1、Channel
1.1 channel.exchangeDeclare()：
type：有direct、fanout、topic三种：
fanout
fanout类型的Exchange路由规则非常简单，它会把所有发送到该Exchange的消息路由到所有与它绑定的Queue中
direct
direct类型的Exchange路由规则也很简单，它会把消息路由到那些binding key与routing key完全匹配的Queue中。
topic
规则就是模糊匹配，可以通过通配符满足一部分规则就可以传送。它的约定是：
routing key为一个句点号“. ”分隔的字符串（我们将被句点号“. ”分隔开的每一段独立的字符串称为一个单词），如“stock.usd.nyse”、“nyse.vmw”、“quick.orange.rabbit” binding key与routing key一样也是句点号“. ”分隔的字符串。
binding key中可以存在两种特殊字符“”与“#”，用于做模糊匹配，其中“”用于匹配一个单词，“#”用于匹配多个单词(可以是零个）
durable：true、false true：服务器重启会保留下来Exchange。警告：仅设置此选项，不代表消息持久化。即不保证重启后消息还在。
原文：true if we are declaring a durable exchange (the exchange will survive a server restart)
autoDelete:true、false.true:当已经没有消费者时，服务器是否可以删除该Exchange。
原文1：true if the server should delete the exchange when it is no longer in use。
/**
* Declare an exchange.
* @see com.rabbitmq.client.AMQP.Exchange.Declare
* @see com.rabbitmq.client.AMQP.Exchange.DeclareOk
* @param exchange the name of the exchange
* @param type the exchange type
* @param durable true if we are declaring a durable exchange (the exchange will survive a server restart)
* @param autoDelete true if the server should delete the exchange when it is no longer in use
* @param arguments other properties (construction arguments) for the exchange
* @return a declaration-confirm method to indicate the exchange was successfully declared
* @throws java.io.IOException if an error is encountered
*/
Exchange.DeclareOk exchangeDeclare(String exchange, String type, boolean durable, boolean autoDelete,
Map<String, Object> arguments) throws IOException;
1.2 chanel.basicQos()
prefetchSize：0
prefetchCount：会告诉RabbitMQ不要同时给一个消费者推送多于N个消息，即一旦有N个消息还没有ack，则该consumer将block掉，直到有消息ack
global：true\false 是否将上面设置应用于channel，简单点说，就是上面限制是channel级别的还是consumer级别
备注：据说prefetchSize 和global这两项，rabbitmq没有实现，暂且不研究
QoS = quality-of-service， 顾名思义，服务的质量。通常我们设计系统的时候不能完全排除故障或保证说没有故障，而应该设计有完善的异常处理机制。在出现错误的时候知道在哪里出现什么样子的错误，原因是什么，怎么去恢复或者处理才是真正应该去做的。在接收消息出现故障的时候我们可以通过RabbitMQ重发机制来处理。重发就有重发次数的限制，有些时候你不可能不限次数的重发，这取决于消息的大小，重要程度和处理方式。
甚至QoS是在接收端设置的。发送端没有任何变化，接收端的代码也比较简单，只需要加如下代码：
channel.BasicQos(0, 1, false);
代码第一个参数是可接收消息的大小的，但是似乎在客户端2.8.6版本中它必须为0，即使：不受限制。如果不输0，程序会在运行到这一行的时候报错，说还没有实现不为0的情况。第二个参数是处理消息最大的数量。举个例子，如果输入1，那如果接收一个消息，但是没有应答，则客户端不会收到下一个消息，消息只会在队列中阻塞。如果输入3，那么可以最多有3个消息不应答，如果到达了3个，则发送端发给这个接收方得消息只会在队列中，而接收方不会有接收到消息的事件产生。总结说，就是在下一次发送应答消息前，客户端可以收到的消息最大数量。第三个参数则设置了是不是针对整个Connection的，因为一个Connection可以有多个Channel，如果是false则说明只是针对于这个Channel的。
这种数量的设置，也为我们在多个客户端监控同一个queue的这种负载均衡环境下提供了更多的选择。
/**
* Request specific "quality of service" settings.
*
* These settings impose limits on the amount of data the server
* will deliver to consumers before requiring acknowledgements.
* Thus they provide a means of consumer-initiated flow control.
* @see com.rabbitmq.client.AMQP.Basic.Qos
* @param prefetchSize maximum amount of content (measured in
* octets) that the server will deliver, 0 if unlimited
* @param prefetchCount maximum number of messages that the server
* will deliver, 0 if unlimited
* @param global true if the settings should be applied to the
* entire channel rather than each consumer
* @throws java.io.IOException if an error is encountered
*/
void basicQos(int prefetchSize, int prefetchCount, boolean global) throws IOException;
1.3 channel.basicPublish()
routingKey：路由键，#匹配0个或多个单词，*匹配一个单词，在topic exchange做消息转发用
mandatory：true：如果exchange根据自身类型和消息routeKey无法找到一个符合条件的queue，那么会调用basic.return方法将消息返还给生产者。
false：出现上述情形broker会直接将消息扔掉
immediate：true：如果exchange在将消息route到queue(s)时发现对应的queue上没有消费者，那么这条消息不会放入队列中。
当与消息routeKey关联的所有queue(一个或多个)都没有消费者时，该消息会通过basic.return方法返还给生产者。
BasicProperties ：需要注意的是BasicProperties.deliveryMode，0:不持久化 1：持久化
这里指的是消息的持久化，配合channel(durable=true),queue(durable)可以实现，即使服务器宕机，消息仍然保留
简单来说：mandatory标志告诉服务器至少将该消息route到一个队列中，否则将消息返还给生产者；
immediate标志告诉服务器如果该消息关联的queue上有消费者，则马上将消息投递给它，
如果所有queue都没有消费者，直接把消息返还给生产者，不用将消息入队列等待消费者了。
/**
* Publish a message.
*
* Publishing to a non-existent exchange will result in a channel-level
* protocol exception, which closes the channel.
*
* Invocations of <code>Channel#basicPublish</code> will eventually block if a
* <a href="http://www.rabbitmq.com/alarms.html">resource-driven alarm</a> is in effect.
*
* @see com.rabbitmq.client.AMQP.Basic.Publish
* @see <a href="http://www.rabbitmq.com/alarms.html">Resource-driven alarms</a>.
* @param exchange the exchange to publish the message to
* @param routingKey the routing key
* @param mandatory true if the 'mandatory' flag is to be set
* @param immediate true if the 'immediate' flag is to be
* set. Note that the RabbitMQ server does not support this flag.
* @param props other properties for the message - routing headers etc
* @param body the message body
* @throws java.io.IOException if an error is encountered
*/
void basicPublish(String exchange, String routingKey, boolean mandatory, boolean immediate, BasicProperties props, byte[] body)
throws IOException;
1.4 channel.basicAck();
deliveryTag:该消息的index
multiple：是否批量.true:将一次性ack所有小于deliveryTag的消息。
/**
* Acknowledge one or several received
* messages. Supply the deliveryTag from the {@link com.rabbitmq.client.AMQP.Basic.GetOk}
* or {@link com.rabbitmq.client.AMQP.Basic.Deliver} method
* containing the received message being acknowledged.
* @see com.rabbitmq.client.AMQP.Basic.Ack
* @param deliveryTag the tag from the received {@link com.rabbitmq.client.AMQP.Basic.GetOk} or {@link com.rabbitmq.client.AMQP.Basic.Deliver}
* @param multiple true to acknowledge all messages up to and
* including the supplied delivery tag; false to acknowledge just
* the supplied delivery tag.
* @throws java.io.IOException if an error is encountered
*/
void basicAck(long
1.5 channel.basicNack(delivery.getEnvelope().getDeliveryTag(), false, true);
deliveryTag:该消息的index
multiple：是否批量.true:将一次性拒绝所有小于deliveryTag的消息。
requeue：被拒绝的是否重新入队列
/**
* Reject one or several received messages.
*
* Supply the <code>deliveryTag</code> from the {@link com.rabbitmq.client.AMQP.Basic.GetOk}
* or {@link com.rabbitmq.client.AMQP.Basic.GetOk} method containing the message to be rejected.
* @see com.rabbitmq.client.AMQP.Basic.Nack
* @param deliveryTag the tag from the received {@link com.rabbitmq.client.AMQP.Basic.GetOk} or {@link com.rabbitmq.client.AMQP.Basic.Deliver}
* @param multiple true to reject all messages up to and including
* the supplied delivery tag; false to reject just the supplied
* delivery tag.
* @param requeue true if the rejected message(s) should be requeued rather
* than discarded/dead-lettered
* @throws java.io.IOException if an error is encountered
*/
void basicNack(long deliveryTag, boolean multiple, boolean requeue)
throws IOException;
1.6channel.basicReject(delivery.getEnvelope().getDeliveryTag(), false);
deliveryTag:该消息的index
requeue：被拒绝的是否重新入队列
channel.basicNack 与 channel.basicReject 的区别在于basicNack可以拒绝多条消息，而basicReject一次只能拒绝一条消息
/**
* Reject a message. Supply the deliveryTag from the {@link com.rabbitmq.client.AMQP.Basic.GetOk}
* or {@link com.rabbitmq.client.AMQP.Basic.Deliver} method
* containing the received message being rejected.
* @see com.rabbitmq.client.AMQP.Basic.Reject
* @param deliveryTag the tag from the received {@link com.rabbitmq.client.AMQP.Basic.GetOk} or {@link com.rabbitmq.client.AMQP.Basic.Deliver}
* @param requeue true if the rejected message should be requeued rather than discarded/dead-lettered
* @throws java.io.IOException if an error is encountered
*/
void basicReject(long
1.7 channel.basicConsume(QUEUE_NAME, true, consumer);
autoAck：是否自动ack，如果不自动ack，需要使用channel.ack、channel.nack、channel.basicReject 进行消息应答
/**
* Start a non-nolocal, non-exclusive consumer, with
* a server-generated consumerTag.
* @param queue the name of the queue
* @param autoAck true if the server should consider messages
* acknowledged once delivered; false if the server should expect
* explicit acknowledgements
* @param callback an interface to the consumer object
* @return the consumerTag generated by the server
* @throws java.io.IOException if an error is encountered
* @see com.rabbitmq.client.AMQP.Basic.Consume
* @see com.rabbitmq.client.AMQP.Basic.ConsumeOk
* @see #basicConsume(String, boolean, String, boolean, boolean, Map, Consumer)
*/
String basicConsume(String queue, boolean autoAck, Consumer callback) throws IOException;
1.8 chanel.exchangeBind()
channel.queueBind(queueName, EXCHANGE_NAME, bindingKey);
用于通过绑定bindingKey将queue到Exchange，之后便可以进行消息接收
/**
* Bind an exchange to an exchange, with no extra arguments.
* @see com.rabbitmq.client.AMQP.Exchange.Bind
* @see com.rabbitmq.client.AMQP.Exchange.BindOk
* @param destination the name of the exchange to which messages flow across the binding
* @param source the name of the exchange from which messages flow across the binding
* @param routingKey the routine key to use for the binding
* @return a binding-confirm method if the binding was successfully created
* @throws java.io.IOException if an error is encountered
*/
Exchange.BindOk exchangeBind(String destination, String source, String routingKey) throws IOException;
1.8 channel.queueDeclare(QUEUE_NAME, false, false, false, null);
durable：true、false true：在服务器重启时，能够存活
exclusive ：是否为当前连接的专用队列，在连接断开后，会自动删除该队列，生产环境中应该很少用到吧。
autodelete：当没有任何消费者使用时，自动删除该队列。
/**
* Declare a queue
* @see com.rabbitmq.client.AMQP.Queue.Declare
* @see com.rabbitmq.client.AMQP.Queue.DeclareOk
* @param queue the name of the queue
* @param durable true if we are declaring a durable queue (the queue will survive a server restart)
* @param exclusive true if we are declaring an exclusive queue (restricted to this connection)
* @param autoDelete true if we are declaring an autodelete queue (server will delete it when no longer in use)
* @param arguments other properties (construction arguments) for the queue
* @return a declaration-confirm method to indicate the queue was successfully declared
* @throws java.io.IOException if an error is encountered
*/
Queue.DeclareOk queueDeclare(String queue, boolean durable, boolean exclusive, boolean autoDelete,
Map<String, Object> arguments) throws IOException;
ref:RabbitMQ Channel 参数详解 -
