001/*
002 * Copyright 2002-2019 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.servlet.mvc.method.annotation;
018
019import org.springframework.core.MethodParameter;
020import org.springframework.util.PatternMatchUtils;
021import org.springframework.web.context.request.NativeWebRequest;
022import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
023import org.springframework.web.method.support.ModelAndViewContainer;
024import org.springframework.web.servlet.RequestToViewNameTranslator;
025
026/**
027 * Handles return values of types {@code void} and {@code String} interpreting them
028 * as view name reference. As of 4.2, it also handles general {@code CharSequence}
029 * types, e.g. {@code StringBuilder} or Groovy's {@code GString}, as view names.
030 *
031 * <p>A {@code null} return value, either due to a {@code void} return type or
032 * as the actual return value is left as-is allowing the configured
033 * {@link RequestToViewNameTranslator} to select a view name by convention.
034 *
035 * <p>A String return value can be interpreted in more than one ways depending on
036 * the presence of annotations like {@code @ModelAttribute} or {@code @ResponseBody}.
037 * Therefore this handler should be configured after the handlers that support these
038 * annotations.
039 *
040 * @author Rossen Stoyanchev
041 * @author Juergen Hoeller
042 * @since 3.1
043 */
044public class ViewNameMethodReturnValueHandler implements HandlerMethodReturnValueHandler {
045
046        private String[] redirectPatterns;
047
048
049        /**
050         * Configure one more simple patterns (as described in {@link PatternMatchUtils#simpleMatch})
051         * to use in order to recognize custom redirect prefixes in addition to "redirect:".
052         * <p>Note that simply configuring this property will not make a custom redirect prefix work.
053         * There must be a custom View that recognizes the prefix as well.
054         * @since 4.1
055         */
056        public void setRedirectPatterns(String... redirectPatterns) {
057                this.redirectPatterns = redirectPatterns;
058        }
059
060        /**
061         * The configured redirect patterns, if any.
062         */
063        public String[] getRedirectPatterns() {
064                return this.redirectPatterns;
065        }
066
067
068        @Override
069        public boolean supportsReturnType(MethodParameter returnType) {
070                Class<?> paramType = returnType.getParameterType();
071                return (void.class == paramType || CharSequence.class.isAssignableFrom(paramType));
072        }
073
074        @Override
075        public void handleReturnValue(Object returnValue, MethodParameter returnType,
076                        ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
077
078                if (returnValue instanceof CharSequence) {
079                        String viewName = returnValue.toString();
080                        mavContainer.setViewName(viewName);
081                        if (isRedirectViewName(viewName)) {
082                                mavContainer.setRedirectModelScenario(true);
083                        }
084                }
085                else if (returnValue != null) {
086                        // should not happen
087                        throw new UnsupportedOperationException("Unexpected return type: " +
088                                        returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
089                }
090        }
091
092        /**
093         * Whether the given view name is a redirect view reference.
094         * The default implementation checks the configured redirect patterns and
095         * also if the view name starts with the "redirect:" prefix.
096         * @param viewName the view name to check, never {@code null}
097         * @return "true" if the given view name is recognized as a redirect view
098         * reference; "false" otherwise.
099         */
100        protected boolean isRedirectViewName(String viewName) {
101                return (PatternMatchUtils.simpleMatch(this.redirectPatterns, viewName) || viewName.startsWith("redirect:"));
102        }
103
104}