【RabbitMQ】六、rabbitmq生產者的消息確認

經過Publisher Confirms and Returns機制，生產者能夠判斷消息是否發送到了exchange及queue，而經過消費者確認機制，Rabbitmq能夠決定是否重發消息給消費者，以保證消息被處理。

1.什麼是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)對發佈者(publishers)的確認被稱做發佈者確認(publisher confirms)，這種機制是Rabbitmq對標準Amqp協議的擴展。所以經過這種機制能夠確認消息是否發送給了目標。

2.如何經過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

經過Spring amqp文檔能夠看到，要使用這種機制須要將Template模版的設publisherConfirms 或publisherReturns 屬性設置爲true，此外ConnectionFactory要配置爲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);

    @Override
    public 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);

    @Override
    public 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：

若是消息沒有到exchange,則confirm回調,ack=false

若是消息到達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,不然不回回調,消息就丟了)