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title: “Schedule example” permalink: /docs/schedule-example/ excerpt: “How to use schedule component to reduce pull in RocketMQ.” modified: 2017-04-24T15:01:43-04:00

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What is scheduled message?

Scheduled messages differ from normal messages in that they won't be delivered until a provided time later.

Application

1. Start consumer to wait for incoming subscribed messages

   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();
       }
   }
   

2. Send scheduled messages

   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();
       }
   
   }
   

3. Verification

   You should see messages are consumed about 10 seconds later than their storing time.