多 Broker（或集群）支持

2.3 版本在单个应用与多个 broker 或 broker 集群通信时提供了更多便利。在消费者端，主要的好处是基础设施可以自动将自动声明的队列与相应的 broker 关联起来。

这最好通过一个例子来说明

@SpringBootApplication(exclude = RabbitAutoConfiguration.class)
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    CachingConnectionFactory cf1() {
        return new CachingConnectionFactory("localhost");
    }

    @Bean
    CachingConnectionFactory cf2() {
        return new CachingConnectionFactory("otherHost");
    }

    @Bean
    CachingConnectionFactory cf3() {
        return new CachingConnectionFactory("thirdHost");
    }

    @Bean
    SimpleRoutingConnectionFactory rcf(CachingConnectionFactory cf1,
            CachingConnectionFactory cf2, CachingConnectionFactory cf3) {

        SimpleRoutingConnectionFactory rcf = new SimpleRoutingConnectionFactory();
        rcf.setDefaultTargetConnectionFactory(cf1);
        rcf.setTargetConnectionFactories(Map.of("one", cf1, "two", cf2, "three", cf3));
        return rcf;
    }

    @Bean("factory1-admin")
    RabbitAdmin admin1(CachingConnectionFactory cf1) {
        return new RabbitAdmin(cf1);
    }

    @Bean("factory2-admin")
    RabbitAdmin admin2(CachingConnectionFactory cf2) {
        return new RabbitAdmin(cf2);
    }

    @Bean("factory3-admin")
    RabbitAdmin admin3(CachingConnectionFactory cf3) {
        return new RabbitAdmin(cf3);
    }

    @Bean
    public RabbitListenerEndpointRegistry rabbitListenerEndpointRegistry() {
        return new RabbitListenerEndpointRegistry();
    }

    @Bean
    public RabbitListenerAnnotationBeanPostProcessor postProcessor(RabbitListenerEndpointRegistry registry) {
        MultiRabbitListenerAnnotationBeanPostProcessor postProcessor
                = new MultiRabbitListenerAnnotationBeanPostProcessor();
        postProcessor.setEndpointRegistry(registry);
        postProcessor.setContainerFactoryBeanName("defaultContainerFactory");
        return postProcessor;
    }

    @Bean
    public SimpleRabbitListenerContainerFactory factory1(CachingConnectionFactory cf1) {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        factory.setConnectionFactory(cf1);
        return factory;
    }

    @Bean
    public SimpleRabbitListenerContainerFactory factory2(CachingConnectionFactory cf2) {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        factory.setConnectionFactory(cf2);
        return factory;
    }

    @Bean
    public SimpleRabbitListenerContainerFactory factory3(CachingConnectionFactory cf3) {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        factory.setConnectionFactory(cf3);
        return factory;
    }

    @Bean
    RabbitTemplate template(SimpleRoutingConnectionFactory rcf) {
        return new RabbitTemplate(rcf);
    }

    @Bean
    ConnectionFactoryContextWrapper wrapper(SimpleRoutingConnectionFactory rcf) {
        return new ConnectionFactoryContextWrapper(rcf);
    }

}

@Component
class Listeners {

    @RabbitListener(queuesToDeclare = @Queue("q1"), containerFactory = "factory1")
    public void listen1(String in) {

    }

    @RabbitListener(queuesToDeclare = @Queue("q2"), containerFactory = "factory2")
    public void listen2(String in) {

    }

    @RabbitListener(queuesToDeclare = @Queue("q3"), containerFactory = "factory3")
    public void listen3(String in) {

    }

}

正如您所见，我们声明了 3 组基础设施（连接工厂、admin、容器工厂）。如前所述，@RabbitListener 可以定义要使用哪个容器工厂；在这种情况下，它们还使用了 queuesToDeclare，这会在 broker 上声明队列（如果不存在）。通过按照 <容器工厂名称>-admin 的约定命名 RabbitAdmin bean，基础设施能够确定哪个 admin 应该声明队列。这也适用于 bindings = @QueueBinding(…)，其中交换机和绑定也将被声明。对于 queues 则不起作用，因为它期望队列已经存在。

在生产者端，提供了一个方便的 ConnectionFactoryContextWrapper 类，以便更简单地使用路由连接工厂。

如上所示，已添加了一个带有路由键 one、two 和 three 的 SimpleRoutingConnectionFactory bean。还有一个使用了该工厂的 RabbitTemplate。这里是使用该模板和 wrapper 将消息路由到其中一个 broker 集群的示例。

@Bean
public ApplicationRunner runner(RabbitTemplate template, ConnectionFactoryContextWrapper wrapper) {
    return args -> {
        wrapper.run("one", () -> template.convertAndSend("q1", "toCluster1"));
        wrapper.run("two", () -> template.convertAndSend("q2", "toCluster2"));
        wrapper.run("three", () -> template.convertAndSend("q3", "toCluster3"));
    };
}