死信队列
概念
先从概念解释上搞清楚这个定义，死信，顾名思义就是无法被消费的消息，字面意思可以这样理解，一般来说，producer将消息投递到broker或者直接到queue里了，consumer从queue取出消息进行消费，但某些时候由于特定的原因导致queue中的某些消息无法被消费，这样的消息如果没有后续的处理，就变成了死信，有死信自然就有了死信队列。
应用场景:为了保证订单业务的消息数据不丢失，需要使用到 RabbitMQ 的死信队列机制，当消息消费发生异常时，将消息投入死信队列中.还有比如说: 用户在商城下单成功并点击去支付后在指定时间未支付时自动失效。
死信的来源
消息TTL过期
队列达到最大长度(队列满了，无法再添加数据到 mq 中)
消息被拒绝(basic.reject或basic.nack)并且requeue=false.
代码架构图
消息 TTL 过期
生产者代码
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| public class Producer {
private static final String NORMAL_EXCHANGE = "normal_exchange";
public static void main(String[] argv) throws Exception {
try (Channel channel = RabbitMqUtils.getChannel()) {
channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().expiration("10000").build();
for (int i = 1; i <11 ; i++) {
String message="info"+i;
channel.basicPublish(NORMAL_EXCHANGE, "zhangsan", properties, message.getBytes());
System.out.println("生产者发送消息:"+message);
}
}
}
}
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消费者C1代码(启动之后关闭该消费者 模拟其接收不到消息)
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public class Consumer01 {
private static final String NORMAL_EXCHANGE = "normal_exchange";
private static final String DEAD_EXCHANGE = "dead_exchange";
public static void main(String[] argv) throws Exception {
Channel channel = RabbitUtils.getChannel();
channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
String deadQueue = "dead-queue";
channel.queueDeclare(deadQueue, false, false, false, null);
channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");
Map<String, Object> params = new HashMap<>();
params.put("x-dead-letter-exchange", DEAD_EXCHANGE);
params.put("x-dead-letter-routing-key", "lisi");
String normalQueue = "normal-queue";
channel.queueDeclare(normalQueue, false, false, false, params);
channel.queueBind(normalQueue, NORMAL_EXCHANGE, "zhangsan");
System.out.println("等待接收消息.....");
DeliverCallback deliverCallback = (consumerTag, delivery) -> {
String message = new String(delivery.getBody(), "UTF-8");
System.out.println("Consumer01接收到消息"+message);
};
channel.basicConsume(normalQueue, true, deliverCallback, consumerTag -> { });
}
}
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消费者C2代码(以上步骤完成后 启动C2消费者 它消费死信队列里面的消息)
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| public class Consumer02 {
private static final String DEAD_EXCHANGE = "dead_exchange";
public static void main(String[] argv) throws Exception {
Channel channel = RabbitUtils.getChannel();
channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
String deadQueue = "dead-queue";
channel.queueDeclare(deadQueue, false, false, false, null);
channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");
System.out.println("等待接收死信队列消息.....");
DeliverCallback deliverCallback = (consumerTag, delivery) -> {
String message = new String(delivery.getBody(), "UTF-8");
System.out.println("Consumer02接收死信队列的消息" + message);
};
channel.basicConsume(deadQueue, true, deliverCallback, consumerTag -> { });
}
}
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队列达到最大长度
1、消息生产者代码去掉 TTL 属性
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| public class Producer {
private static final String NORMAL_EXCHANGE = "normal_exchange";
public static void main(String[] argv) throws Exception {
try (Channel channel = RabbitMqUtils.getChannel()) {
channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
for (int i = 1; i <11 ; i++) {
String message="info"+i;
channel.basicPublish(NORMAL_EXCHANGE,"zhangsan",null, message.getBytes());
System.out.println("生产者发送消息:"+message);
}
}
}
}
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2、C1消费者修改以下代码(启动之后关闭该消费者 模拟其接收不到消息)
注意此时需要把原先队列删除 因为参数改变了
3、C2消费者代码不变(启动 C2消费者)
消息被拒
1、消息生产者代码同上生产者一致
2、C1消费者代码(启动之后关闭该消费者 模拟其接收不到消息)
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| public class Consumer01 {
private static final String NORMAL_EXCHANGE = "normal_exchange";
private static final String DEAD_EXCHANGE = "dead_exchange";
public static void main(String[] argv) throws Exception {
Channel channel = RabbitUtils.getChannel();
channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT); channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
String deadQueue = "dead-queue"; channel.queueDeclare(deadQueue, false, false, false, null);
channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");
Map<String, Object> params = new HashMap<>();
params.put("x-dead-letter-exchange", DEAD_EXCHANGE);
params.put("x-dead-letter-routing-key", "lisi");
String normalQueue = "normal-queue";
channel.queueDeclare(normalQueue, false, false, false, params);
channel.queueBind(normalQueue, NORMAL_EXCHANGE, "zhangsan");
System.out.println("等待接收消息.....");
DeliverCallback deliverCallback = (consumerTag, delivery) -> {
String message = new String(delivery.getBody(), "UTF-8");
if(message.equals("info5")){
System.out.println("Consumer01接收到消息" + message + "并拒绝签收该消息");
channel.basicReject(delivery.getEnvelope().getDeliveryTag(), false);
}else {
System.out.println("Consumer01接收到消息"+message);
channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
}
};
boolean autoAck = false; channel.basicConsume(normalQueue, autoAck, deliverCallback, consumerTag -> { });
}
}
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3、C2消费者代码不变
