In the previous section, I learned how consumers get messages
So when consumers get the message and find that the message should not be solved by themselves, or an exception occurs during processing, how should they deal with it
This is the message rejection in this section
1, Message reject
There are also two ways to Reject messages: Reject and Nack
Reject can reject only one message at a time, while Nack can reject multiple messages at one time
And either way, you can use the request ID
If it is false, it will not be sent again. Generally, this message will be discarded by RabbitMQ
If true, the message has been redelivered
//Reject (the second parameter here determines whether to redelivery) channel.basicReject(envelope.getDeliveryTag(),true); //Reject in Nack mode (the second parameter determines whether to batch) channel.basicNack(envelope.getDeliveryTag(), false, false);
public class RejectRequeuConsumer {
public static void main(String[] argv) throws Exception {
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("127.0.0.1");
Connection connection = factory.newConnection();
final Channel channel = connection.createChannel();
channel.exchangeDeclare(DirectProducer.EXCHANGE_NAME,"direct");
String queueName = "rejectrequeue";
channel.queueDeclare(queueName,false,false,false,null);
String routekey = "error";
channel.queueBind(queueName,DirectProducer.EXCHANGE_NAME,routekey);
System.out.println("waiting for message........");
/*Declared a consumer*/
final Consumer consumer = new DefaultConsumer(channel){
@Override
public void handleDelivery(String consumerTag,
Envelope envelope,
AMQP.BasicProperties properties,
byte[] body) throws IOException {
try{
String message = new String(body, "UTF-8");
System.out.println("Processing messages");
throw new RuntimeException("Handling exceptions"+message);
}catch (Exception e){
e.printStackTrace();
//TODO Reject (the second parameter here determines whether to redelivery)
//channel.basicReject(envelope.getDeliveryTag(),true);
//Reject in TODO Nack mode (the second parameter determines whether to batch)
channel.basicNack(envelope.getDeliveryTag(), false, false);
}
}
};
/*The consumer officially starts consuming messages on the specified queue*/
channel.basicConsume(queueName,false,consumer);
}
}2, Dead letter exchanger
In the above demonstration, when message rejection is used and request is set to false, the message will be discarded
This method is generally rough and is not recommended
In view of this situation, a dead letter exchanger is proposed to deal with dead messages
public class MainConsumer {
public static void main(String[] argv) throws Exception {
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("127.0.0.1");
Connection connection = factory.newConnection();
final Channel channel = connection.createChannel();
channel.exchangeDeclare(DlxProducer.EXCHANGE_NAME,BuiltinExchangeType.TOPIC);
//TODO binding dead letter exchanger
/*Declare a queue and bind the dead letter exchange*/
String queueName = "dlx_make";
Map<String,Object> args = new HashMap<String,Object>();
args.put("x-dead-letter-exchange", DlxProcessConsumer.DLX_EXCHANGE_NAME);
//TODO dead letter routing key will replace the original routing key of the message
//args.put("x-dead-letter-routing-key", "deal");
channel.queueDeclare(queueName,false,true,false,args);
/*Binding: bind the queue and the switch through the routing key*/
channel.queueBind(queueName,DlxProducer.EXCHANGE_NAME,"#");
System.out.println("waiting for message........");
/*Declared a consumer*/
final Consumer consumer = new DefaultConsumer(channel){
@Override
public void handleDelivery(String consumerTag,
Envelope envelope,
AMQP.BasicProperties properties,
byte[] body) throws IOException {
String message = new String(body, "UTF-8");
//If TODO is zc's message confirmation
if(envelope.getRoutingKey().equals("zc")){
channel.basicAck(envelope.getDeliveryTag(),false);
}else{
//If TODO is rejected by other messages (queue=false), it becomes a dead letter message
channel.basicReject(envelope.getDeliveryTag(),false);
}
}
};
/*The consumer officially starts consuming messages on the specified queue*/
channel.basicConsume(queueName,false,consumer);
}
}Difference between and standby exchanger
1. If the standby switch is the primary switch that cannot route messages, the messages will be routed to the new standby switch, while the dead letter switch receives expired or rejected messages.
2. The standby switch is contacted when declaring the primary switch, while the dead letter switch is contacted when declaring the queue.