spring MessageMethodArgumentResolver 源码

spring MessageMethodArgumentResolver 代码

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

import java.lang.reflect.Type;

import org.springframework.core.MethodParameter;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;
import org.springframework.messaging.Message;
import org.springframework.messaging.converter.MessageConversionException;
import org.springframework.messaging.converter.MessageConverter;
import org.springframework.messaging.converter.SmartMessageConverter;
import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver;
import org.springframework.messaging.support.MessageBuilder;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * {@code HandlerMethodArgumentResolver} for {@link Message} method arguments.
 * Validates that the generic type of the payload matches to the message value
 * or otherwise applies {@link MessageConverter} to convert to the expected
 * payload type.
 *
 * @author Rossen Stoyanchev
 * @author Stephane Nicoll
 * @author Juergen Hoeller
 * @since 4.0
 */
public class MessageMethodArgumentResolver implements HandlerMethodArgumentResolver {

	@Nullable
	private final MessageConverter converter;


	/**
	 * Create a default resolver instance without message conversion.
	 */
	public MessageMethodArgumentResolver() {
		this(null);
	}

	/**
	 * Create a resolver instance with the given {@link MessageConverter}.
	 * @param converter the MessageConverter to use (may be {@code null})
	 * @since 4.3
	 */
	public MessageMethodArgumentResolver(@Nullable MessageConverter converter) {
		this.converter = converter;
	}


	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return Message.class.isAssignableFrom(parameter.getParameterType());
	}

	@Override
	public Object resolveArgument(MethodParameter parameter, Message<?> message) throws Exception {
		Class<?> targetMessageType = parameter.getParameterType();
		Class<?> targetPayloadType = getPayloadType(parameter, message);

		if (!targetMessageType.isAssignableFrom(message.getClass())) {
			throw new MethodArgumentTypeMismatchException(message, parameter, "Actual message type '" +
					ClassUtils.getDescriptiveType(message) + "' does not match expected type '" +
					ClassUtils.getQualifiedName(targetMessageType) + "'");
		}

		Object payload = message.getPayload();
		if (targetPayloadType.isInstance(payload)) {
			return message;
		}

		if (isEmptyPayload(payload)) {
			throw new MessageConversionException(message, "Cannot convert from actual payload type '" +
					ClassUtils.getDescriptiveType(payload) + "' to expected payload type '" +
					ClassUtils.getQualifiedName(targetPayloadType) + "' when payload is empty");
		}

		payload = convertPayload(message, parameter, targetPayloadType);
		return MessageBuilder.createMessage(payload, message.getHeaders());
	}

	/**
	 * Resolve the target class to convert the payload to.
	 * <p>By default this is the generic type declared in the {@code Message}
	 * method parameter but that can be overridden to select a more specific
	 * target type after also taking into account the "Content-Type", e.g.
	 * return {@code String} if target type is {@code Object} and
	 * {@code "Content-Type:text/**"}.
	 * @param parameter the target method parameter
	 * @param message the message being processed
	 * @return the target type to use
	 * @since 5.2
	 */
	protected Class<?> getPayloadType(MethodParameter parameter, Message<?> message) {
		Type genericParamType = parameter.getGenericParameterType();
		ResolvableType resolvableType = ResolvableType.forType(genericParamType).as(Message.class);
		return resolvableType.getGeneric().toClass();
	}

	/**
	 * Check if the given {@code payload} is empty.
	 * @param payload the payload to check (can be {@code null})
	 */
	protected boolean isEmptyPayload(@Nullable Object payload) {
		if (payload == null) {
			return true;
		}
		else if (payload instanceof byte[]) {
			return ((byte[]) payload).length == 0;
		}
		else if (payload instanceof String) {
			return !StringUtils.hasText((String) payload);
		}
		else {
			return false;
		}
	}

	private Object convertPayload(Message<?> message, MethodParameter parameter, Class<?> targetPayloadType) {
		Object result = null;
		if (this.converter instanceof SmartMessageConverter smartConverter) {
			result = smartConverter.fromMessage(message, targetPayloadType, parameter);
		}
		else if (this.converter != null) {
			result = this.converter.fromMessage(message, targetPayloadType);
		}

		if (result == null) {
			throw new MessageConversionException(message, "No converter found from actual payload type '" +
					ClassUtils.getDescriptiveType(message.getPayload()) + "' to expected payload type '" +
					ClassUtils.getQualifiedName(targetPayloadType) + "'");
		}
		return result;
	}

}

相关信息

spring 源码目录

相关文章

spring AbstractNamedValueMethodArgumentResolver 源码

spring AnnotationExceptionHandlerMethodResolver 源码

spring DefaultMessageHandlerMethodFactory 源码

spring DestinationVariableMethodArgumentResolver 源码

spring HeaderMethodArgumentResolver 源码

spring HeadersMethodArgumentResolver 源码

spring MessageHandlerMethodFactory 源码

spring MethodArgumentNotValidException 源码

spring MethodArgumentTypeMismatchException 源码

spring PayloadMethodArgumentResolver 源码