle(this.exchange);
-
-		StepVerifier.create(publisher)
-				.consumeErrorWith(error -> {
-					assertThat(error, instanceOf(IllegalStateException.class));
-					assertThat(error.getMessage(), startsWith("No resolver for argument [0]"));
-				})
-				.verify();
-	}
-
 	@Test
 	public void controllerReturnsMonoError() throws Exception {
 		this.request.setUri("/error-signal");
 		Mono<Void> publisher = this.dispatcherHandler.handle(this.exchange);
 
 		StepVerifier.create(publisher)
-				.consumeErrorWith(error -> {
-					assertSame(EXCEPTION, error);
-				})
+				.consumeErrorWith(error -> assertSame(EXCEPTION, error))
 				.verify();
 	}
 
@@ -138,10 +123,8 @@ public class DispatcherHandlerErrorTests {
 		this.request.setUri("/raise-exception");
 		Mono<Void> publisher = this.dispatcherHandler.handle(this.exchange);
 
-		StepVerifier.<Void>create(publisher)
-				.consumeErrorWith(error -> {
-					assertSame(EXCEPTION, error);
-				})
+		StepVerifier.create(publisher)
+				.consumeErrorWith(error -> assertSame(EXCEPTION, error))
 				.verify();
 	}
 
@@ -164,9 +147,7 @@ public class DispatcherHandlerErrorTests {
 		Mono<Void> publisher = this.dispatcherHandler.handle(this.exchange);
 
 		StepVerifier.create(publisher)
-				.consumeErrorWith(error -> {
-					assertThat(error, instanceOf(NotAcceptableStatusException.class));
-				})
+				.consumeErrorWith(error -> assertThat(error, instanceOf(NotAcceptableStatusException.class)))
 				.verify();
 	}
 
@@ -226,10 +207,6 @@ public class DispatcherHandlerErrorTests {
 	@SuppressWarnings("unused")
 	private static class TestController {
 
-		@RequestMapping("/unknown-argument-type")
-		public void unknownArgumentType(Foo arg) {
-		}
-
 		@RequestMapping("/error-signal")
 		@ResponseBody
 		public Publisher<String> errorSignal() {

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

@@ -0,0 +1,182 @@
+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.web.reactive.result.method.annotation;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+import rx.Single;
+
+import org.springframework.context.support.StaticApplicationContext;
+import org.springframework.http.HttpMethod;
+import org.springframework.mock.http.server.reactive.test.MockServerHttpRequest;
+import org.springframework.mock.http.server.reactive.test.MockServerHttpResponse;
+import org.springframework.ui.Model;
+import org.springframework.util.ObjectUtils;
+import org.springframework.validation.Validator;
+import org.springframework.web.bind.WebDataBinder;
+import org.springframework.web.bind.WebExchangeDataBinder;
+import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.method.HandlerMethod;
+import org.springframework.web.reactive.config.WebReactiveConfigurationSupport;
+import org.springframework.web.reactive.result.ResolvableMethod;
+import org.springframework.web.reactive.result.method.BindingContext;
+import org.springframework.web.server.ServerWebExchange;
+import org.springframework.web.server.adapter.DefaultServerWebExchange;
+import org.springframework.web.server.session.DefaultWebSessionManager;
+import org.springframework.web.server.session.WebSessionManager;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Unit tests for {@link BindingContextFactory}.
+ * @author Rossen Stoyanchev
+ */
+public class BindingContextFactoryTests {
+
+	private BindingContextFactory contextFactory;
+
+	private ServerWebExchange exchange;
+
+
+	@Before
+	public void setUp() throws Exception {
+		WebReactiveConfigurationSupport configurationSupport = new WebReactiveConfigurationSupport();
+		configurationSupport.setApplicationContext(new StaticApplicationContext());
+		RequestMappingHandlerAdapter adapter = configurationSupport.requestMappingHandlerAdapter();
+		adapter.afterPropertiesSet();
+		this.contextFactory = new BindingContextFactory(adapter);
+
+		MockServerHttpRequest request = new MockServerHttpRequest(HttpMethod.GET, "/path");
+		MockServerHttpResponse response = new MockServerHttpResponse();
+		WebSessionManager manager = new DefaultWebSessionManager();
+		this.exchange = new DefaultServerWebExchange(request, response, manager);
+	}
+
+
+	@SuppressWarnings("unchecked")
+	@Test
+	public void basic() throws Exception {
+
+		Validator validator = mock(Validator.class);
+		TestController controller = new TestController(validator);
+
+		HandlerMethod handlerMethod = ResolvableMethod.on(controller)
+				.annotated(RequestMapping.class)
+				.resolveHandlerMethod();
+
+		BindingContext bindingContext =
+				this.contextFactory.createBindingContext(handlerMethod, this.exchange)
+						.blockMillis(5000);
+
+		WebExchangeDataBinder binder = bindingContext.createDataBinder(this.exchange, "name");
+		assertEquals(Collections.singletonList(validator), binder.getValidators());
+
+		Map<String, Object> model = bindingContext.getModel().asMap();
+		assertEquals(5, model.size());
+
+		Object value = model.get("bean");
+		assertEquals("Bean", ((TestBean) value).getName());
+
+		value = model.get("monoBean");
+		assertEquals("Mono Bean", ((Mono<TestBean>) value).blockMillis(5000).getName());
+
+		value = model.get("singleBean");
+		assertEquals("Single Bean", ((Single<TestBean>) value).toBlocking().value().getName());
+
+		value = model.get("voidMethodBean");
+		assertEquals("Void Method Bean", ((TestBean) value).getName());
+
+		value = model.get("voidMonoMethodBean");
+		assertEquals("Void Mono Method Bean", ((TestBean) value).getName());
+	}
+
+
+	@SuppressWarnings("unused")
+	private static class TestController {
+
+		private Validator[] validators;
+
+
+		public TestController(Validator... validators) {
+			this.validators = validators;
+		}
+
+
+		@InitBinder
+		public void initDataBinder(WebDataBinder dataBinder) {
+			if (!ObjectUtils.isEmpty(this.validators)) {
+				dataBinder.addValidators(this.validators);
+			}
+		}
+
+		@ModelAttribute("bean")
+		public TestBean returnValue() {
+			return new TestBean("Bean");
+		}
+
+		@ModelAttribute("monoBean")
+		public Mono<TestBean> returnValueMono() {
+			return Mono.just(new TestBean("Mono Bean"));
+		}
+
+		@ModelAttribute("singleBean")
+		public Single<TestBean> returnValueSingle() {
+			return Single.just(new TestBean("Single Bean"));
+		}
+
+		@ModelAttribute
+		public void voidMethodBean(Model model) {
+			model.addAttribute("voidMethodBean", new TestBean("Void Method Bean"));
+		}
+
+		@ModelAttribute
+		public Mono<Void> voidMonoMethodBean(Model model) {
+			return Mono.just("Void Mono Method Bean")
+					.doOnNext(name -> model.addAttribute("voidMonoMethodBean", new TestBean(name)))
+					.then();
+		}
+
+		@RequestMapping
+		public void handle() {}
+	}
+
+	private static class TestBean {
+
+		private final String name;
+
+		TestBean(String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return this.name;
+		}
+
+		@Override
+		public String toString() {
+			return "TestBean[name=" + this.name + "]";
+		}
+	}
+
+}

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

@@ -91,7 +91,7 @@ public class ModelAttributeMethodArgumentResolverTests {
 	public void supports() throws Exception {
 
 		ModelAttributeMethodArgumentResolver resolver =
-				new ModelAttributeMethodArgumentResolver(false, new ReactiveAdapterRegistry());
+				new ModelAttributeMethodArgumentResolver(new ReactiveAdapterRegistry(), false);
 
 		ResolvableType type = forClass(Foo.class);
 		assertTrue(resolver.supportsParameter(parameter(type)));
@@ -110,7 +110,7 @@ public class ModelAttributeMethodArgumentResolverTests {
 	public void supportsWithDefaultResolution() throws Exception {
 
 		ModelAttributeMethodArgumentResolver resolver =
-				new ModelAttributeMethodArgumentResolver(true, new ReactiveAdapterRegistry());
+				new ModelAttributeMethodArgumentResolver(new ReactiveAdapterRegistry(), true);
 
 		ResolvableType type = forClass(Foo.class);
 		assertTrue(resolver.supportsParameter(parameterNotAnnotated(type)));
@@ -282,7 +282,7 @@ public class ModelAttributeMethodArgumentResolverTests {
 
 
 	private ModelAttributeMethodArgumentResolver createResolver() {
-		return new ModelAttributeMethodArgumentResolver(false, new ReactiveAdapterRegistry());
+		return new ModelAttributeMethodArgumentResolver(new ReactiveAdapterRegistry());
 	}
 
 	private MethodParameter parameter(ResolvableType type) {

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

@@ -18,8 +18,10 @@ package org.springframework.web.reactive.result.method.annotation;
 
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.Optional;
 
 import org.junit.Test;
+import reactor.core.publisher.Mono;
 
 import org.springframework.beans.propertyeditors.CustomDateEditor;
 import org.springframework.context.ApplicationContext;
@@ -27,12 +29,17 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.http.HttpHeaders;
-import org.springframework.stereotype.Controller;
+import org.springframework.http.MediaType;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
+import org.springframework.validation.Errors;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestParam;
-import org.springframework.web.bind.annotation.ResponseBody;
+import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.reactive.config.EnableWebReactive;
 
 import static org.junit.Assert.assertEquals;
@@ -62,6 +69,18 @@ public class RequestMappingDataBindingIntegrationTests extends AbstractRequestMa
 						new HttpHeaders(), null, String.class).getBody());
 	}
 
+	@Test
+	public void handleForm() throws Exception {
+
+		MultiValueMap<String, String> formData = new LinkedMultiValueMap<>();
+		formData.add("name", "George");
+		formData.add("age", "5");
+
+		assertEquals("Processed form: Foo[id=1, name='George', age=5]",
+				performPost("/foos/1", MediaType.APPLICATION_FORM_URLENCODED, formData,
+						MediaType.TEXT_PLAIN, String.class).getBody());
+	}
+
 
 	@Configuration
 	@EnableWebReactive
@@ -70,21 +89,73 @@ public class RequestMappingDataBindingIntegrationTests extends AbstractRequestMa
 	static class WebConfig {
 	}
 
-	@Controller
-	@SuppressWarnings("unused")
+	@RestController
+	@SuppressWarnings({"unused", "OptionalUsedAsFieldOrParameterType"})
 	private static class TestController {
 
 		@InitBinder
-		public void initBinder(WebDataBinder dataBinder, @RequestParam("date-pattern") String pattern) {
-			CustomDateEditor dateEditor = new CustomDateEditor(new SimpleDateFormat(pattern), false);
-			dataBinder.registerCustomEditor(Date.class, dateEditor);
+		public void initBinder(WebDataBinder binder,
+				@RequestParam("date-pattern") Optional<String> optionalPattern) {
+
+			optionalPattern.ifPresent(pattern -> {
+				CustomDateEditor dateEditor = new CustomDateEditor(new SimpleDateFormat(pattern), false);
+				binder.registerCustomEditor(Date.class, dateEditor);
+			});
 		}
 
 		@PostMapping("/date-param")
-		@ResponseBody
 		public String handleDateParam(@RequestParam Date date) {
 			return "Processed date!";
 		}
+
+		@ModelAttribute
+		public Mono<Foo> addFooAttribute(@PathVariable("id") Optional<Long> optiponalId) {
+			return optiponalId.map(id -> Mono.just(new Foo(id))).orElse(Mono.empty());
+		}
+
+		@PostMapping("/foos/{id}")
+		public String handleForm(@ModelAttribute Foo foo, Errors errors) {
+			return (errors.hasErrors() ?
+					"Form not processed" : "Processed form: " + foo);
+		}
+	}
+
+	private static class Foo {
+
+		private final Long id;
+
+		private String name;
+
+		private int age;
+
+		public Foo(Long id) {
+			this.id = id;
+		}
+
+		public Long getId() {
+			return id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public int getAge() {
+			return this.age;
+		}
+
+		public void setAge(int age) {
+			this.age = age;
+		}
+
+		@Override
+		public String toString() {
+			return "Foo[id=" + this.id + ", name='" + this.name + "', age=" + this.age + "]";
+		}
 	}
 
 }