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Dios314
90 lines
3.5 KiB
Markdown
90 lines
3.5 KiB
Markdown
# Schedule example
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### 1 Start consumer to wait for incoming subscribed messages
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```java
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import org.apache.rocketmq.client.consumer.DefaultMQPushConsumer;
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import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
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import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
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import org.apache.rocketmq.client.consumer.listener.MessageListenerConcurrently;
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import org.apache.rocketmq.common.message.MessageExt;
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import java.util.List;
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public class ScheduledMessageConsumer {
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public static void main(String[] args) throws Exception {
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// Instantiate message consumer
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DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("ExampleConsumer");
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// Specify name server addresses
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consumer.setNamesrvAddr("localhost:9876");
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// Subscribe topics
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consumer.subscribe("TestTopic", "*");
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// Register message listener
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consumer.registerMessageListener(new MessageListenerConcurrently() {
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@Override
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public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> messages, ConsumeConcurrentlyContext context) {
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for (MessageExt message : messages) {
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// Print approximate delay time period
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System.out.println("Receive message[msgId=" + message.getMsgId() + "] "
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+ (System.currentTimeMillis() - message.getStoreTimestamp()) + "ms later");
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}
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return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
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}
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});
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// Launch consumer
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consumer.start();
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}
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}
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```
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### 2 Send scheduled messages
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```java
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import org.apache.rocketmq.client.producer.DefaultMQProducer;
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import org.apache.rocketmq.common.message.Message;
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public class ScheduledMessageProducer {
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public static void main(String[] args) throws Exception {
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// Instantiate a producer to send scheduled messages
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DefaultMQProducer producer = new DefaultMQProducer("ExampleProducerGroup");
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// Specify name server addresses
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producer.setNamesrvAddr("localhost:9876");
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// Launch producer
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producer.start();
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int totalMessagesToSend = 100;
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for (int i = 0; i < totalMessagesToSend; i++) {
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Message message = new Message("TestTopic", ("Hello scheduled message " + i).getBytes());
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// This message will be delivered to consumer 10 seconds later.
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message.setDelayTimeLevel(3);
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// Send the message
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producer.send(message);
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}
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// Shutdown producer after use.
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producer.shutdown();
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}
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}
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```
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### 3 Verification
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You should see messages are consumed about 10 seconds later than their storing time.
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### 4 Use scenarios for scheduled messages
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For example, in e-commerce, if an order is submitted, a delay message can be sent, and the status of the order can be checked after 1 hour. If the order is still unpaid, the order can be cancelled and the inventory released.
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### 5 Restrictions on the use of scheduled messages
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```java
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// org/apache/rocketmq/store/config/MessageStoreConfig.java
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private String messageDelayLevel = "1s 5s 10s 30s 1m 2m 3m 4m 5m 6m 7m 8m 9m 10m 20m 30m 1h 2h";
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```
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Nowadays RocketMq does not support any time delay. It needs to set several fixed delay levels, which correspond to level 1 to 18 from 1s to 2h. Message consumption failure will enter the delay message queue. Message sending time is related to the set delay level and the number of retries.
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See `SendMessageProcessor.java`
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