Can you explain the working principle of the Pull model in message exchange systems?

In the Pull model, the client independently requests messages from the server or message broker when it is ready to process them. That is, the client periodically or upon an event contacts the messaging system and "pulls" new data.

Working principle:

• The client sends a request to receive messages.
• The server returns available messages (if any).
• The client processes the received messages.
• If necessary, the client repeats the request later.

This approach allows controlling the load on the client and processing messages at a convenient time. Unlike the Push model, where the server sends messages to the client itself, Pull gives the client more control and reduces the risk of overload.

Example in Java (simplified):

while (true) {
    List<Message> messages = messageQueue.pullMessages(); // request messages
    for (Message msg : messages) {
        process(msg);
    }
    Thread.sleep(1000); // pause before the next request
}