TTL

• TTL 是Time To Live 的缩写。也就是生存时间
• RabbitMQ支持消息的过期时间，在消息发送时可以进行指定。
• RabbitMQ支持队列的过期时间，从消息入队列开始计算，只要超过了队列的超时时间配置，那么消息会自动的清除，

死信队列

死信队列： DLX ,Dead-Letter-Exchange

• 利用DLX,当消息在一个队列中变成死信（dead message）之后，它能被重新publish到另一个Exchange.这个Exchange就是DLX

消息变成死信有以下几种情况

• 消息被拒绝（basic.reject/ basic.nack）并且 requeue=false(没有被重回队列)
• 消息TTL过期
• 队列到达最大长度

描述

• DLX也是一个正常的Exchange,和一般的Exchange没有区别，它能在任何的队列上被指定，实际上就是设置某个队列的属性。
• 当这个队列中有死信时，RabbitMQ就会自动的将这个消息重新发布到设置的Exchange上去，进而被路由到另一个队列。
• 可以监听这个队列中消息做相应的处理。这个特性可以弥补RabbitMQ 3.0前支持的immediate参数功能。

死信队列设置

• 首先需要设置死信队列的Exchange和queue.然后进行绑定：

  • Exchange: dlx.exchange
  • Queue: dlx.queue
  • RoutingKey: #

• 然后我们正常声明交换机，队列，绑定，只不过我们需要在队列加上一个参数即可：arguments.put("x-dead-letter-exchange","dlx.exchange");

• 这样消息在过期，requeue(重回队列) ，队列在达到最大长度时，消息就可以直接路由到死信队列！

/**
 * 死信队列
 *
 * @author yangHX
 * createTime  2019/3/28 22:51
 */
public class Producer {

    public static void main(String[] args) throws IOException, TimeoutException {
        ConnectionFactory connectionFactory = RabbitMqUtil.getConnectionFactory();
        Connection connection = connectionFactory.newConnection();
        Channel channel = connection.createChannel();

        String exchangeName = "test_dlx_exchange";
        String routingKey = "dlx.sve";
        String msg = "Hello RabbitMQ DLX Message";

        for (int i = 0; i < 5; i++) {
            AMQP.BasicProperties build = new AMQP.BasicProperties().builder()
                    .deliveryMode(2)
                    .contentEncoding("UTF-8")
                    .expiration("10000")
                    .build();
            channel.basicPublish(exchangeName, routingKey, build, msg.getBytes());
        }
    }
}


/**
 * 死信队列
 *
 * @author yangHX
 * createTime  2019/3/28 22:55
 */
public class Consumer {

    public static void main(String[] args) throws IOException, TimeoutException {
        ConnectionFactory connectionFactory = RabbitMqUtil.getConnectionFactory();
        Connection connection = connectionFactory.newConnection();
        Channel channel = connection.createChannel();

        //这就是一个普通的交换机，和队列 以及路由
        String exchangeName = "test_dlx_exchange";
        String routingKey = "dlx.#";
        String queueName = "test_dlx_queue";

        channel.exchangeDeclare(exchangeName, "topic", true, false, null);

        HashMap<String, Object> arguments = new HashMap<>();
        arguments.put("x-dead-letter-exchange", "dlx.exchange");

        //这个arguments属性，要设置到声明队列上
        channel.queueDeclare(queueName, true, false, false, arguments);
        channel.queueBind(queueName, exchangeName, routingKey);

        //要进行死信队列的声明
        channel.exchangeDeclare("dlx.exchange", "topic", true, false, null);
        channel.queueDeclare("dlx.queue", true, false, false, null);
        channel.queueBind("dlx.queue", "dlx.exchange", "#");

        channel.basicConsume(queueName, true, new MyConsumer(channel));


    }
}




/**
 * @author yangHX
 * createTime  2019/3/28 23:02
 */
public class MyConsumer extends DefaultConsumer {
    Channel channel;

    /**
     * Constructs a new instance and records its association to the passed-in channel.
     *
     * @param channel the channel to which this consumer is attached
     */
    public MyConsumer(Channel channel) {
        super(channel);
        this.channel = channel;
    }

    @Override
    public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
        System.err.println("-----------consume message----------");
        System.err.println("consumerTag: " + consumerTag);
        System.err.println("envelope: " + envelope);
        System.err.println("properties: " + properties);
        System.err.println("body: " + new String(body));
    }
}

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