Reactive support for Errors argument

Issue: SPR-14542

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

@@ -0,0 +1,118 @@
+/*
+ * 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 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.util.Assert;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.StringUtils;
+import org.springframework.validation.BindingResult;
+import org.springframework.validation.Errors;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.reactive.result.method.BindingContext;
+import org.springframework.web.reactive.result.method.HandlerMethodArgumentResolver;
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ * Resolve {@link Errors} or {@link BindingResult} method arguments.
+ * An {@code Errors} argument is expected to appear immediately after the
+ * model attribute in the method signature.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.0
+ */
+public class ErrorsMethodArgumentResolver implements HandlerMethodArgumentResolver {
+
+	private final ReactiveAdapterRegistry adapterRegistry;
+
+
+	/**
+	 * Class constructor.
+	 * @param registry for adapting to other reactive types from and to Mono
+	 */
+	public ErrorsMethodArgumentResolver(ReactiveAdapterRegistry registry) {
+		Assert.notNull(registry, "'ReactiveAdapterRegistry' is required.");
+		this.adapterRegistry = registry;
+	}
+
+
+	/**
+	 * Return the configured {@link ReactiveAdapterRegistry}.
+	 */
+	public ReactiveAdapterRegistry getAdapterRegistry() {
+		return this.adapterRegistry;
+	}
+
+
+	@Override
+	public boolean supportsParameter(MethodParameter parameter) {
+		Class<?> clazz = parameter.getParameterType();
+		return Errors.class.isAssignableFrom(clazz);
+	}
+
+
+	@Override
+	public Mono<Object> resolveArgument(MethodParameter parameter, BindingContext context,
+			ServerWebExchange exchange) {
+
+		String name = getModelAttributeName(parameter);
+		Object errors = context.getModel().asMap().get(BindingResult.MODEL_KEY_PREFIX + name);
+
+		Mono<?> errorsMono;
+		if (Mono.class.isAssignableFrom(errors.getClass())) {
+			errorsMono = (Mono<?>) errors;
+		}
+		else if (Errors.class.isAssignableFrom(errors.getClass())) {
+			errorsMono = Mono.just(errors);
+		}
+		else {
+			throw new IllegalStateException(
+					"Unexpected Errors/BindingResult type: " + errors.getClass().getName());
+		}
+
+		return errorsMono.cast(Object.class);
+	}
+
+	private String getModelAttributeName(MethodParameter parameter) {
+
+		Assert.isTrue(parameter.getParameterIndex() > 0,
+				"Errors argument must be immediately after a model attribute argument.");
+
+		int index = parameter.getParameterIndex() - 1;
+		MethodParameter attributeParam = new MethodParameter(parameter.getMethod(), index);
+		Class<?> attributeType = attributeParam.getParameterType();
+
+		ResolvableType type = ResolvableType.forMethodParameter(attributeParam);
+		ReactiveAdapter adapterTo = getAdapterRegistry().getAdapterTo(type.resolve());
+
+		Assert.isNull(adapterTo, "Errors/BindingResult cannot be used with an async model attribute. " +
+				"Either declare the model attribute without the async wrapper type " +
+				"or handle WebExchangeBindException through the async type.");
+
+		ModelAttribute annot = parameter.getParameterAnnotation(ModelAttribute.class);
+		if (annot != null && StringUtils.hasText(annot.value())) {
+			return annot.value();
+		}
+		// TODO: Conventions does not deal with async wrappers
+		return ClassUtils.getShortNameAsProperty(attributeType);
+	}
+
+}

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

@@ -152,10 +152,12 @@ public class ModelAttributeMethodArgumentResolver implements HandlerMethodArgume
 	}
 
 	private String getAttributeName(Class<?> valueType, MethodParameter parameter) {
-		ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class);
-		String name = (ann != null ? ann.value() : null);
+		ModelAttribute annot = parameter.getParameterAnnotation(ModelAttribute.class);
+		if (annot != null && StringUtils.hasText(annot.value())) {
+			return annot.value();
+		}
 		// TODO: Conventions does not deal with async wrappers
-		return StringUtils.hasText(name) ? name : ClassUtils.getShortNameAsProperty(valueType);
+		return ClassUtils.getShortNameAsProperty(valueType);
 	}
 
 	private Mono<?> getAttributeMono(String attributeName, Class<?> attributeType,

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

@@ -0,0 +1,161 @@
+/*
+ * 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 org.junit.Before;
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+import reactor.core.publisher.MonoProcessor;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.core.ReactiveAdapterRegistry;
+import org.springframework.core.ResolvableType;
+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.validation.BindingResult;
+import org.springframework.validation.Errors;
+import org.springframework.web.bind.WebExchangeDataBinder;
+import org.springframework.web.bind.annotation.ModelAttribute;
+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.MockWebSessionManager;
+import org.springframework.web.server.session.WebSessionManager;
+
+import static junit.framework.TestCase.assertFalse;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.springframework.core.ResolvableType.forClass;
+import static org.springframework.core.ResolvableType.forClassWithGenerics;
+
+/**
+ * Unit tests for {@link ErrorsMethodArgumentResolver}.
+ * @author Rossen Stoyanchev
+ */
+public class ErrorsArgumentResolverTests {
+
+	private ErrorsMethodArgumentResolver resolver ;
+
+	private final BindingContext bindingContext = new BindingContext();
+
+	private BindingResult bindingResult;
+
+	private ServerWebExchange exchange;
+
+	private final ResolvableMethod testMethod = ResolvableMethod.onClass(this.getClass()).name("handle");
+
+
+	@Before
+	public void setUp() throws Exception {
+		this.resolver = new ErrorsMethodArgumentResolver(new ReactiveAdapterRegistry());
+
+		MockServerHttpRequest request = new MockServerHttpRequest(HttpMethod.POST, "/path");
+		MockServerHttpResponse response = new MockServerHttpResponse();
+		WebSessionManager manager = new MockWebSessionManager();
+		this.exchange = new DefaultServerWebExchange(request, response, manager);
+
+		Foo foo = new Foo();
+		WebExchangeDataBinder binder = this.bindingContext.createDataBinder(this.exchange, foo, "foo");
+		this.bindingResult = binder.getBindingResult();
+	}
+
+
+	@Test
+	public void supports() throws Exception {
+
+		MethodParameter parameter = parameter(forClass(Errors.class));
+		assertTrue(this.resolver.supportsParameter(parameter));
+
+		parameter = parameter(forClass(BindingResult.class));
+		assertTrue(this.resolver.supportsParameter(parameter));
+
+		parameter = parameter(forClassWithGenerics(Mono.class, Errors.class));
+		assertFalse(this.resolver.supportsParameter(parameter));
+
+		parameter = parameter(forClass(String.class));
+		assertFalse(this.resolver.supportsParameter(parameter));
+	}
+
+	@Test
+	public void resolveErrors() throws Exception {
+		testResolve(this.bindingResult);
+	}
+
+	@Test
+	public void resolveErrorsMono() throws Exception {
+		MonoProcessor<BindingResult> monoProcessor = MonoProcessor.create();
+		monoProcessor.onNext(this.bindingResult);
+		testResolve(monoProcessor);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void resolveErrorsAfterMonoModelAttribute() throws Exception {
+		MethodParameter parameter = parameter(forClass(BindingResult.class));
+		this.resolver.resolveArgument(parameter, this.bindingContext, this.exchange).blockMillis(5000);
+	}
+
+
+	private void testResolve(Object bindingResult) {
+
+		String key = BindingResult.MODEL_KEY_PREFIX + "foo";
+		this.bindingContext.getModel().asMap().put(key, bindingResult);
+
+		MethodParameter parameter = parameter(forClass(Errors.class));
+
+		Object actual = this.resolver.resolveArgument(parameter, this.bindingContext, this.exchange)
+				.blockMillis(5000);
+
+		assertSame(this.bindingResult, actual);
+	}
+
+
+	private MethodParameter parameter(ResolvableType type) {
+		return this.testMethod.resolveParam(type);
+	}
+
+
+	private static class Foo {
+
+		private String name;
+
+		public Foo() {
+		}
+
+		public Foo(String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+
+	@SuppressWarnings("unused")
+	void handle(
+			@ModelAttribute Foo foo,
+			Errors errors,
+			@ModelAttribute Mono<Foo> fooMono,
+			BindingResult bindingResult,
+			Mono<Errors> errorsMono,
+			String string) {}
+
+}