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.lang.Nullable;
021import org.springframework.util.PatternMatchUtils;
022import org.springframework.web.context.request.NativeWebRequest;
023import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
024import org.springframework.web.method.support.ModelAndViewContainer;
025import org.springframework.web.servlet.RequestToViewNameTranslator;
026
027/**
028 * Handles return values of types {@code void} and {@code String} interpreting them
029 * as view name reference. As of 4.2, it also handles general {@code CharSequence}
030 * types, e.g. {@code StringBuilder} or Groovy's {@code GString}, as view names.
031 *
032 * <p>A {@code null} return value, either due to a {@code void} return type or
033 * as the actual return value is left as-is allowing the configured
034 * {@link RequestToViewNameTranslator} to select a view name by convention.
035 *
036 * <p>A String return value can be interpreted in more than one ways depending on
037 * the presence of annotations like {@code @ModelAttribute} or {@code @ResponseBody}.
038 * Therefore this handler should be configured after the handlers that support these
039 * annotations.
040 *
041 * @author Rossen Stoyanchev
042 * @author Juergen Hoeller
043 * @since 3.1
044 */
045public class ViewNameMethodReturnValueHandler implements HandlerMethodReturnValueHandler {
046
047        @Nullable
048        private String[] redirectPatterns;
049
050
051        /**
052         * Configure one more simple patterns (as described in {@link PatternMatchUtils#simpleMatch})
053         * to use in order to recognize custom redirect prefixes in addition to "redirect:".
054         * <p>Note that simply configuring this property will not make a custom redirect prefix work.
055         * There must be a custom View that recognizes the prefix as well.
056         * @since 4.1
057         */
058        public void setRedirectPatterns(@Nullable String... redirectPatterns) {
059                this.redirectPatterns = redirectPatterns;
060        }
061
062        /**
063         * The configured redirect patterns, if any.
064         */
065        @Nullable
066        public String[] getRedirectPatterns() {
067                return this.redirectPatterns;
068        }
069
070
071        @Override
072        public boolean supportsReturnType(MethodParameter returnType) {
073                Class<?> paramType = returnType.getParameterType();
074                return (void.class == paramType || CharSequence.class.isAssignableFrom(paramType));
075        }
076
077        @Override
078        public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
079                        ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
080
081                if (returnValue instanceof CharSequence) {
082                        String viewName = returnValue.toString();
083                        mavContainer.setViewName(viewName);
084                        if (isRedirectViewName(viewName)) {
085                                mavContainer.setRedirectModelScenario(true);
086                        }
087                }
088                else if (returnValue != null) {
089                        // should not happen
090                        throw new UnsupportedOperationException("Unexpected return type: " +
091                                        returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
092                }
093        }
094
095        /**
096         * Whether the given view name is a redirect view reference.
097         * The default implementation checks the configured redirect patterns and
098         * also if the view name starts with the "redirect:" prefix.
099         * @param viewName the view name to check, never {@code null}
100         * @return "true" if the given view name is recognized as a redirect view
101         * reference; "false" otherwise.
102         */
103        protected boolean isRedirectViewName(String viewName) {
104                return (PatternMatchUtils.simpleMatch(this.redirectPatterns, viewName) || viewName.startsWith("redirect:"));
105        }
106
107}