001/* 002 * Copyright 2002-2018 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.messaging.support; 018 019import org.springframework.lang.Nullable; 020import org.springframework.messaging.Message; 021import org.springframework.messaging.MessageChannel; 022 023/** 024 * Interface for interceptors that are able to view and/or modify the 025 * {@link Message Messages} being sent-to and/or received-from a 026 * {@link MessageChannel}. 027 * 028 * @author Mark Fisher 029 * @author Rossen Stoyanchev 030 * @since 4.0 031 * @see Message 032 * @see MessageChannel 033 */ 034public interface ChannelInterceptor { 035 036 /** 037 * Invoked before the Message is actually sent to the channel. 038 * This allows for modification of the Message if necessary. 039 * If this method returns {@code null} then the actual 040 * send invocation will not occur. 041 */ 042 @Nullable 043 default Message<?> preSend(Message<?> message, MessageChannel channel) { 044 return message; 045 } 046 047 /** 048 * Invoked immediately after the send invocation. The boolean 049 * value argument represents the return value of that invocation. 050 */ 051 default void postSend(Message<?> message, MessageChannel channel, boolean sent) { 052 } 053 054 /** 055 * Invoked after the completion of a send regardless of any exception that 056 * have been raised thus allowing for proper resource cleanup. 057 * <p>Note that this will be invoked only if {@link #preSend} successfully 058 * completed and returned a Message, i.e. it did not return {@code null}. 059 * @since 4.1 060 */ 061 default void afterSendCompletion( 062 Message<?> message, MessageChannel channel, boolean sent, @Nullable Exception ex) { 063 } 064 065 /** 066 * Invoked as soon as receive is called and before a Message is 067 * actually retrieved. If the return value is 'false', then no 068 * Message will be retrieved. This only applies to PollableChannels. 069 */ 070 default boolean preReceive(MessageChannel channel) { 071 return true; 072 } 073 074 /** 075 * Invoked immediately after a Message has been retrieved but before 076 * it is returned to the caller. The Message may be modified if 077 * necessary; {@code null} aborts further interceptor invocations. 078 * This only applies to PollableChannels. 079 */ 080 @Nullable 081 default Message<?> postReceive(Message<?> message, MessageChannel channel) { 082 return message; 083 } 084 085 /** 086 * Invoked after the completion of a receive regardless of any exception that 087 * have been raised thus allowing for proper resource cleanup. 088 * <p>Note that this will be invoked only if {@link #preReceive} successfully 089 * completed and returned {@code true}. 090 * @since 4.1 091 */ 092 default void afterReceiveCompletion(@Nullable Message<?> message, MessageChannel channel, 093 @Nullable Exception ex) { 094 } 095 096}