/*
 * Copyright 2002-2018 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 java.util.List;

import javax.servlet.http.HttpServletRequest;

import org.springframework.core.MethodParameter;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.MultipartResolver;
import org.springframework.web.multipart.support.MissingServletRequestPartException;
import org.springframework.web.multipart.support.MultipartResolutionDelegate;
import org.springframework.web.multipart.support.RequestPartServletServerHttpRequest;

Resolves the following method arguments:

Annotated with @RequestPart 
Of type MultipartFile in conjunction with Spring's MultipartResolver abstraction 
Of type javax.servlet.http.Part in conjunction with Servlet 3.0 multipart requests 
When a parameter is annotated with @RequestPart, the content of the part is passed through an HttpMessageConverter to resolve the method argument with the 'Content-Type' of the request part in mind. This is analogous to what @RequestBody does to resolve an argument based on the content of a regular request. 
When a parameter is not annotated or the name of the part is not specified,
it is derived from the name of the method argument.
Automatic validation may be applied if the argument is annotated with @javax.validation.Valid. In case of validation failure, a MethodArgumentNotValidException is raised and a 400 response status code returned if DefaultHandlerExceptionResolver is configured. 
Author:
Rossen Stoyanchev, Brian Clozel, Juergen Hoeller
Since:
3.1/**
 * Resolves the following method arguments:
 * <ul>
 * <li>Annotated with @{@link RequestPart}
 * <li>Of type {@link MultipartFile} in conjunction with Spring's {@link MultipartResolver} abstraction
 * <li>Of type {@code javax.servlet.http.Part} in conjunction with Servlet 3.0 multipart requests
 * </ul>
 *
 * <p>When a parameter is annotated with {@code @RequestPart}, the content of the part is
 * passed through an {@link HttpMessageConverter} to resolve the method argument with the
 * 'Content-Type' of the request part in mind. This is analogous to what @{@link RequestBody}
 * does to resolve an argument based on the content of a regular request.
 *
 * <p>When a parameter is not annotated or the name of the part is not specified,
 * it is derived from the name of the method argument.
 *
 * <p>Automatic validation may be applied if the argument is annotated with
 * {@code @javax.validation.Valid}. In case of validation failure, a {@link MethodArgumentNotValidException}
 * is raised and a 400 response status code returned if
 * {@link org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver} is configured.
 *
 * @author Rossen Stoyanchev
 * @author Brian Clozel
 * @author Juergen Hoeller
 * @since 3.1
 */
public class RequestPartMethodArgumentResolver extends AbstractMessageConverterMethodArgumentResolver {

	
Basic constructor with converters only.
/**
	 * Basic constructor with converters only.
	 */
	public RequestPartMethodArgumentResolver(List<HttpMessageConverter<?>> messageConverters) {
		super(messageConverters);
	}

	
Constructor with converters and Request~ and ResponseBodyAdvice. /**
	 * Constructor with converters and {@code Request~} and
	 * {@code ResponseBodyAdvice}.
	 */
	public RequestPartMethodArgumentResolver(List<HttpMessageConverter<?>> messageConverters,
			List<Object> requestResponseBodyAdvice) {

		super(messageConverters, requestResponseBodyAdvice);
	}


	
Whether the given method parameter is a multi-part supported. Supports the following: 

annotated with @RequestPart 
of type MultipartFile unless annotated with @RequestParam 
of type javax.servlet.http.Part unless annotated with @RequestParam 
/**
	 * Whether the given {@linkplain MethodParameter method parameter} is a multi-part
	 * supported. Supports the following:
	 * <ul>
	 * <li>annotated with {@code @RequestPart}
	 * <li>of type {@link MultipartFile} unless annotated with {@code @RequestParam}
	 * <li>of type {@code javax.servlet.http.Part} unless annotated with
	 * {@code @RequestParam}
	 * </ul>
	 */
	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		if (parameter.hasParameterAnnotation(RequestPart.class)) {
			return true;
		}
		else {
			if (parameter.hasParameterAnnotation(RequestParam.class)) {
				return false;
			}
			return MultipartResolutionDelegate.isMultipartArgument(parameter.nestedIfOptional());
		}
	}

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

		HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);
		Assert.state(servletRequest != null, "No HttpServletRequest");

		RequestPart requestPart = parameter.getParameterAnnotation(RequestPart.class);
		boolean isRequired = ((requestPart == null || requestPart.required()) && !parameter.isOptional());

		String name = getPartName(parameter, requestPart);
		parameter = parameter.nestedIfOptional();
		Object arg = null;

		Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);
		if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
			arg = mpArg;
		}
		else {
			try {
				HttpInputMessage inputMessage = new RequestPartServletServerHttpRequest(servletRequest, name);
				arg = readWithMessageConverters(inputMessage, parameter, parameter.getNestedGenericParameterType());
				if (binderFactory != null) {
					WebDataBinder binder = binderFactory.createBinder(request, arg, name);
					if (arg != null) {
						validateIfApplicable(binder, parameter);
						if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
							throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
						}
					}
					if (mavContainer != null) {
						mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
					}
				}
			}
			catch (MissingServletRequestPartException | MultipartException ex) {
				if (isRequired) {
					throw ex;
				}
			}
		}

		if (arg == null && isRequired) {
			if (!MultipartResolutionDelegate.isMultipartRequest(servletRequest)) {
				throw new MultipartException("Current request is not a multipart request");
			}
			else {
				throw new MissingServletRequestPartException(name);
			}
		}
		return adaptArgumentIfNecessary(arg, parameter);
	}

	private String getPartName(MethodParameter methodParam, @Nullable RequestPart requestPart) {
		String partName = (requestPart != null ? requestPart.name() : "");
		if (partName.isEmpty()) {
			partName = methodParam.getParameterName();
			if (partName == null) {
				throw new IllegalArgumentException("Request part name for argument type [" +
						methodParam.getNestedParameterType().getName() +
						"] not specified, and parameter name information not found in class file either.");
			}
		}
		return partName;
	}

}