《Apache RocketMQ用户指南》之定时消息示例，

import org.apache.rocketmq.client.consumer.DefaultMQPushConsumer;
 import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
 import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
 import org.apache.rocketmq.client.consumer.listener.MessageListenerConcurrently;
 import org.apache.rocketmq.common.message.MessageExt;
 import java.util.List;
    
 public class ScheduledMessageConsumer {
    
     public static void main(String[] args) throws Exception {
         // Instantiate message consumer
         DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("ExampleConsumer");
         // Subscribe topics
         consumer.subscribe("TestTopic", "*");
         // Register message listener
         consumer.registerMessageListener(new MessageListenerConcurrently() {
             @Override
             public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> messages, ConsumeConcurrentlyContext context) {
                 for (MessageExt message : messages) {
                     // Print approximate delay time period
                     System.out.println("Receive message[msgId=" + message.getMsgId() + "] "
                             + (System.currentTimeMillis() - message.getStoreTimestamp()) + "ms later");
                 }
                 return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
             }
         });
         // Launch consumer
         consumer.start();
     }
 }

import org.apache.rocketmq.client.producer.DefaultMQProducer;
 import org.apache.rocketmq.common.message.Message;
    
 public class ScheduledMessageProducer {
    
     public static void main(String[] args) throws Exception {
         // Instantiate a producer to send scheduled messages
         DefaultMQProducer producer = new DefaultMQProducer("ExampleProducerGroup");
         // Launch producer
         producer.start();
         int totalMessagesToSend = 100;
         for (int i = 0; i < totalMessagesToSend; i++) {
             Message message = new Message("TestTopic", ("Hello scheduled message " + i).getBytes());
             // This message will be delivered to consumer 10 seconds later.
             message.setDelayTimeLevel(3);
             // Send the message
             producer.send(message);
         }
    
         // Shutdown producer after use.
         producer.shutdown();
     }
        
 }