交换机

1. direct
   路由键（RoutingKey）与交换机完全匹配交换机，完全匹配、单播的形式.
   一个key可以绑定多个队列
2. fanout
   扇出型交换机，Routingkey无效，消息发送给所有绑定了了交换机的队列
3. topic
   跟direct类似，但是支持模糊匹配（*代表一个部分，#代表0个或多个部分）
4. header
   与direct类似，性能差，很少用到

死信队列

• 原因
  1. nack或者reject的信息
  2. 超过ttl而过期的队列
  3. 队列满了放不下

demo代码（未封装的）

生产者：

public class TopicProducer {

  private static final String EXCHANGE_NAME = "topic-exchange";

  public static void main(String[] argv) throws Exception {
    ConnectionFactory factory = new ConnectionFactory();
    factory.setHost("localhost");
    try (Connection connection = factory.newConnection();
         Channel channel = connection.createChannel()) {

        channel.exchangeDeclare(EXCHANGE_NAME, "topic");

        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            String userInput = scanner.nextLine();
            String[] strings = userInput.split(" ");
            if (strings.length < 1) {
                continue;
            }
            String message = strings[0];
            String routingKey = strings[1];

            channel.basicPublish(EXCHANGE_NAME, routingKey, null, message.getBytes("UTF-8"));
            System.out.println(" [x] Sent '" + message + " with routing:" + routingKey + "'");
        }
    }
  }

消费者：

public class TopicConsumer {

  private static final String EXCHANGE_NAME = "topic-exchange";

  public static void main(String[] argv) throws Exception {
    ConnectionFactory factory = new ConnectionFactory();
    factory.setHost("localhost");
    Connection connection = factory.newConnection();
    Channel channel = connection.createChannel();

    channel.exchangeDeclare(EXCHANGE_NAME, "topic");

      // 创建队列
      String queueName = "frontend_queue";
      channel.queueDeclare(queueName, true, false, false, null);
      channel.queueBind(queueName, EXCHANGE_NAME, "#.前端.#");

      // 创建队列
      String queueName2 = "backend_queue";
      channel.queueDeclare(queueName2, true, false, false, null);
      channel.queueBind(queueName2, EXCHANGE_NAME, "#.后端.#");

      // 创建队列
      String queueName3 = "product_queue";
      channel.queueDeclare(queueName3, true, false, false, null);
      channel.queueBind(queueName3, EXCHANGE_NAME, "#.产品.#");

      System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

      DeliverCallback xiaoaDeliverCallback = (consumerTag, delivery) -> {
          String message = new String(delivery.getBody(), "UTF-8");
          System.out.println(" [xiaoa] Received '" +
                  delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");
      };

      DeliverCallback xiaobDeliverCallback = (consumerTag, delivery) -> {
          String message = new String(delivery.getBody(), "UTF-8");
          System.out.println(" [xiaob] Received '" +
                  delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");
      };

      DeliverCallback xiaocDeliverCallback = (consumerTag, delivery) -> {
          String message = new String(delivery.getBody(), "UTF-8");
          System.out.println(" [xiaoc] Received '" +
                  delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");
      };

      channel.basicConsume(queueName, true, xiaoaDeliverCallback, consumerTag -> {
      });
      channel.basicConsume(queueName2, true, xiaobDeliverCallback, consumerTag -> {
      });
      channel.basicConsume(queueName3, true, xiaocDeliverCallback, consumerTag -> {
      });
  }
}

优缺对比