spring-graphql HandlerMethodArgumentResolverComposite 源码

spring-graphql HandlerMethodArgumentResolverComposite 代码

文件路径：/spring-graphql/src/main/java/org/springframework/graphql/data/method/HandlerMethodArgumentResolverComposite.java

/*
 * Copyright 2002-2021 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.graphql.data.method;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import graphql.schema.DataFetchingEnvironment;

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;

/**
 * Resolves method parameters by delegating to a list of registered
 * {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolver}'s.
 * Previously resolved method parameters are cached for faster lookups.
 *
 * @author Rossen Stoyanchev
 * @since 1.0.0
 */
public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {

	private final List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList<>();

	private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache =
			new ConcurrentHashMap<>(256);


	/**
	 * Add the given {@link HandlerMethodArgumentResolver}.
	 */
	public void addResolver(HandlerMethodArgumentResolver resolver) {
		this.argumentResolvers.add(resolver);
	}

	/**
	 * Return a read-only list with the contained resolvers, or an empty list.
	 */
	public List<HandlerMethodArgumentResolver> getResolvers() {
		return Collections.unmodifiableList(this.argumentResolvers);
	}


	/**
	 * Whether the given {@linkplain MethodParameter method parameter} is
	 * supported by any registered {@link HandlerMethodArgumentResolver}.
	 */
	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return getArgumentResolver(parameter) != null;
	}

	/**
	 * Iterate over registered
	 * {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}
	 * and invoke the one that supports it.
	 * @throws IllegalArgumentException if no suitable argument resolver is found
	 */
	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, DataFetchingEnvironment environment) throws Exception {
		HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
		if (resolver == null) {
			throw new IllegalArgumentException("Unsupported parameter type [" +
					parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
		}
		return resolver.resolveArgument(parameter, environment);
	}

	/**
	 * Find a registered {@link HandlerMethodArgumentResolver} that supports
	 * the given method parameter.
	 */
	@Nullable
	public HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
		HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
		if (result == null) {
			for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {
				if (resolver.supportsParameter(parameter)) {
					result = resolver;
					this.argumentResolverCache.put(parameter, result);
					break;
				}
			}
		}
		return result;
	}

}

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