How to use Java to develop a distributed messaging middleware application based on RocketMQ

How to use Java to develop a distributed messaging middleware application based on RocketMQ

Introduction:
With the rapid development of the Internet industry, distributed systems have become increasingly common. As one of the commonly used components in distributed systems, message middleware plays an important role in connecting various distributed components, achieving decoupling, and ensuring data consistency. This article will introduce how to use Java to develop a distributed messaging middleware application based on RocketMQ, aiming to help readers understand and master how to use RocketMQ for distributed messaging.

1. Preparation

1. Install RocketMQ and start NameServer and Broker
   Download address: http://rocketmq.apache.org/
2. Create Maven Project
   Create a new Maven project in the IDE and add dependencies as follows:

<dependency>
    <groupId>org.apache.rocketmq</groupId>
    <artifactId>rocketmq-client</artifactId>
    <version>4.8.0</version>
</dependency>

2. Send message

1. Create producer

   import org.apache.rocketmq.client.producer.DefaultMQProducer;
   import org.apache.rocketmq.common.message.Message;
   import org.apache.rocketmq.remoting.common.RemotingHelper;
   
   public class Producer {
       public static void main(String[] args) throws Exception {
           DefaultMQProducer producer = new DefaultMQProducer("producerGroup");
           producer.setNamesrvAddr("localhost:9876");
           producer.start();
   
           Message message = new Message("TopicTest", "TagA", "Hello RocketMQ".getBytes(RemotingHelper.DEFAULT_CHARSET));
           producer.send(message);
           System.out.println("发送消息成功");
   
           producer.shutdown();
       }
   }

   Create a class named Producer, create a DefaultMQProducer instance in the main method, and set the NameServer address. Next, create a Message instance and specify the subject, label, and message content to be sent. Call the producer.send(message) method to send the message, and finally close the producer.

2. Run the Producer
   Run the main method of the Producer class. If everything is configured correctly, you will see the output of "Message sent successfully" on the console.

3. Receive messages

1. Create a consumer

   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 Consumer {
       public static void main(String[] args) throws Exception {
           DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("consumerGroup");
           consumer.setNamesrvAddr("localhost:9876");
           consumer.subscribe("TopicTest", "*");
   
           consumer.registerMessageListener(new MessageListenerConcurrently() {
               @Override
               public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> list, ConsumeConcurrentlyContext consumeConcurrentlyContext) {
                   for (MessageExt messageExt : list) {
                       System.out.println("接收到消息：" + new String(messageExt.getBody()));
                   }
                   return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
               }
           });
   
           consumer.start();
           System.out.println("消费者启动");
       }
   }

   Create a class named Consumer and create a DefaultMQPushConsumer in the main method instance and set the NameServer address. Next, subscribe to the topics and tags you want to consume by calling the consumer.subscribe method. Then, use the registerMessageListener method of the Consumer object to register a message listener and execute business logic when the message arrives. Finally, start the consumer.

2. Run the Consumer
   Run the main method of the Consumer class. If everything is configured correctly, you will see the output of "Consumer Started" on the console and be able to receive the messages sent by the producer. information.

4. Summary
Through the introduction of this article, we have learned how to use Java to develop a distributed messaging middleware application based on RocketMQ. We learned how to send and receive messages and were given specific code examples. Of course, in actual applications, more functions such as handling exceptions and setting message delays need to be more detailed. I hope this article can help you get started with RocketMQ and apply message middleware technology in actual projects to improve the scalability and stability of the system.

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