12. Priority queue and inert queue

Priority queue

How to add priority

• choice Maximum priority, Value specifying priority , Set the range to 0-255, If the value is 10, So that is 0-10, Maximum not exceeding 255

Code form

Map<String,Object> params  = new HashMap<>();
params.put("x-max-priority",10);
channel.queueDeclare("hello",true,false,false,params);

Case presentation

Producer code

/** *  Priority queue   producer  */
public class PriorityProducer {
    
    public static void main(String[] args) throws IOException {
    
        Channel channel = RabbitUtil.getChannel();
        AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().priority(5).build();

        for (int i = 0; i < 10; i++) {
    
            String message = "info"+ i;
            if (i==5){
    
                channel.basicPublish("","hello",properties,message.getBytes(StandardCharsets.UTF_8));
            }else {
    
                channel.basicPublish("","hello",null,message.getBytes(StandardCharsets.UTF_8));
            }
        }
        System.out.println(" Send message complete ");
    }
}

Consumer code

/** *  Priority queue   consumer  */
public class PriorityConsumer {
    

    public static void main(String[] args) throws IOException {
    
        Channel channel = RabbitUtil.getChannel();
        Map<String,Object> params  = new HashMap<>();
        params.put("x-max-priority",10);
        channel.queueDeclare("hello",true,false,false,params);
        System.out.println(" Consumers start waiting for consumption ...");
        DeliverCallback deliverCallback = (consumerTag, message) -> {
    
            String received = new String( message.getBody());
            System.out.println(" Message received ："+received);
        };
        channel.basicConsume("hello",true,deliverCallback,consumerTag -> {
    
            System.out.println(" Called when the consumer cannot consume the message , If the queue is deleted ");
        });
    }
}

result

• Start the producer first , Then start the consumer , Find out info5 Be consumed first
• If you start the consumer first , Restart producer , Because the processing speed is fast enough , There is no message stack in the queue , So execute in order

Lazy queue

Lazy queues store messages to disk as much as possible , When consumers consume the corresponding message, it will be loaded into memory , An important design goal is to support longer queues , That is, support more message storage

When messages cannot be consumed for a long time due to various reasons, resulting in accumulation , Inert queues are necessary

There are two modes of queues ：default and lazy. have access to x-queue-mode To set the mode of the queue , The value is default and lazy.

Declaration of inert queue

Map<String,Object> params = new HashMap();
params.put("x-queue-mode","lazy");
channel.queueDeclare("hello",false,false,false,params);