1.6 Channel常见方法

channel.exchangeDeclare()

• type：有direct、fanout、topic三种

• 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;

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

    /**
     * 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;

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;

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 deliveryTag, boolean multiple) throws IOException;

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;

channel.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 deliveryTag, boolean requeue) throws IOException;

channel.basicConsume(queueName, 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;

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;

channel.queueDeclare(queueName, 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
• autodelete：当没有任何消费者使用时，自动删除该队列

this means that the queue will be deleted when there are no more processes consuming messages from it.)

 /**
     * 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;

arguments中可以设置的常用属性