Publish/Subscribe

**发布(Publish)、订阅(Subscribe)：**允许将同一个消息发送给多个消费者

**注意：**exchange负责消息路由，而不是存储，路由失败则消息丢失

常见的**X(exchange–交换机)***类型：

• Fanout 广播
• Direct 路由
• Topoc 话题

发布订阅–FanoutExchange

案例三：利用SpringAMQP演示广播交换机的使用

1.在消费者（consumer包）中，创建一个FanoutConfig类，声明队列、交换机，并将两者绑定

@Configuration
public class FanoutConfig {
   //声明FanoutExchange交换机itcast.fanout
    @Bean
    public FanoutExchange fanoutExchange(){
        return new FanoutExchange("itcast.fanout");
    }
    //声明fanout.queue1队列
    @Bean
    public Queue fanoutQueue1(){
        return new Queue("fanout.queue1");
    }
    //绑定fanout.queue1队列和交换机
    @Bean
    public Binding bindingQueue1(Queue fanoutQueue1, FanoutExchange fanoutExchange){
        return BindingBuilder.bind(fanoutQueue1).to(fanoutExchange);
    }
    //声明fanout.queue2队列
    @Bean
    public Queue fanoutQueue2(){
        return new Queue("fanout.queue2");
    }
    //绑定fanout.queue2队列和交换机
    @Bean
    public Binding bindingQueue2(Queue fanoutQueue2, FanoutExchange fanoutExchange){
        return BindingBuilder.bind(fanoutQueue2).to(fanoutExchange);
    }
}

2.在消费者（consumer包）中，编写两个消费者SpringRabbitListener方法，分别监听fanout.queue1和fanout.queue2

@Component
public class SpringRabbitListener {

    @RabbitListener(queues = "fanout.queue1")
    public void listenFanoutQueue1(String msg) {
        System.out.println("消费者接收到fanout.queue1的消息：【" + msg + "】");
    }
    @RabbitListener(queues = "fanout.queue2")
    public void listenFanoutQueue2(String msg) {
        System.out.println("消费者接收到fanout.queue2的消息：【" + msg + "】");
    }

}

3.在publiSher中编写测试方法，向itcast.fanout发送消息

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringAmqpTest {
    @Autowired
    private RabbitTemplate rabbitTemplate;
    
    @Test
    public void testSendFanoutExchange() {
        // 交换机名称
        String exchangeName = "itcast.fanout";
        // 消息
        String message = "hello, every one!";
        // 发送消息
        rabbitTemplate.convertAndSend(exchangeName, "", message);
    }
}

4.运行，结果

发布订阅–DirectExchange

将接收到的消息根据规则路由到指定的Queue，因此称为路由模式(routes)

• 每一个Queue都与Exchange设置一个BindingKey（暗号）
• 发布者发送消息时，指定消息的RoutingKey
• Exchange将消息路由到BindingKey与消息RoutingKey一致的队列

案例四：利用SpringAMQP演示DirectExchange的使用

1.直接用注解

@RabbitListener声明Exchange、Queue、RoutingKey

@QueueBinding注解用于绑定队列和交换器，并指定路由键

@Component
public class SpringRabbitListener {
	@RabbitListener(bindings = @QueueBinding(
            value = @Queue(name = "direct.queue1"),
            exchange = @Exchange(name = "itcast.direct", type = ExchangeTypes.DIRECT),
            key = {"red", "blue"}
    ))
    public void listenDirectQueue1(String msg){
        System.out.println("消费者接收到direct.queue1的消息：【" + msg + "】");
    }

    @RabbitListener(bindings = @QueueBinding(
            value = @Queue(name = "direct.queue2"),
            exchange = @Exchange(name = "itcast.direct", type = ExchangeTypes.DIRECT),
            key = {"red", "yellow"}
    ))
    public void listenDirectQueue2(String msg){
        System.out.println("消费者接收到direct.queue2的消息：【" + msg + "】");
    }


}

2.测试

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringAmqpTest {
    @Autowired
    private RabbitTemplate rabbitTemplate;
    
   @Test
    public void testSendDirectExchange() {
        // 交换机名称
        String exchangeName = "itcast.direct";
        // 消息
        String message = "hello, red!";
        // 发送消息
        rabbitTemplate.convertAndSend(exchangeName, "red", message);
    }
}

3.结果

发布订阅–TopicExchange

TopicExchange与DirectExchange类似，区别在于routingKey必须是多个单词的列表，并且以**.**分割

Queue与Exchange指定BindingKey时可以使用通配符

• # : 代指0个或多个单词
• * : 代指一个单词

案例五：利用SpringAMQP演示TopicExchange的使用

1.直接用注解

@RabbitListener声明Exchange、Queue、RoutingKey

@QueueBinding注解用于绑定队列和交换器，并指定路由键

@Component
public class SpringRabbitListener {
	 @RabbitListener(bindings = @QueueBinding(
            value = @Queue(name = "topic.queue1"),
            exchange = @Exchange(name = "itcast.topic", type = ExchangeTypes.TOPIC),
            key = "china.#"
    ))
    public void listenTopicQueue1(String msg){
        System.out.println("消费者接收到topic.queue1的消息：【" + msg + "】");
    }

    @RabbitListener(bindings = @QueueBinding(
            value = @Queue(name = "topic.queue2"),
            exchange = @Exchange(name = "itcast.topic", type = ExchangeTypes.TOPIC),
            key = "#.news"
    ))
    public void listenTopicQueue2(String msg){
        System.out.println("消费者接收到topic.queue2的消息：【" + msg + "】");
    }
}

2.测试

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringAmqpTest {
    @Autowired
    private RabbitTemplate rabbitTemplate;
    
    @Test
    public void testSendTopicExchange() {
        // 交换机名称
        String exchangeName = "itcast.topic";
        // 消息
        String message = "合理小姐是凑巧先生独一无二的女主角";
        //String message = "今天天气不错，我的心情好极了!";
        // 发送消息
         rabbitTemplate.convertAndSend(exchangeName, "china.news", message);
        //rabbitTemplate.convertAndSend(exchangeName, "china.weather", message);
    }

}

3.结果