RabbitMQ学习之延时队列

在实际的业务中我们会遇见生产者产生的消息，不立即消费，而是延时一段时间在消费。RabbitMQ本身没有直接支持延迟队列功能，但是我们可以根据其特性Per-Queue Message TTL和 Dead Letter Exchanges实现延时队列。也可以通过改特性设置消息的优先级。

1.Per-Queue Message TTL
RabbitMQ可以针对消息和队列设置TTL（过期时间）。队列中的消息过期时间(Time To Live, TTL)有两种方法可以设置。第一种方法是通过队列属性设置，队列中所有消息都有相同的过期时间。第二种方法是对消息进行单独设置，每条消息TTL可以不同。如果上述两种方法同时使用，则消息的过期时间以两者之间TTL较小的那个数值为准。消息在队列的生存时间一旦超过设置的TTL值，就成为dead message,消费者将无法再收到该消息。
2.Dead Letter Exchanges
当消息在一个队列中变成死信后，它能被重新publish到另一个Exchange。消息变成Dead Letter一向有以下几种情况：
消息被拒绝（basic.reject or basic.nack）并且requeue=false
消息TTL过期
队列达到最大长度
实际上就是设置某个队列的属性，当这个队列中有Dead Letter时，RabbitMQ就会自动的将这个消息重新发布到设置的Exchange中去，进而被路由到另一个队列，publish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 3.0.0以前支持的immediate参数中的向publish确认的功能。

一、在队列上设置TTL

1.建立delay.exchange

这里Internal设置为NO，否则将无法接受dead letter，YES表示这个exchange不可以被client用来推送消息，仅用来进行exchange和exchange之间的绑定。

2.建立延时队列(delay queue)

如上配置延时5min队列(x-message-ttl=300000)

x-max-length:最大积压的消息个数，可以根据自己的实际情况设置，超过限制消息不会丢失，会立即转向delay.exchange进行投递

x-dead-letter-exchange:设置为刚刚配置好的delay.exchange,消息过期后会通过delay.exchange进行投递

这里不需要配置"dead letter routing key"否则会覆盖掉消息发送时携带的routingkey，导致后面无法路由为刚才配置的delay.exchange

3.配置延时路由规则

需要延时的消息到exchange后先路由到指定的延时队列

1）创建delaysync.exchange通过Routing key将消息路由到延时队列

2.配置delay.exchange 将消息投递到正常的消费队列

配置完成。

下面使用代码测试一下：

生产者：

package cn.slimsmart.study.rabbitmq.delayqueue.queue;import java.io.IOException;import com.rabbitmq.client.Channel;import com.rabbitmq.client.Connection;import com.rabbitmq.client.ConnectionFactory;public class Producer {private static String queue_name = "test.queue";public static void main(String[] args) throws IOException {ConnectionFactory factory = new ConnectionFactory();factory.setHost("10.1.199.169");factory.setUsername("admin");factory.setPassword("123456");Connection connection = factory.newConnection();Channel channel = connection.createChannel();// 声明队列channel.queueDeclare(queue_name, true, false, false, null);String message = "hello world!" + System.currentTimeMillis();channel.basicPublish("delaysync.exchange", "deal.message", null, message.getBytes());System.out.println("sent message: " + message + ",date:" + System.currentTimeMillis());// 关闭频道和连接channel.close();connection.close();}}

消费者：

package cn.slimsmart.study.rabbitmq.delayqueue.queue;import com.rabbitmq.client.Channel;import com.rabbitmq.client.Connection;import com.rabbitmq.client.ConnectionFactory;import com.rabbitmq.client.QueueingConsumer;public class Consumer {private static String queue_name = "test.queue";public static void main(String[] args) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("10.1.199.169");factory.setUsername("admin");factory.setPassword("123456");Connection connection = factory.newConnection();Channel channel = connection.createChannel();// 声明队列channel.queueDeclare(queue_name, true, false, false, null);QueueingConsumer consumer = new QueueingConsumer(channel);// 指定消费队列channel.basicConsume(queue_name, true, consumer);while (true) {// nextDelivery是一个阻塞方法（内部实现其实是阻塞队列的take方法）QueueingConsumer.Delivery delivery = consumer.nextDelivery();String message = new String(delivery.getBody());System.out.println("received message:" + message + ",date:" + System.currentTimeMillis());}}}

二、在消息上设置TTL

实现代码：

生产者：

package cn.slimsmart.study.rabbitmq.delayqueue.message;import java.io.IOException;import java.util.HashMap;import com.rabbitmq.client.AMQP;import com.rabbitmq.client.Channel;import com.rabbitmq.client.Connection;import com.rabbitmq.client.ConnectionFactory;public class Producer {private static String queue_name = "message_ttl_queue";public static void main(String[] args) throws IOException {ConnectionFactory factory = new ConnectionFactory();factory.setHost("10.1.199.169");factory.setUsername("admin");factory.setPassword("123456");Connection connection = factory.newConnection();Channel channel = connection.createChannel();HashMap<String, Object> arguments = new HashMap<String, Object>();arguments.put("x-dead-letter-exchange", "amq.direct");arguments.put("x-dead-letter-routing-key", "message_ttl_routingKey");channel.queueDeclare("delay_queue", true, false, false, arguments);// 声明队列channel.queueDeclare(queue_name, true, false, false, null);// 绑定路由channel.queueBind(queue_name, "amq.direct", "message_ttl_routingKey");String message = "hello world!" + System.currentTimeMillis();// 设置延时属性AMQP.BasicProperties.Builder builder = new AMQP.BasicProperties.Builder();// 持久性 non-persistent (1) or persistent (2)AMQP.BasicProperties properties = builder.expiration("300000").deliveryMode(2).build();// routingKey =delay_queue 进行转发channel.basicPublish("", "delay_queue", properties, message.getBytes());System.out.println("sent message: " + message + ",date:" + System.currentTimeMillis());// 关闭频道和连接channel.close();connection.close();}}

消费者：

package cn.slimsmart.study.rabbitmq.delayqueue.message;import java.util.HashMap;import com.rabbitmq.client.Channel;import com.rabbitmq.client.Connection;import com.rabbitmq.client.ConnectionFactory;import com.rabbitmq.client.QueueingConsumer;public class Consumer {private static String queue_name = "message_ttl_queue";public static void main(String[] args) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("10.1.199.169");factory.setUsername("admin");factory.setPassword("123456");Connection connection = factory.newConnection();Channel channel = connection.createChannel();HashMap<String, Object> arguments = new HashMap<String, Object>();arguments.put("x-dead-letter-exchange", "amq.direct");arguments.put("x-dead-letter-routing-key", "message_ttl_routingKey");channel.queueDeclare("delay_queue", true, false, false, arguments);// 声明队列channel.queueDeclare(queue_name, true, false, false, null);// 绑定路由channel.queueBind(queue_name, "amq.direct", "message_ttl_routingKey");QueueingConsumer consumer = new QueueingConsumer(channel);// 指定消费队列channel.basicConsume(queue_name, true, consumer);while (true) {// nextDelivery是一个阻塞方法（内部实现其实是阻塞队列的take方法）QueueingConsumer.Delivery delivery = consumer.nextDelivery();String message = new String(delivery.getBody());System.out.println("received message:" + message + ",date:" + System.currentTimeMillis());}}}

查看资料：

http://www.rabbitmq.com/ttl.html 
http://www.rabbitmq.com/dlx.html 
http://www.rabbitmq.com/maxlength.html
https://www.cloudamqp.com/docs/delayed-messages.html