通過Publisher Confirms and Returns機制，生產者可以判斷消息是否發送到了exchange及queue，而通過消費者確認機制，Rabbitmq可以決定是否重發消息給消費者，以保證消息被處理。

1.什么是Publisher Confirms and Returns？

Delivery processing acknowledgements from consumers to RabbitMQ are known as acknowledgements in AMQP 0-9-1 parlance; broker acknowledgements to publishers are a protocol extension called publisher confirms.?
地址：http://www.rabbitmq.com/confirms.html

根據RabbitMq官網定義，rabbitmq代理(broker)對發布者(publishers)的確認被稱作發布者確認(publisher confirms)，這種機制是Rabbitmq對標準Amqp協議的擴展。因此通過這種機制可以確認消息是否發送給了目標。

2.如何通過Spring amqp來使用Publisher Confirms and Returns機制？

Confirmed and returned messages are supported by setting the CachingConnectionFactory’s publisherConfirms and publisherReturns properties to ‘true’ respectively.When these options are set, Channel s created by the factory are wrapped in an PublisherCallbackChannel, which is used to facilitate the callbacks. When such a channel is obtained, the client can register a PublisherCallbackChannel.Listener with the Channel. The PublisherCallbackChannel implementation contains logic to route a confirm/return to the appropriate listener. These features are explained further in the following sections.?
http://docs.spring.io/spring-amqp/docs/1.6.3.RELEASE/reference/html/_reference.html#cf-pub-conf-ret

通過Spring amqp文檔可以看到，要使用這種機制需要將Template模版的設publisherConfirms 或publisherReturns 屬性設置為true，此外ConnectionFactory要配置為CachingConnectionFactory。

<bean id="connectionFactory"class="org.springframework.amqp.rabbit.connection.CachingConnectionFactory"><property name="host" value="192.168.2.133" /><property name="port" value="5672" /><property name="username" value="sun" /><property name="password" value="123456" /><property name="publisherConfirms" value="true" /><property name="publisherReturns" value="true" /></bean>

2.1 ConfirmCallback的使用及觸發的一種場景

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.amqp.rabbit.support.CorrelationData;
import org.springframework.stereotype.Service;/*** @author wangzhongqiu*         Created on 2017/10/31.* @description:繼承RabbitTemplate.ConfirmCallback,消息確認監聽器*/
@Service
public class ConfirmCallBackListener implements RabbitTemplate.ConfirmCallback {private Logger log = LoggerFactory.getLogger(CommonProducer.class);@Overridepublic void confirm(CorrelationData correlationData, boolean ack, String cause) {log.info("收到回調，成功發送到broker");}
}

2.2 ReturnCallback的使用及觸發的一種場景

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.amqp.core.Message;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.stereotype.Service;/*** @author wangzhongqiu*         Created on 2017/10/31.* @description:繼承RabbitTemplate.ReturnCallback,消息發送失敗返回監聽器*/
@Service
public class ReturnCallBackListener implements RabbitTemplate.ReturnCallback {private Logger log = LoggerFactory.getLogger(CommonProducer.class);@Overridepublic void returnedMessage(Message message, int replyCode, String replyText, String exchange, String routingKey) {log.info("收到回調");log.info("return--message:" + new String(message.getBody()) + ",replyCode:" + replyCode + ",replyText:" + replyText + ",exchange:" + exchange + ",routingKey:" + routingKey);}
}

使用場景：

如果消息沒有到exchange,則confirm回調,ack=false

如果消息到達exchange,則confirm回調,ack=true

exchange到queue成功,則不回調return

exchange到queue失敗,則回調return(需設置mandatory=true,否則不回回調,消息就丟了)