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TDMQ for RocketMQ
DocumentationTDMQ for RocketMQRocketMQ 4.xSDK DocumentationAccess over TCPSDK for JavaSending and Receiving Filtered Messages
Sending and Receiving Filtered Messages
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Last updated: 2023-03-28 10:15:45
Sending and Receiving Filtered Messages
Last updated: 2023-03-28 10:15:45
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Overview

This document describes how to use open-source SDK to send and receive filtered messages by using the SDK for Java as an example. You can do so with tags or SQL expressions.

Prerequisites

You have created the required resources. If it is a globally sequential message, you need to create a single-queue topic. For more information, see Resource Creation and Preparation.
You have installed JDK 1.8 or later.
You have installed Maven 2.5 or later.
You have downloaded the demo here or have downloaded one at the GitHub project.
You have learned about the sending and receiving processes of general messages.

Tag-based option

The main code of creating producer and consumer is basically same as that for general messages.
For message production, a message need to be carried with a or more tags when constructing the message body.
For message consumption, a message need to be carried with a tag, an asterisk (*), or multiple tag expressions when being subscribed to.

Step 1. Produce messages

Sending messages

The main code of sending messages is basically same as that for general messages. However, a message is allowed to carry only a tag when constructing the message body.
int totalMessagesToSend = 5;
for (int i = 0; i < totalMessagesToSend; i++) {
    Message msg = new Message(TOPIC_NAME, "Tag1", "Hello RocketMQ.".getBytes(StandardCharsets.UTF_8));
    // Send the message
    SendResult sendResult = producer.send(message);
    System.out.println("sendResult = " + sendResult);
}

Step 2. Consume messages

Subscribing to messages

// Subscribe to all tags when subscribing to a topic
pushConsumer.subscribe(topic_name, "*");

//Subscribe to the specified tags
//pushConsumer.subscribe(TOPIC_NAME, "Tag1");  

// Subscribe to multiple tags
//pushConsumer.subscribe(TOPIC_NAME, "Tag1||Tag2");   
      
// Register a callback implementation class to process messages pulled from the broker
pushConsumer.registerMessageListener((MessageListenerConcurrently) (msgs, context) -> {
          // Message processing logic
          System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);
          // Mark the message as being successfully consumed and return the consumption status
          return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
});
// Start the consumer instance
pushConsumer.start();
Parameter
Description
topic_name
Topic name, which can be copied under the Topic tab on the Cluster page in the console.
"*"
If the subscription expression is left empty or specified as asterisk (*), all messages are subscribed to. tag1 || tag2 || tag3 means subscribing to multiple types of tags.
Note
Above is a brief introduction to message publishing and subscription. For more information, see GitHub Demo or official RocketMQ documentation.

SQL expression-based option

The main code of creating producer and consumer is basically same as that for general messages.
For message production, a message need to be carried with user-defined properties when constructing the message body.
For message consumption, a message need to be carried with corresponding SQL expression when being subscribed to.

Step 1. Produce messages

The main code of sending messages is basically same as that for general messages. However, a message is allowed to carry multiple user-defined properties when constructing the message body.
int totalMessagesToSend = 5;
for (int i = 0; i < totalMessagesToSend; i++) {
    Message msg = new Message(TOPIC_NAME,"Hello RocketMQ.".getBytes(StandardCharsets.UTF_8));
    msg.putUserProperty("key1","value1");
    // Send the message
    SendResult sendResult = producer.send(message);
    System.out.println("sendResult = " + sendResult);
}

Step 2. Consume messages

The main code of consuming messages is basically same as that for general messages. However, a message need to be carried with corresponding SQL expression when being subscribed to.
pushConsumer.subscribe(TOPIC_NAME, MessageSelector.bySql("True"));  

// Subscribe to single-key SQL expression when subscribing to a topic
//pushConsumer.subscribe(TOPIC_NAME,    MessageSelector.bySql("key1 IS NOT NULL AND key1='value1'"));

//Subscribe to multiple properties
//pushConsumer.subscribe(TOPIC_NAME,    MessageSelector.bySql("key1 IS NOT NULL AND key2 IS NOT NULL  AND key1='value1' AND key2='value2'"));
      
// Register a callback implementation class to process messages pulled from the broker
pushConsumer.registerMessageListener((MessageListenerConcurrently) (msgs, context) -> {
          // Message processing logic
          System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);
          // Mark the message as being successfully consumed and return the consumption status
          return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
});
// Start the consumer instance
pushConsumer.start();
Note
Above is a brief introduction to message publishing and subscription. For more information, see GitHub Demo or official RocketMQ documentation.


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