在消息队列（MQ）中实现延迟队列有几种常见方法。以下是两种常见的实现方式：

1. 使用死信队列（DLQ）

这种方法利用了消息的死信特性：

1. 消息过期时间：为消息设置一个TTL（Time-To-Live）。
2. 死信交换器（DLX）：当消息在队列中过期后，将其转发到一个专门的死信交换器。
3. 延迟消费：在死信交换器中将消息路由到延迟队列，消费者从延迟队列中消费消息。

适用场景：适合需要较长延迟的场景。

优点：

• 简单易用，不需要额外的插件或复杂配置。

缺点：

• 精度可能不高，取决于TTL设置和消息处理时间。

2. 使用定时队列插件（如RabbitMQ的延迟插件）

通过RabbitMQ的延迟插件可以实现：

1. 消息头设置：发送消息时，通过设置消息头的x-delay属性来指定延迟时间。
2. 延迟交换器：消息被投递到延迟交换器，延迟时间到达后再转发到目标队列。

适用场景：需要精确控制延迟时间的场景。

优点：

• 支持毫秒级别的延迟精度。
• 配置简单，支持动态调节延迟时间。

缺点：

• 需要安装额外的插件，增加了系统复杂性。

插件地址：

链接：https://pan.baidu.com/s/1IUMEk832ymPR6aqqRj0Y_g?pwd=04gk 
提取码：04gk

下面是两种方法的代码示例：

1.使用死信队列

生产者：

import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.Channel;import java.util.HashMap;
import java.util.Map;public class ProducerDLQ {private final static String NORMAL_QUEUE = "normal_queue";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {// 设置死信队列参数Map<String, Object> args = new HashMap<>();args.put("x-dead-letter-exchange", "dlx_exchange");args.put("x-message-ttl", 10000); // 消息存活时间，单位为毫秒channel.queueDeclare(NORMAL_QUEUE, false, false, false, args);String message = "Hello World!";channel.basicPublish("", NORMAL_QUEUE, null, message.getBytes());System.out.println(" [x] Sent '" + message + "'");}}
}

消费者：

 

import com.rabbitmq.client.*;public class ConsumerDLQ {private final static String DLX_QUEUE = "dlx_queue";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {channel.exchangeDeclare("dlx_exchange", "direct");channel.queueDeclare(DLX_QUEUE, false, false, false, null);channel.queueBind(DLX_QUEUE, "dlx_exchange", "");DeliverCallback deliverCallback = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [x] Received '" + message + "'");};channel.basicConsume(DLX_QUEUE, true, deliverCallback, consumerTag -> { });}}
}

2.使用延迟插件

插件地址文章首部给出

import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.AMQP;import java.util.HashMap;
import java.util.Map;public class ProducerDelay {private final static String DELAYED_EXCHANGE = "delayed_exchange";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {// 设置延迟交换器类型Map<String, Object> args = new HashMap<>();args.put("x-delayed-type", "direct");channel.exchangeDeclare(DELAYED_EXCHANGE, "x-delayed-message", false, false, args);String message = "Hello World!";Map<String, Object> headers = new HashMap<>();headers.put("x-delay", 10000); // 延迟时间AMQP.BasicProperties.Builder props = new AMQP.BasicProperties.Builder();props.headers(headers);channel.basicPublish(DELAYED_EXCHANGE, "", props.build(), message.getBytes());System.out.println(" [x] Sent '" + message + "' with delay");}}
}

消费者

import com.rabbitmq.client.*;public class ConsumerDelay {private final static String DELAYED_QUEUE = "delayed_queue";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {channel.queueDeclare(DELAYED_QUEUE, false, false, false, null);channel.queueBind(DELAYED_QUEUE, "delayed_exchange", "");DeliverCallback deliverCallback = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [x] Received '" + message + "'");};channel.basicConsume(DELAYED_QUEUE, true, deliverCallback, consumerTag -> { });}}
}