Support for Map method argument in WebFlux

Issue: SPR-16086

Author: rstoyanchev

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

@@ -16,6 +16,8 @@
 
 package org.springframework.web.reactive.result.method.annotation;
 
+import java.util.Map;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.ui.Model;
@@ -26,7 +28,8 @@
 import org.springframework.web.server.ServerWebExchange;
 
 /**
- * Resolver for the {@link Model} controller method argument.
+ * Resolver for a controller method argument of type {@link Model} that can
+ * also be resolved as a {@link java.util.Map}.
  *
  * @author Rossen Stoyanchev
  * @since 5.0
@@ -41,15 +44,25 @@ public ModelArgumentResolver(ReactiveAdapterRegistry adapterRegistry) {
 
 	@Override
 	public boolean supportsParameter(MethodParameter parameter) {
-		return checkParameterTypeNoReactiveWrapper(parameter, Model.class::isAssignableFrom);
+		return checkParameterTypeNoReactiveWrapper(parameter,
+				type -> Model.class.isAssignableFrom(type) || Map.class.isAssignableFrom(type));
 	}
 
 	@Override
-	public Object resolveArgumentValue(MethodParameter methodParameter, BindingContext context,
+	public Object resolveArgumentValue(MethodParameter parameter, BindingContext context,
 			ServerWebExchange exchange) {
 
-		Assert.isAssignable(Model.class, methodParameter.getParameterType());
-		return context.getModel();
+		Class<?> type = parameter.getParameterType();
+		if (Model.class.isAssignableFrom(type)) {
+			return context.getModel();
+		}
+		else if (Map.class.isAssignableFrom(type)) {
+			return context.getModel().asMap();
+		}
+		else {
+			// Should never happen..
+			throw new IllegalStateException("Unexpected method parameter type: " + type);
+		}
 	}
 
 }

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

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2002-2017 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.time.Duration;
+import java.util.Map;
+
+import org.junit.Test;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.core.ReactiveAdapterRegistry;
+import org.springframework.mock.web.test.server.MockServerWebExchange;
+import org.springframework.ui.Model;
+import org.springframework.ui.ModelMap;
+import org.springframework.web.method.ResolvableMethod;
+import org.springframework.web.reactive.BindingContext;
+import org.springframework.web.server.ServerWebExchange;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.springframework.mock.http.server.reactive.test.MockServerHttpRequest.get;
+
+/**
+ * Unit tests for {@link ModelArgumentResolver}.
+ * @author Rossen Stoyanchev
+ */
+public class ModelArgumentResolverTests {
+
+	private final ModelArgumentResolver resolver = new ModelArgumentResolver(new ReactiveAdapterRegistry());
+
+	private final ServerWebExchange exchange = MockServerWebExchange.from(get("/"));
+
+	private final ResolvableMethod testMethod = ResolvableMethod.on(getClass()).named("handle").build();
+
+
+	@Test
+	public void supportsParameter() throws Exception {
+		assertTrue(this.resolver.supportsParameter(this.testMethod.arg(Model.class)));
+		assertTrue(this.resolver.supportsParameter(this.testMethod.arg(Map.class, String.class, Object.class)));
+		assertTrue(this.resolver.supportsParameter(this.testMethod.arg(ModelMap.class)));
+		assertFalse(this.resolver.supportsParameter(this.testMethod.arg(Object.class)));
+	}
+
+	@Test
+	public void resolveArgument() throws Exception {
+		testResolveArgument(this.testMethod.arg(Model.class));
+		testResolveArgument(this.testMethod.arg(Map.class, String.class, Object.class));
+		testResolveArgument(this.testMethod.arg(ModelMap.class));
+	}
+
+	private void testResolveArgument(MethodParameter parameter) {
+		BindingContext context = new BindingContext();
+		Object result = this.resolver.resolveArgument(parameter, context, this.exchange).block(Duration.ZERO);
+		assertSame(context.getModel(), result);
+	}
+
+	@SuppressWarnings("unused")
+	void handle(Model model, Map<String, Object> map, ModelMap modelMap, Object object) {}
+
+}