/*
 * Copyright 2002-2019 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
 *
 *      https://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.servlet.mvc.method.annotation;

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.util.PatternMatchUtils;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.RequestToViewNameTranslator;

Handles return values of types void and String interpreting them as view name reference. As of 4.2, it also handles general CharSequence types, e.g. StringBuilder or Groovy's GString, as view names. 
A null return value, either due to a void return type or as the actual return value is left as-is allowing the configured RequestToViewNameTranslator to select a view name by convention. 
A String return value can be interpreted in more than one ways depending on the presence of annotations like @ModelAttribute or @ResponseBody. Therefore this handler should be configured after the handlers that support these annotations. 
Author:
Rossen Stoyanchev, Juergen Hoeller
Since:
3.1/**
 * Handles return values of types {@code void} and {@code String} interpreting them
 * as view name reference. As of 4.2, it also handles general {@code CharSequence}
 * types, e.g. {@code StringBuilder} or Groovy's {@code GString}, as view names.
 *
 * <p>A {@code null} return value, either due to a {@code void} return type or
 * as the actual return value is left as-is allowing the configured
 * {@link RequestToViewNameTranslator} to select a view name by convention.
 *
 * <p>A String return value can be interpreted in more than one ways depending on
 * the presence of annotations like {@code @ModelAttribute} or {@code @ResponseBody}.
 * Therefore this handler should be configured after the handlers that support these
 * annotations.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 3.1
 */
public class ViewNameMethodReturnValueHandler implements HandlerMethodReturnValueHandler {

	@Nullable
	private String[] redirectPatterns;


	
Configure one more simple patterns (as described in PatternMatchUtils.simpleMatch) to use in order to recognize custom redirect prefixes in addition to "redirect:". 
Note that simply configuring this property will not make a custom redirect prefix work.
There must be a custom View that recognizes the prefix as well.
Since:
4.1/**
	 * Configure one more simple patterns (as described in {@link PatternMatchUtils#simpleMatch})
	 * to use in order to recognize custom redirect prefixes in addition to "redirect:".
	 * <p>Note that simply configuring this property will not make a custom redirect prefix work.
	 * There must be a custom View that recognizes the prefix as well.
	 * @since 4.1
	 */
	public void setRedirectPatterns(@Nullable String... redirectPatterns) {
		this.redirectPatterns = redirectPatterns;
	}

	
The configured redirect patterns, if any.
/**
	 * The configured redirect patterns, if any.
	 */
	@Nullable
	public String[] getRedirectPatterns() {
		return this.redirectPatterns;
	}


	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
		Class<?> paramType = returnType.getParameterType();
		return (void.class == paramType || CharSequence.class.isAssignableFrom(paramType));
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

		if (returnValue instanceof CharSequence) {
			String viewName = returnValue.toString();
			mavContainer.setViewName(viewName);
			if (isRedirectViewName(viewName)) {
				mavContainer.setRedirectModelScenario(true);
			}
		}
		else if (returnValue != null) {
			// should not happen
			throw new UnsupportedOperationException("Unexpected return type: " +
					returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
		}
	}

	
Whether the given view name is a redirect view reference.
The default implementation checks the configured redirect patterns and
also if the view name starts with the "redirect:" prefix.
Params:
viewName – the view name to check, never null
Returns:
"true" if the given view name is recognized as a redirect view
reference; "false" otherwise./**
	 * Whether the given view name is a redirect view reference.
	 * The default implementation checks the configured redirect patterns and
	 * also if the view name starts with the "redirect:" prefix.
	 * @param viewName the view name to check, never {@code null}
	 * @return "true" if the given view name is recognized as a redirect view
	 * reference; "false" otherwise.
	 */
	protected boolean isRedirectViewName(String viewName) {
		return (PatternMatchUtils.simpleMatch(this.redirectPatterns, viewName) || viewName.startsWith("redirect:"));
	}

}