spring MessageBuilder 源码

spring MessageBuilder 代码

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

import java.util.Map;

import org.springframework.lang.Nullable;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.MessageHeaders;
import org.springframework.util.Assert;

/**
 * A builder for creating a {@link GenericMessage}
 * (or {@link ErrorMessage} if the payload is of type {@link Throwable}).
 *
 * @author Arjen Poutsma
 * @author Mark Fisher
 * @author Rossen Stoyanchev
 * @since 4.0
 * @param <T> the message payload type
 * @see GenericMessage
 * @see ErrorMessage
 */
public final class MessageBuilder<T> {

	private final T payload;

	@Nullable
	private final Message<T> providedMessage;

	private MessageHeaderAccessor headerAccessor;


	private MessageBuilder(Message<T> providedMessage) {
		Assert.notNull(providedMessage, "Message must not be null");
		this.payload = providedMessage.getPayload();
		this.providedMessage = providedMessage;
		this.headerAccessor = new MessageHeaderAccessor(providedMessage);
	}

	private MessageBuilder(T payload, MessageHeaderAccessor accessor) {
		Assert.notNull(payload, "Payload must not be null");
		Assert.notNull(accessor, "MessageHeaderAccessor must not be null");
		this.payload = payload;
		this.providedMessage = null;
		this.headerAccessor = accessor;
	}


	/**
	 * Set the message headers to use by providing a {@code MessageHeaderAccessor}.
	 * @param accessor the headers to use
	 */
	public MessageBuilder<T> setHeaders(MessageHeaderAccessor accessor) {
		Assert.notNull(accessor, "MessageHeaderAccessor must not be null");
		this.headerAccessor = accessor;
		return this;
	}

	/**
	 * Set the value for the given header name. If the provided value is {@code null},
	 * the header will be removed.
	 */
	public MessageBuilder<T> setHeader(String headerName, @Nullable Object headerValue) {
		this.headerAccessor.setHeader(headerName, headerValue);
		return this;
	}

	/**
	 * Set the value for the given header name only if the header name is not already
	 * associated with a value.
	 */
	public MessageBuilder<T> setHeaderIfAbsent(String headerName, Object headerValue) {
		this.headerAccessor.setHeaderIfAbsent(headerName, headerValue);
		return this;
	}

	/**
	 * Removes all headers provided via array of 'headerPatterns'. As the name suggests
	 * the array may contain simple matching patterns for header names. Supported pattern
	 * styles are: "xxx*", "*xxx", "*xxx*" and "xxx*yyy".
	 */
	public MessageBuilder<T> removeHeaders(String... headerPatterns) {
		this.headerAccessor.removeHeaders(headerPatterns);
		return this;
	}

	/**
	 * Remove the value for the given header name.
	 */
	public MessageBuilder<T> removeHeader(String headerName) {
		this.headerAccessor.removeHeader(headerName);
		return this;
	}

	/**
	 * Copy the name-value pairs from the provided Map. This operation will overwrite any
	 * existing values. Use {@link #copyHeadersIfAbsent(Map)} to avoid overwriting
	 * values. Note that the 'id' and 'timestamp' header values will never be overwritten.
	 */
	public MessageBuilder<T> copyHeaders(@Nullable Map<String, ?> headersToCopy) {
		this.headerAccessor.copyHeaders(headersToCopy);
		return this;
	}

	/**
	 * Copy the name-value pairs from the provided Map. This operation will <em>not</em>
	 * overwrite any existing values.
	 */
	public MessageBuilder<T> copyHeadersIfAbsent(@Nullable Map<String, ?> headersToCopy) {
		this.headerAccessor.copyHeadersIfAbsent(headersToCopy);
		return this;
	}

	public MessageBuilder<T> setReplyChannel(MessageChannel replyChannel) {
		this.headerAccessor.setReplyChannel(replyChannel);
		return this;
	}

	public MessageBuilder<T> setReplyChannelName(String replyChannelName) {
		this.headerAccessor.setReplyChannelName(replyChannelName);
		return this;
	}

	public MessageBuilder<T> setErrorChannel(MessageChannel errorChannel) {
		this.headerAccessor.setErrorChannel(errorChannel);
		return this;
	}

	public MessageBuilder<T> setErrorChannelName(String errorChannelName) {
		this.headerAccessor.setErrorChannelName(errorChannelName);
		return this;
	}

	@SuppressWarnings("unchecked")
	public Message<T> build() {
		if (this.providedMessage != null && !this.headerAccessor.isModified()) {
			return this.providedMessage;
		}
		MessageHeaders headersToUse = this.headerAccessor.toMessageHeaders();
		if (this.payload instanceof Throwable) {
			if (this.providedMessage != null && this.providedMessage instanceof ErrorMessage) {
				Message<?> message = ((ErrorMessage) this.providedMessage).getOriginalMessage();
				if (message != null) {
					return (Message<T>) new ErrorMessage((Throwable) this.payload, headersToUse, message);
				}
			}
			return (Message<T>) new ErrorMessage((Throwable) this.payload, headersToUse);
		}
		else {
			return new GenericMessage<>(this.payload, headersToUse);
		}
	}


	/**
	 * Create a builder for a new {@link Message} instance pre-populated with all the
	 * headers copied from the provided message. The payload of the provided Message will
	 * also be used as the payload for the new message.
	 * <p>If the provided message is an {@link ErrorMessage}, the
	 * {@link ErrorMessage#getOriginalMessage() originalMessage} it contains, will be
	 * passed on to new instance.
	 * @param message the Message from which the payload and all headers will be copied
	 */
	public static <T> MessageBuilder<T> fromMessage(Message<T> message) {
		return new MessageBuilder<>(message);
	}

	/**
	 * Create a new builder for a message with the given payload.
	 * @param payload the payload
	 */
	public static <T> MessageBuilder<T> withPayload(T payload) {
		return new MessageBuilder<>(payload, new MessageHeaderAccessor());
	}

	/**
	 * A shortcut factory method for creating a message with the given payload
	 * and {@code MessageHeaders}.
	 * <p><strong>Note:</strong> the given {@code MessageHeaders} instance is used
	 * directly in the new message, i.e. it is not copied.
	 * @param payload the payload to use (never {@code null})
	 * @param messageHeaders the headers to use (never {@code null})
	 * @return the created message
	 * @since 4.1
	 */
	@SuppressWarnings("unchecked")
	public static <T> Message<T> createMessage(@Nullable T payload, MessageHeaders messageHeaders) {
		Assert.notNull(payload, "Payload must not be null");
		Assert.notNull(messageHeaders, "MessageHeaders must not be null");
		if (payload instanceof Throwable) {
			return (Message<T>) new ErrorMessage((Throwable) payload, messageHeaders);
		}
		else {
			return new GenericMessage<>(payload, messageHeaders);
		}
	}

}

相关信息

spring 源码目录

相关文章

spring AbstractHeaderMapper 源码

spring AbstractMessageChannel 源码

spring AbstractSubscribableChannel 源码

spring ChannelInterceptor 源码

spring ErrorMessage 源码

spring ExecutorChannelInterceptor 源码

spring ExecutorSubscribableChannel 源码

spring GenericMessage 源码

spring HeaderMapper 源码

spring IdTimestampMessageHeaderInitializer 源码