二、RabbitMQ-客户端源码之AMQConnection

上一篇文章（[一]RabbitMQ-客户端源码之ConnectionFactory）中阐述了conn.start()方法完成之后客户端就已经和broker建立了正常的连接，而这个Connection的关键就在于这个start()方法之内，下面我们来慢慢分析。

首先来看看start()方法的源码，这个方法有点长，这里拆开来一一分析，首先是注释：

/**
 * Start up the connection, including the MainLoop thread.
 * Sends the protocol
 * version negotiation header, and runs through
 * Connection.Start/.StartOk, Connection.Tune/.TuneOk, and then
 * calls Connection.Open and waits for the OpenOk. Sets heart-beat
 * and frame max values after tuning has taken place.
 * @throws IOException if an error is encountered
 * either before, or during, protocol negotiation;
 * sub-classes {@link ProtocolVersionMismatchException} and
 * {@link PossibleAuthenticationFailureException} will be thrown in the
 * corresponding circumstances. {@link AuthenticationFailureException}
 * will be thrown if the broker closes the connection with ACCESS_REFUSED.
 * If an exception is thrown, connection resources allocated can all be
 * garbage collected when the connection object is no longer referenced.
 */