001/*
002 * Copyright 2002-2018 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.web.method.annotation;
018
019import org.springframework.core.MethodParameter;
020import org.springframework.lang.Nullable;
021import org.springframework.ui.ModelMap;
022import org.springframework.util.Assert;
023import org.springframework.util.CollectionUtils;
024import org.springframework.validation.BindingResult;
025import org.springframework.validation.Errors;
026import org.springframework.web.bind.support.WebDataBinderFactory;
027import org.springframework.web.context.request.NativeWebRequest;
028import org.springframework.web.method.support.HandlerMethodArgumentResolver;
029import org.springframework.web.method.support.ModelAndViewContainer;
030
031/**
032 * Resolves {@link Errors} method arguments.
033 *
034 * <p>An {@code Errors} method argument is expected to appear immediately after
035 * the model attribute in the method signature. It is resolved by expecting the
036 * last two attributes added to the model to be the model attribute and its
037 * {@link BindingResult}.
038 *
039 * @author Rossen Stoyanchev
040 * @author Juergen Hoeller
041 * @since 3.1
042 */
043public class ErrorsMethodArgumentResolver implements HandlerMethodArgumentResolver {
044
045        @Override
046        public boolean supportsParameter(MethodParameter parameter) {
047                Class<?> paramType = parameter.getParameterType();
048                return Errors.class.isAssignableFrom(paramType);
049        }
050
051        @Override
052        @Nullable
053        public Object resolveArgument(MethodParameter parameter,
054                        @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
055                        @Nullable WebDataBinderFactory binderFactory) throws Exception {
056
057                Assert.state(mavContainer != null,
058                                "Errors/BindingResult argument only supported on regular handler methods");
059
060                ModelMap model = mavContainer.getModel();
061                String lastKey = CollectionUtils.lastElement(model.keySet());
062                if (lastKey != null && lastKey.startsWith(BindingResult.MODEL_KEY_PREFIX)) {
063                        return model.get(lastKey);
064                }
065
066                throw new IllegalStateException(
067                                "An Errors/BindingResult argument is expected to be declared immediately after " +
068                                "the model attribute, the @RequestBody or the @RequestPart arguments " +
069                                "to which they apply: " + parameter.getMethod());
070        }
071
072}