1、Channel
1.1 channel.exchangeDeclare()：
type：有direct、fanout、topic三種：
fanout
fanout類型的Exchange路由規則非常簡單，它會把所有發送到該Exchange的消息路由到所有與它綁定的Queue中
direct
direct類型的Exchange路由規則也很簡單，它會把消息路由到那些binding key與routing key完全匹配的Queue中。
topic
規則就是模糊匹配，可以通過通配符滿足一部分規則就可以傳送。它的約定是：
routing key為一個句點號“. ”分隔的字符串（我們將被句點號“. ”分隔開的每一段獨立的字符串稱為一個單詞），如“stock.usd.nyse”、“nyse.vmw”、“quick.orange.rabbit” binding key與routing key一樣也是句點號“. ”分隔的字符串。
binding key中可以存在兩種特殊字符“”與“#”，用於做模糊匹配，其中“”用於匹配一個單詞，“#”用於匹配多個單詞(可以是零個）
durable：true、false true：服務器重啟會保留下來Exchange。警告：僅設置此選項，不代表消息持久化。即不保證重啟后消息還在。
原文：true if we are declaring a durable exchange (the exchange will survive a server restart)
autoDelete:true、false.true:當已經沒有消費者時，服務器是否可以刪除該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：會告訴RabbitMQ不要同時給一個消費者推送多於N個消息，即一旦有N個消息還沒有ack，則該consumer將block掉，直到有消息ack
global：true\false 是否將上面設置應用於channel，簡單點說，就是上面限制是channel級別的還是consumer級別
備注：據說prefetchSize 和global這兩項，rabbitmq沒有實現，暫且不研究
QoS = quality-of-service， 顧名思義，服務的質量。通常我們設計系統的時候不能完全排除故障或保證說沒有故障，而應該設計有完善的異常處理機制。在出現錯誤的時候知道在哪里出現什么樣子的錯誤，原因是什么，怎么去恢復或者處理才是真正應該去做的。在接收消息出現故障的時候我們可以通過RabbitMQ重發機制來處理。重發就有重發次數的限制，有些時候你不可能不限次數的重發，這取決於消息的大小，重要程度和處理方式。
甚至QoS是在接收端設置的。發送端沒有任何變化，接收端的代碼也比較簡單，只需要加如下代碼：
channel.BasicQos(0, 1, false);
代碼第一個參數是可接收消息的大小的，但是似乎在客戶端2.8.6版本中它必須為0，即使：不受限制。如果不輸0，程序會在運行到這一行的時候報錯，說還沒有實現不為0的情況。第二個參數是處理消息最大的數量。舉個例子，如果輸入1，那如果接收一個消息，但是沒有應答，則客戶端不會收到下一個消息，消息只會在隊列中阻塞。如果輸入3，那么可以最多有3個消息不應答，如果到達了3個，則發送端發給這個接收方得消息只會在隊列中，而接收方不會有接收到消息的事件產生。總結說，就是在下一次發送應答消息前，客戶端可以收到的消息最大數量。第三個參數則設置了是不是針對整個Connection的，因為一個Connection可以有多個Channel，如果是false則說明只是針對於這個Channel的。
這種數量的設置，也為我們在多個客戶端監控同一個queue的這種負載均衡環境下提供了更多的選擇。
/** * 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：路由鍵，#匹配0個或多個單詞，*匹配一個單詞，在topic exchange做消息轉發用
mandatory：true：如果exchange根據自身類型和消息routeKey無法找到一個符合條件的queue，那么會調用basic.return方法將消息返還給生產者。
false：出現上述情形broker會直接將消息扔掉
immediate：true：如果exchange在將消息route到queue(s)時發現對應的queue上沒有消費者，那么這條消息不會放入隊列中。
當與消息routeKey關聯的所有queue(一個或多個)都沒有消費者時，該消息會通過basic.return方法返還給生產者。
BasicProperties ：需要注意的是BasicProperties.deliveryMode，0:不持久化 1：持久化
這里指的是消息的持久化，配合channel(durable=true),queue(durable)可以實現，即使服務器宕機，消息仍然保留
簡單來說：mandatory標志告訴服務器至少將該消息route到一個隊列中，否則將消息返還給生產者；
immediate標志告訴服務器如果該消息關聯的queue上有消費者，則馬上將消息投遞給它，
如果所有queue都沒有消費者，直接把消息返還給生產者，不用將消息入隊列等待消費者了。
/** * 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:該消息的index
multiple：是否批量.true:將一次性ack所有小於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 deliveryTag, boolean multiple) throws IOException;
1.5 channel.basicNack(delivery.getEnvelope().getDeliveryTag(), false, true);
deliveryTag:該消息的index
multiple：是否批量.true:將一次性拒絕所有小於deliveryTag的消息。
requeue：被拒絕的是否重新入隊列
/** * 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:該消息的index
requeue：被拒絕的是否重新入隊列
channel.basicNack 與 channel.basicReject 的區別在於basicNack可以拒絕多條消息，而basicReject一次只能拒絕一條消息
/** * 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 deliveryTag, boolean requeue) throws IOException;
1.7 channel.basicConsume(QUEUE_NAME, true, consumer);
autoAck：是否自動ack，如果不自動ack，需要使用channel.ack、channel.nack、channel.basicReject 進行消息應答
/** * 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);
用於通過綁定bindingKey將queue到Exchange，之后便可以進行消息接收
/** * 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：在服務器重啟時，能夠存活
exclusive ：是否為當前連接的專用隊列，在連接斷開后，會自動刪除該隊列，生產環境中應該很少用到吧。
autodelete：當沒有任何消費者使用時，自動刪除該隊列。
/** * 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 參數詳解 - 簡書 (jianshu.com)