死信队列用于存储过期的消息和消费失败的消息。当消费者从正常队列移除后进入到死信队列。
1:消息变成死信 一 般是由于以下3种情况:
1 :消息被拒绝 (Basic.Reject/Basic .Nack),井且设置 requeue 参数为 false;
// 创建队列消费者
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");
System.out.println("消费者读取:" + message + "失败");
// requeue为true 表示 拒绝消息后马上从队列中移除消息
channel.basicNack(envelope.getDeliveryTag(),true,false);
}
};
2 :消息过期
// 发送消息时设置过期时间为1秒 如果此时消费者没有开启一秒后进入死信队列
AMQP.BasicProperties basicProperties = MessageProperties.PERSISTENT_TEXT_PLAIN;
AMQP.BasicProperties props = new AMQP.BasicProperties
.Builder()
.deliveryMode(2)
.expiration("1000")
.build(); // AMQP.BasicProperties
for (int i = 0; i < 1; i++) {
channel.basicPublish(exchanageName, "com.baidu", props, message.getBytes());
System.out.println("生产者发送:" + message + "'");
}
3:队列达到最大长度。
2:创建死信队列 添加("x-dead-letter-exchange", "dlx.exchange"); dlx.exchange为你自定义的值 此值是死信队列dlx.queue的exchange,死信队列可以任意个只要队列的exchange和x-dead-letter-exchange的值对应。
// 普通队列
String exchangeName = "exchange_topic01";
String routingKey = "com.#";
String queueName = "queue1";
channel.exchangeDeclare(exchangeName, "topic", true, false, null);
Map<String, Object> agruments = new HashMap<String, Object>();
agruments.put("x-dead-letter-exchange", "dlx.exchange");
//这个agruments属性设置到
channel.queueDeclare(queueName, true, false, false, agruments);
channel.queueBind(queueName, exchangeName, routingKey);
//死信队列dlx.exchange 与 上面x-dead-letter-exchange的值对应
String exchangeDxl = "dlx.exchange";
String routingKeyDxl = "#";
String queueNameDxl = "dlx.queue";
channel.exchangeDeclare(exchangeDxl, "topic", true);
channel.queueDeclare(queueNameDxl, true, false, false, null);
channel.queueBind(queueNameDxl, exchangeDxl, routingKeyDxl);