spring boot实战(第十四篇)整合RabbitMQ源码分析前言

前言

本篇开始讲述Spring Boot如何整合RabbitMQ(实际上Spring就整合了RabbitMQ)。

RabbitAdmin

在上篇中遗留AmqpAdmin没有讲解，现在来看下该部分代码

public AmqpAdmin amqpAdmin(CachingConnectionFactory connectionFactory) {
		return new RabbitAdmin(connectionFactory);
	}

创建RabbitAdmin实例，调用构造方法

	public RabbitAdmin(ConnectionFactory connectionFactory) {
		this.connectionFactory = connectionFactory;
		Assert.notNull(connectionFactory, "ConnectionFactory must not be null");
		this.rabbitTemplate = new RabbitTemplate(connectionFactory);
	}

创建连接工厂、rabbitTemplate，其中ConnectionFactory采用上一篇中自定义bean

   public ConnectionFactory connectionFactory() {
        CachingConnectionFactory connectionFactory = new CachingConnectionFactory();
        connectionFactory.setAddresses("127.0.0.1:5672");
        connectionFactory.setUsername("guest");
        connectionFactory.setPassword("guest");
        connectionFactory.setPublisherConfirms(true); //必须要设置
        return connectionFactory;
    }

为CachingConnectionFactory实例，其缓存模式为通道缓存

	private volatile CacheMode cacheMode = CacheMode.CHANNEL;

接下来看下RabbitAdmin类定义：

public class RabbitAdmin implements AmqpAdmin, ApplicationContextAware, InitializingBean {
...
}

实现接口AmqpAdmin(定义若干RabbitMQ操作父接口),这里需要强调的是InitializingBean，实现该接口则会调用afterPropertiesSet方法

public void afterPropertiesSet() {

		synchronized (this.lifecycleMonitor) {

			if (this.running || !this.autoStartup) {
				return;
			}

			if (this.connectionFactory instanceof CachingConnectionFactory &&
					((CachingConnectionFactory) this.connectionFactory).getCacheMode() == CacheMode.CONNECTION) {
				logger.warn("RabbitAdmin auto declaration is not supported with CacheMode.CONNECTION");
				return;
			}

			this.connectionFactory.addConnectionListener(new ConnectionListener() {

				// Prevent stack overflow...
				private final AtomicBoolean initializing = new AtomicBoolean(false);

				@Override
				public void onCreate(Connection connection) {
					if (!initializing.compareAndSet(false, true)) {
						// If we are already initializing, we don't need to do it again...
						return;
					}
					try {
						 
						initialize();
					}
					finally {
						initializing.compareAndSet(true, false);
					}
				}

				@Override
				public void onClose(Connection connection) {
				}

			});

			this.running = true;

		}
	}

synchronized ( this . lifecycleMonitor )加锁保证同一时间只有一个线程访问该代码，随后调用 this . connectionFactory .addConnectionListener添加连接监听，各连接工厂关系:

实际调用为CachingConnectionFactory

public void addConnectionListener(ConnectionListener listener) {
		super.addConnectionListener(listener);
		// If the connection is already alive we assume that the new listener wants to be notified
		if (this.connection != null) {
			listener.onCreate(this.connection);
		}
	}

此时connection为null，无法执行到 listener .onCreate( this . connection ); 往 CompositeConnectionListener connectionListener中添加监听信息，最终保证在集合中

private List<ConnectionListener> delegates = new CopyOnWriteArrayList<ConnectionListener>();

这里添加的监听代码执行，在后面调用时再来讲解。

至此～～ RabbitAdmin创建完成。 

Exchange

接下来继续来看AmqpConfig.java中的代码

  @Bean
    public DirectExchange defaultExchange() {
        return new DirectExchange(EXCHANGE);
    }

以上代码创建一个交换机，交换机类型为direct

在申明交换机时需要指定交换机名称，默认创建可持久交换机

Queue

 public Queue queue() {
        return new Queue("spring-boot-queue", true); //队列持久
    }

默认创建可持久队列

Binding

 @Bean
    public Binding binding() {
        return BindingBuilder.bind(queue()).to(defaultExchange()).with(AmqpConfig.ROUTINGKEY);
    }

BindingBuilder.bind(queue()) 实现为：

public static DestinationConfigurer bind(Queue queue) {
		return new DestinationConfigurer(queue.getName(), DestinationType.QUEUE);
	}

DestinationConfigurer通过name、type区分不同配置信息，其to()方法为重载方法，传递参数为四种交换机，分别返回Xxx ExchangeRoutingKeyConfigurer,其中with方法返回Bingding实例，因此在Binding信息中存储了

队列、交换机、路由key等相关信息

public class Binding extends AbstractDeclarable {

	public static enum DestinationType {
		QUEUE, EXCHANGE;
	}

	private final String destination;

	private final String exchange;

	private final String routingKey;

	private final Map<String, Object> arguments;

	private final DestinationType destinationType;
...
}

以上信息理解都非常简单，下面来看比较复杂点的 SimpleMessageListenerContainer

SimpleMessageListenerContainer

@Bean
    public SimpleMessageListenerContainer messageContainer() {
        SimpleMessageListenerContainer container = new SimpleMessageListenerContainer(connectionFactory());
        container.setQueues(queue());
        container.setExposeListenerChannel(true);
        container.setMaxConcurrentConsumers(1);
        container.setConcurrentConsumers(1);
        container.setAcknowledgeMode(AcknowledgeMode.MANUAL); //设置确认模式手工确认
        container.setMessageListener(new ChannelAwareMessageListener() {

            @Override
            public void onMessage(Message message, Channel channel) throws Exception {
                byte[] body = message.getBody();
                System.out.println("receive msg : " + new String(body));
                channel.basicAck(message.getMessageProperties().getDeliveryTag(), false); //确认消息成功消费
            }
        });
        return container;
    }

查看其实现的接口，注意SmartLifecycle

接下来设置队列信息，在AbstractMessageListenerContainer

private volatile List<String> queueNames = new CopyOnWriteArrayList<String>();

添加队列信息

AbstractMessageListenerContainer# exposeListenerChannel设置为true

 container.setMaxConcurrentConsumers(1);
 container.setConcurrentConsumers(1);

设置并发消费者数量，默认情况为1

container.setAcknowledgeMode(AcknowledgeMode.MANUAL); //设置确认模式手工确认

设置消费者成功消费消息后确认模式，分为两种

• 自动模式，默认模式，在RabbitMQ Broker消息发送到消费者后自动删除
• 手动模式，消费者客户端显示编码确认消息消费完成，Broker给生产者发送回调，消息删除

接下来设置消费者端消息监听，为private volatile Object messageListener 赋值

到这里消息监听容器也创建完成了，但令人纳闷的时，消费者如何去消费消息呢？从这里完全看不出来。那么接下来看下SmartLifecycle接口

SmartLifecycle

熟悉Spring都应该知道该接口，其定义为：

public interface SmartLifecycle extends Lifecycle, Phased {

	boolean isAutoStartup();
	void stop(Runnable callback);

}

其中的isAutoStartup设置为true时，会自动调用Lifecycle接口中的start方法，既然我们为源码分析，也简单看下这个聪明的声明周期接口是如何实现它的聪明方法的

在 spring boot实战(第十篇)Spring boot Bean加载源码分析中讲到执行Bean加载时，调用AbstractApplicationContext#refresh()，其中存在一个方法调用finishRefresh()

	protected void finishRefresh() {
		// Initialize lifecycle processor for this context.
		initLifecycleProcessor();

		// Propagate refresh to lifecycle processor first.
		getLifecycleProcessor().onRefresh();

		// Publish the final event.
		publishEvent(new ContextRefreshedEvent(this));

		// Participate in LiveBeansView MBean, if active.
		LiveBeansView.registerApplicationContext(this);
	}

其中initLifecycleProcessor初始化生命周期处理器，

	protected void initLifecycleProcessor() {
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
			this.lifecycleProcessor =
					beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
			if (logger.isDebugEnabled()) {
				logger.debug("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
			}
		}
		else {
			DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
			defaultProcessor.setBeanFactory(beanFactory);
			this.lifecycleProcessor = defaultProcessor;
			beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
			if (logger.isDebugEnabled()) {
				logger.debug("Unable to locate LifecycleProcessor with name '" +
						LIFECYCLE_PROCESSOR_BEAN_NAME +
						"': using default [" + this.lifecycleProcessor + "]");
			}
		}
	}

注册DefaultLifecycleProcessor对应bean

getLifecycleProcessor().onRefresh()调用DefaultLifecycleProcessor中方法onRefresh，调用startBeans(true)

	private void startBeans(boolean autoStartupOnly) {
		Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
		Map<Integer, LifecycleGroup> phases = new HashMap<Integer, LifecycleGroup>();
		for (Map.Entry<String, ? extends Lifecycle> entry : lifecycleBeans.entrySet()) {
			Lifecycle bean = entry.getValue();
			if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
				int phase = getPhase(bean);
				LifecycleGroup group = phases.get(phase);
				if (group == null) {
					group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
					phases.put(phase, group);
				}
				group.add(entry.getKey(), bean);
			}
		}
		if (phases.size() > 0) {
			List<Integer> keys = new ArrayList<Integer>(phases.keySet());
			Collections.sort(keys);
			for (Integer key : keys) {
				phases.get(key).start();
			}
		}
	}

其中

Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();

获取所有实现Lifecycle接口bean，执行bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup()判断，如果bean同时也为Phased实例，则加入到LifecycleGroup中，随后phases.get(key).start()调用start方法

接下来要做的事情就很明显：要了解消费者具体如何实现，查看SimpleMessageListenerContainer中的start是如何实现的。

至此～～整合RabbitMQ源码分析准备工作完成，下一篇中正式解读消费者的实现。