问题
I'm using apache camel xml based paho routes for the subscription, publication process. While online, everything works fine. But I'm not able to receive the offline message.
I have set the following.,
- Constant Client ID
- Clean Session is FALSE,
- Both subscribed & published with QoS 2
With the standalone Program, it's getting all the offline messages. With the camel route it's not happening.
回答1:
Finally, I was able to solve this one manually.
Camel PAHO Client is not populating the callback function before performing the broker connection. They are doing it only when the connection is made.
So, once the connection is success then the broker just sends all the offline messages. In this case, our client does not have callback handlers to handle these messages. So they are lost.
Other clients (IoThub Client) which uses the PAHO internally is doing it right by setting the callback and initiating the connection.
来源：https://stackoverflow.com/questions/56248757/camel-paho-routes-not-receiving-offline-messages-while-connecting-back