Java tutorial
/* * Copyright 2002-2018 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 org.springframework.lang.Nullable; import org.springframework.messaging.Message; import org.springframework.messaging.MessageChannel; import org.springframework.messaging.MessageHandler; /** * An extension of {@link ChannelInterceptor} with callbacks to intercept the * asynchronous sending of a {@link org.springframework.messaging.Message} to * a specific subscriber through an {@link java.util.concurrent.Executor}. * Supported on {@link org.springframework.messaging.MessageChannel} * implementations that can be configured with an {@code Executor}. * * @author Rossen Stoyanchev * @since 4.1 * @see Message * @see MessageChannel * @see MessageHandler */ public interface ExecutorChannelInterceptor extends ChannelInterceptor { /** * Invoked inside the {@link Runnable} submitted to the Executor just before * calling the target MessageHandler to handle the message. Allows for * modification of the Message if necessary or when {@code null} is returned * the MessageHandler is not invoked. * @param message the message to be handled * @param channel the channel on which the message was sent to * @param handler the target handler to handle the message * @return the input message, or a new instance, or {@code null} */ @Nullable default Message<?> beforeHandle(Message<?> message, MessageChannel channel, MessageHandler handler) { return message; } /** * Invoked inside the {@link Runnable} submitted to the Executor after calling * the target MessageHandler regardless of the outcome (i.e. Exception raised * or not) thus allowing for proper resource cleanup. * <p>Note that this will be invoked only if beforeHandle successfully completed * and returned a Message, i.e. it did not return {@code null}. * @param message the message handled * @param channel the channel on which the message was sent to * @param handler the target handler that handled the message * @param ex any exception that may been raised by the handler */ default void afterMessageHandled(Message<?> message, MessageChannel channel, MessageHandler handler, @Nullable Exception ex) { } }