001/*
002 * Copyright 2002-2017 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.bind.support;
018
019import org.springframework.core.MethodParameter;
020import org.springframework.lang.Nullable;
021import org.springframework.web.context.request.NativeWebRequest;
022
023/**
024 * SPI for resolving custom arguments for a specific handler method parameter.
025 * Typically implemented to detect special parameter types, resolving
026 * well-known argument values for them.
027 *
028 * <p>A typical implementation could look like as follows:
029 *
030 * <pre class="code">
031 * public class MySpecialArgumentResolver implements WebArgumentResolver {
032 *
033 *   public Object resolveArgument(MethodParameter methodParameter, NativeWebRequest webRequest) {
034 *     if (methodParameter.getParameterType().equals(MySpecialArg.class)) {
035 *       return new MySpecialArg("myValue");
036 *     }
037 *     return UNRESOLVED;
038 *   }
039 * }</pre>
040 *
041 * @author Juergen Hoeller
042 * @since 2.5.2
043 * @see org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#setCustomArgumentResolvers
044 */
045@FunctionalInterface
046public interface WebArgumentResolver {
047
048        /**
049         * Marker to be returned when the resolver does not know how to
050         * handle the given method parameter.
051         */
052        Object UNRESOLVED = new Object();
053
054
055        /**
056         * Resolve an argument for the given handler method parameter within the given web request.
057         * @param methodParameter the handler method parameter to resolve
058         * @param webRequest the current web request, allowing access to the native request as well
059         * @return the argument value, or {@code UNRESOLVED} if not resolvable
060         * @throws Exception in case of resolution failure
061         */
062        @Nullable
063        Object resolveArgument(MethodParameter methodParameter, NativeWebRequest webRequest) throws Exception;
064
065}