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86 lines
3.2 KiB
Markdown
86 lines
3.2 KiB
Markdown
# Schedule example
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### 1 启动消费者等待传入的订阅消息
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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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// 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 发送延迟消息
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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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// 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 确认
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您应该会看到消息在其存储时间后大约 10 秒被消耗。
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### 4 延迟消息的使用场景
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例如在电子商务中，如果提交订单，可以发送延迟消息，1小时后可以查看订单状态。 如果订单仍未付款，则可以取消订单并释放库存。
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### 5 使用延迟消息的限制
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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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当前 RocketMQ 不支持任意时间的延迟。 生产者发送延迟消息前需要设置几个固定的延迟级别，分别对应1s到2h的1到18个延迟级，消息消费失败会进入延迟消息队列，消息发送时间与设置的延迟级别和重试次数有关。
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See `SendMessageProcessor.java`
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