/*
 * Copyright 2002-2020 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.method.annotation;

import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.Part;

import org.springframework.core.MethodParameter;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.MultipartRequest;
import org.springframework.web.multipart.support.MultipartResolutionDelegate;

Resolves Map method arguments annotated with an @RequestParam where the annotation does not specify a request parameter name. 
The created Map contains all request parameter name/value pairs, or all multipart files for a given parameter name if specifically declared with MultipartFile as the value type. If the method parameter type is MultiValueMap instead, the created map contains all request parameters and all their values for cases where request parameters have multiple values (or multiple multipart files of the same name). 
Author:
Arjen Poutsma, Rossen Stoyanchev, Juergen Hoeller
See Also:
RequestParamMethodArgumentResolver
getParameterMap.getParameterMap()
MultipartRequest.getMultiFileMap()
MultipartRequest.getFileMap()
Since:
3.1/**
 * Resolves {@link Map} method arguments annotated with an @{@link RequestParam}
 * where the annotation does not specify a request parameter name.
 *
 * <p>The created {@link Map} contains all request parameter name/value pairs,
 * or all multipart files for a given parameter name if specifically declared
 * with {@link MultipartFile} as the value type. If the method parameter type is
 * {@link MultiValueMap} instead, the created map contains all request parameters
 * and all their values for cases where request parameters have multiple values
 * (or multiple multipart files of the same name).
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 3.1
 * @see RequestParamMethodArgumentResolver
 * @see HttpServletRequest#getParameterMap()
 * @see MultipartRequest#getMultiFileMap()
 * @see MultipartRequest#getFileMap()
 */
public class RequestParamMapMethodArgumentResolver implements HandlerMethodArgumentResolver {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		RequestParam requestParam = parameter.getParameterAnnotation(RequestParam.class);
		return (requestParam != null && Map.class.isAssignableFrom(parameter.getParameterType()) &&
				!StringUtils.hasText(requestParam.name()));
	}

	@Override
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		ResolvableType resolvableType = ResolvableType.forMethodParameter(parameter);

		if (MultiValueMap.class.isAssignableFrom(parameter.getParameterType())) {
			// MultiValueMap
			Class<?> valueType = resolvableType.as(MultiValueMap.class).getGeneric(1).resolve();
			if (valueType == MultipartFile.class) {
				MultipartRequest multipartRequest = MultipartResolutionDelegate.resolveMultipartRequest(webRequest);
				return (multipartRequest != null ? multipartRequest.getMultiFileMap() : new LinkedMultiValueMap<>(0));
			}
			else if (valueType == Part.class) {
				HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
				if (servletRequest != null && MultipartResolutionDelegate.isMultipartRequest(servletRequest)) {
					Collection<Part> parts = servletRequest.getParts();
					LinkedMultiValueMap<String, Part> result = new LinkedMultiValueMap<>(parts.size());
					for (Part part : parts) {
						result.add(part.getName(), part);
					}
					return result;
				}
				return new LinkedMultiValueMap<>(0);
			}
			else {
				Map<String, String[]> parameterMap = webRequest.getParameterMap();
				MultiValueMap<String, String> result = new LinkedMultiValueMap<>(parameterMap.size());
				parameterMap.forEach((key, values) -> {
					for (String value : values) {
						result.add(key, value);
					}
				});
				return result;
			}
		}

		else {
			// Regular Map
			Class<?> valueType = resolvableType.asMap().getGeneric(1).resolve();
			if (valueType == MultipartFile.class) {
				MultipartRequest multipartRequest = MultipartResolutionDelegate.resolveMultipartRequest(webRequest);
				return (multipartRequest != null ? multipartRequest.getFileMap() : new LinkedHashMap<>(0));
			}
			else if (valueType == Part.class) {
				HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
				if (servletRequest != null && MultipartResolutionDelegate.isMultipartRequest(servletRequest)) {
					Collection<Part> parts = servletRequest.getParts();
					LinkedHashMap<String, Part> result = CollectionUtils.newLinkedHashMap(parts.size());
					for (Part part : parts) {
						if (!result.containsKey(part.getName())) {
							result.put(part.getName(), part);
						}
					}
					return result;
				}
				return new LinkedHashMap<>(0);
			}
			else {
				Map<String, String[]> parameterMap = webRequest.getParameterMap();
				Map<String, String> result = CollectionUtils.newLinkedHashMap(parameterMap.size());
				parameterMap.forEach((key, values) -> {
					if (values.length > 0) {
						result.put(key, values[0]);
					}
				});
				return result;
			}
		}
	}

}