Communication between GUI and persistent backend (running in separate thread)

Hello I know there is many questions about it and some relevant answers. Like for returning response into GUI JTextArea from backend use SwingUtilities.invokeLater and for passing messages to backend using blocking queue. This I can work with.

But I would like to skip implementing queue's message parser. I would like to know if there is possible to directly call methods from another thread. Good partial answer is to call method using class implements runnable but it is only able to start a single task thread. What I'm looking for is a persistent object accepting more methods to be called from another thread and performing serialization.

So to say it more concretely:

1st thread is GUI having multiple button like "open device", "set reg A to user input", "set reg B to user input", "enable feature X", "flash FW"...

2nd is a working thread - it is already done consisting of multiple class. And having methods which needs to be called from GUI.

I need following properties

- working thread is only 1 and persistent through all GUI calls

- all GUI calls shall be serialized (another call is started only after first call is fully processed and returns)

- working thread shall be able to send some "log messages" into GUI (for example % of flashed FW) (this probably can be done easily by SwingUtilities.invokeLater)

Is there a better way to call methods than implement queue parser? If there is can you provide some link to good example? Or is the queue correct approach to this task? If the Queue is the correct approach how to best encode different parameters? Eg "flash firmware" button would need to pass "File", "set reg A to value XY" button would need to pass Byte...