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MessageRoutingCallback.java
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MessageRoutingCallback.java
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/*
* Copyright 2021-2021 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.cloud.function.context;
import org.springframework.cloud.function.context.config.RoutingFunction;
import org.springframework.messaging.Message;
/**
* Java-based strategy to assist with determining the name of the route-to function definition.
* Once implementation is registered as a bean in application context
* it will be picked up by the {@link RoutingFunction}.
*
* While {@link RoutingFunction} provides several mechanisms to determine the route-to function definition
* this callback takes precedence over all of them.
*
* @author Oleg Zhurakousky
* @since 3.1
*/
public interface MessageRoutingCallback {
/**
* Computes and returns the instance of {@link FunctionRoutingResult} which encapsulates,
* at the very minimum, function definition.
* <br><br>
* Providing such message is primarily an optimization feature. It could be useful for cases
* where routing procedure is complex and results in, let's say, conversion of the payload to
* the target type, which would effectively be thrown away if the ability to modify the target
* message for downstream use didn't exist, resulting in repeated transformation, type conversion etc.
*
* @param message input message
* @return instance of {@link FunctionRoutingResult} containing the result of the routing computation
*/
default String routingResult(Message<?> message) {
return (String) message.getHeaders().get(FunctionProperties.FUNCTION_DEFINITION);
}
}