2.4 RabbitMQ高級特效-消息的ACK與重回隊列

消費端的手工ACK和NACK
消費端進行消費的時候，如果由於業務異常我們可以進行日誌的記錄，然後進行補償。如果由於服務器宕機等嚴重問題，那麼我們就需要手工進行ACK保障消費端消費成功。
消費端的重回隊列
消費端重回隊列是爲了對沒有處理成功的消息，把消息重新會遞給Broker！一般我們在實際應用中，都會關閉重回隊列，也就是設置未False。

自定義消費者代碼

package com.star.movie.ack;

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;

import java.io.IOException;

/**
 * @Description：
 * @author:kaili
 * @Date: 2019-04-22 18:47
 **/
public class MyAckConsumer extends DefaultConsumer {

    private Channel channel ;

    public MyAckConsumer(Channel channel) {
        super(channel);
        this.channel = channel;
    }

    @Override
    public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
        String headerMsg = "num";
        System.err.println("-----------consume message----------");
        System.err.println("body: " + new String(body));
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        if((Integer)properties.getHeaders().get(headerMsg) == 0) {
            channel.basicNack(envelope.getDeliveryTag(), false, true);
        } else {
            channel.basicAck(envelope.getDeliveryTag(), false);
        }
    }
}

消費端的代碼，對隊列中的消息獲取head中的屬性num值，如果num爲0就調用nack方法觀察效果

消費者端代碼

package com.star.movie.ack;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.star.movie.common.Constant;

/**
 * @Description：
 * @author:kaili
 * @Date: 2019-04-22 18:46
 **/
public class AckConsumer {
    public static void main(String[] args) throws Exception{
        Connection connection = Constant.getConnection();
        Channel channel = connection.createChannel();


        String exchangeName = "test_ack_exchange";
        String queueName = "test_ack_queue";
        String routingKey = "ack.#";

        channel.exchangeDeclare(exchangeName, "topic", true, false, null);
        channel.queueDeclare(queueName, true, false, false, null);
        channel.queueBind(queueName, exchangeName, routingKey);

        // 手工簽收 必須要關閉 autoAck = false
        channel.basicConsume(queueName, false, new MyAckConsumer(channel));
    }
}

手工簽收 必須要關閉 autoAck = false

生產者代碼

package com.star.movie.ack;

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.star.movie.common.Constant;

import java.util.HashMap;
import java.util.Map;

/**
 * @Description：
 * @author:kaili
 * @Date: 2019-04-22 18:45
 **/
public class AckProducer {
    public static void main(String[] args) throws Exception{
        Connection connection = Constant.getConnection();
        Channel channel = connection.createChannel();
        String exchange = "test_ack_exchange";
        String routingKey = "ack.save";
        for(int i =0; i<5; i ++){
            Map<String, Object> headers = new HashMap<String, Object>();
            headers.put("num", i);
            AMQP.BasicProperties properties = new AMQP.BasicProperties.Builder()
                    .deliveryMode(2)
                    .contentEncoding("UTF-8")
                    .headers(headers)
                    .build();
            String msg = "Hello RabbitMQ ACK Message " + i;
            channel.basicPublish(exchange, routingKey, true, properties, msg.getBytes());
        }
    }
}

step 1 啓動消費者端代碼
生成類型爲topic的交換機test_ack_exchange，綁定test_ack_queue隊列，綁定健爲ack.#

step 2 啓動生產者端代碼

觀察消費者端控制檯打印的信息：

-----------consume message----------
body: Hello RabbitMQ ACK Message 0
-----------consume message----------
body: Hello RabbitMQ ACK Message 1
-----------consume message----------
body: Hello RabbitMQ ACK Message 2
-----------consume message----------
body: Hello RabbitMQ ACK Message 3
-----------consume message----------
body: Hello RabbitMQ ACK Message 4
-----------consume message----------
body: Hello RabbitMQ ACK Message 0
-----------consume message----------
body: Hello RabbitMQ ACK Message 0
-----------consume message----------
body: Hello RabbitMQ ACK Message 0
-----------consume message----------
body: Hello RabbitMQ ACK Message 0

一直在消費head中num爲0的消息，因爲這條消息使用的是nack，並且將消息重回隊列了，所以會這樣一直消費。

step 3關閉消費者端代碼
觀察test_ack_queue隊列

該隊列中還有一條消息待消費，正是我們讓它重回隊列的那條消息

step 4 將重回隊列修改爲false
修改自定義消費者中的代碼

channel.basicNack(envelope.getDeliveryTag(), false, false);

啓動生產者代碼，然後啓動消費者代碼，觀察消費者端的控制檯消息

-----------consume message----------
body: Hello RabbitMQ ACK Message 0
-----------consume message----------
body: Hello RabbitMQ ACK Message 0
-----------consume message----------
body: Hello RabbitMQ ACK Message 1
-----------consume message----------
body: Hello RabbitMQ ACK Message 2
-----------consume message----------
body: Hello RabbitMQ ACK Message 3
-----------consume message----------
body: Hello RabbitMQ ACK Message 4

num爲0的消息消費後未重回Broker