Improve FolderObserver

[J-N-K]

Party fixes #3823

It has been reported that missing model directories cause issued during startup. With this PR a directory is created when it is missing.

[lolodomo]

Looks good

[J-N-K]

No, Not complete

[lolodomo]

Is it something we can include in 4.3 or is it still not yet ready?

[J-N-K]

Unfortunately I can't remember what is missing. IMO this is an improvement, even if it does not fully solve the issue. IIRC there are some corner-cases where it still does not work.

[holgerfriedrich]

@J-N-K I remember that I had seen the discussion in #3823 if this should be solved by creating the missing folders or learn more about the root cause. This is why I did not merge it at that time.

So shall we proceed merging this one to improve the situation?
If yes, maybe we should add a log message in case the directory is created, just as hint that something unexpected happened.
WDYT?

[kaikreuzer]

I have a general question here: The FolderObserver watches folders in the conf folder, right?
This folder is to be treated as read-only by openHAB (in contrast to the userdata folder), so creating directories in here does not look like the right approach to me.

[lolodomo]

Very good remark.
Maybe we should just log a warning to inform users that the folder is missing.
PS: it concerns only users using docker.

[J-N-K]

So the suggestion is

Path extensionPath = watchService.getWatchPath().resolve(extension);
if (!Files.isDirectory(extensionPath)) {
  logger.error("Model path for extension '{}' is missing or not accessible. Please create it and restart openHAB.", extension);
}

[wborn]

Maybe we should just log a warning to inform users that the folder is missing.
PS: it concerns only users using docker.

Yes some users just copy a few of their directories and think everything else will then magically work.
It's an issue for any distro so perhaps we should add something to the OH startup shell/batch files to detect this.

[Nadahar]

I don't fully understand what causes this problem, but as one user explains in #3823:

So, for openhab to launch correctly, the openhab/conf/items folder must be present. If it is not there, then the problems will be described above. My system does not have this folder, items are stored in the file openhab/userdata/jsondb/org.openhab.core.items.Item.json. After an empty folder has been created. All things changed the status from NOT_YET_READY to Online the next time openhab was launched.

If no Items files are in use, why must this folder exist? It doesn't seem logical to me, whether it's created or logged, it seems like the real problem is why the lack of this folder causes the system initialization to fail.