Whether the message broker is currently available and able to process messages.
<p>Note that this is in addition to the {@link #isRunning()} flag, which
indicates whether this message handler is running. In other words the message
handler must first be running and then the {@code #isBrokerAvailable()} flag
may still independently alternate between being on and off depending on the
concrete sub-class implementation.
<p>Application components may implement
{@code hunt.framework.context.ApplicationListener<BrokerAvailabilityEvent>}
to receive notifications when broker becomes available and unavailable.
Whether the message broker is currently available and able to process messages. <p>Note that this is in addition to the {@link #isRunning()} flag, which indicates whether this message handler is running. In other words the message handler must first be running and then the {@code #isBrokerAvailable()} flag may still independently alternate between being on and off depending on the concrete sub-class implementation. <p>Application components may implement {@code hunt.framework.context.ApplicationListener<BrokerAvailabilityEvent>} to receive notifications when broker becomes available and unavailable.