spring HeadersMethodArgumentResolver 源码

spring HeadersMethodArgumentResolver 代码

文件路径：/spring-messaging/src/main/java/org/springframework/messaging/handler/annotation/support/HeadersMethodArgumentResolver.java

/*
 * 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.messaging.handler.annotation.support;

import java.lang.reflect.Method;
import java.util.Map;

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHeaders;
import org.springframework.messaging.handler.annotation.Headers;
import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver;
import org.springframework.messaging.support.MessageHeaderAccessor;
import org.springframework.util.ReflectionUtils;

/**
 * Argument resolver for headers. Resolves the following method parameters:
 * <ul>
 * <li>{@link Headers @Headers} {@link Map}
 * <li>{@link MessageHeaders}
 * <li>{@link MessageHeaderAccessor}
 * </ul>
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 */
public class HeadersMethodArgumentResolver implements HandlerMethodArgumentResolver {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		Class<?> paramType = parameter.getParameterType();
		return ((parameter.hasParameterAnnotation(Headers.class) && Map.class.isAssignableFrom(paramType)) ||
				MessageHeaders.class == paramType || MessageHeaderAccessor.class.isAssignableFrom(paramType));
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, Message<?> message) throws Exception {
		Class<?> paramType = parameter.getParameterType();
		if (Map.class.isAssignableFrom(paramType)) {
			return message.getHeaders();
		}
		else if (MessageHeaderAccessor.class == paramType) {
			MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, MessageHeaderAccessor.class);
			return accessor != null ? accessor : new MessageHeaderAccessor(message);
		}
		else if (MessageHeaderAccessor.class.isAssignableFrom(paramType)) {
			MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, MessageHeaderAccessor.class);
			if (accessor != null && paramType.isAssignableFrom(accessor.getClass())) {
				return accessor;
			}
			else {
				Method method = ReflectionUtils.findMethod(paramType, "wrap", Message.class);
				if (method == null) {
					throw new IllegalStateException(
							"Cannot create accessor of type " + paramType + " for message " + message);
				}
				return ReflectionUtils.invokeMethod(method, null, message);
			}
		}
		else {
			throw new IllegalStateException("Unexpected parameter of type " + paramType +
					" in method " + parameter.getMethod() + ". ");
		}
	}

}

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