侦听消息队列的Message Listener类

Spring AMQP 是基于 Spring 框架的AMQP消息解决方案，提供模板化的发送和接收消息的抽象层，提供基于消息驱动的 POJO的消息监听等，简化了我们对于RabbitMQ相关程序的开发。

Spring AMQP包含一些模块，如：spring-amqp, spring-rabbit and spring-erlang等，每个模块分别由独立的一些Jar包组成。

AbstractAdaptableMessageListener用于在spring容器接收到消息后用于处理消息的抽象基类，如果需要使用自己定义的pojoL类来实现处理消息时，必须要继承该类，并实现onMessage()方法，如下：

public class MessageReceive extends AbstractAdaptableMessageListener {

    private static final Logger LOGGER = LoggerFactory.getLogger(MessageReceive.class);

    @Override
    public void onMessage(Message message, Channel channel) throws Exception {
        LOGGER.info("receive message:{}", new String(message.getBody(), "UTF-8"));
    }
}

实现了MessageListener, ChannelAwareMessageListener接口

MessageListener

@FunctionalInterface
public interface MessageListener {

	void onMessage(Message message);

}

@FunctionalInterface注解表示该接口是一个功能类接口

ChannelAwareMessageListener

@FunctionalInterface
public interface ChannelAwareMessageListener {

	/**
	 * Callback for processing a received Rabbit message.
	 * 
Implementors are supposed to process the given Message,
	 * typically sending reply messages through the given Session.
	 * @param message the received AMQP message (never null)
	 * @param channel the underlying Rabbit Channel (never null)
	 * @throws Exception Any.
	 */
	void onMessage(Message message, Channel channel) throws Exception;

}

在AbstractAdaptableMessageListener中实现了MessageListener类的onMessage(Message message)方法，其实际实现的还是ChannelAwareMessageListener类中的onMessage方法，channel设置为null

	@Override
	public void onMessage(Message message) {
		try {
			onMessage(message, null);
		}
		catch (Exception e) {
			throw new ListenerExecutionFailedException("Listener threw exception", e, message);
		}
	}

自定义消息处理的POJO类继承AbstractAdaptableMessageListener类后，重写onMessage方法，当spring容器接收消息后，会自动交由onMessage进行处理。