code: public boolean isUsable() {
          final Channel nettyChannel = unsafeNettyChannel();
          Boolean discardConn = nettyChannel.attr(ClientConnectionToChannelBridge.DISCARD_CONNECTION).get();
  
          if (!nettyChannel.isActive() || Boolean.TRUE == discardConn) {
              return false;
          }
  
          long nowMillis = System.currentTimeMillis();
          long idleTime = nowMillis - lastReturnToPoolTimeMillis;
          return idleTime < maxIdleTimeMillis;
      }
docs: Returns whether this connection is safe to be used at this moment. <br/>
  This makes sure that the underlying netty's channel is active as returned by
  {@link Channel#isActive()} and it has not passed the maximum idle time in the pool.
  
  @return {@code true} if the connection is usable.