Hi!

> From personal experience, I've found working with it
> to be awkward and brittle. I would much prefer to have each provider
> subclass FileSystemOptions and provide the getters and setters there. Then,
> at least, you could do an instanceof on the FileSystemOptions and determine
> what options are actually supposed to be there.

Look, The FileSystemOptions holds options for various filesystem 
implementations - at the same time!
The reason for this is, that, given the url is provided by the user, you simply 
do not know which real implementation will be used.
Thus, you have to provide e.g. ftp settings and sftp settings at the same time 
and let VFS decide which options to use - depending on the URL provided by the 
user.

Why would you like to pass in an option-set using a concrete config class if 
the URL is anything else then "concrete".
Also, a layered filesystem might require different settings e.g. 
compression-level of a zip-file on an ftp share.

This might require you to configure the zip filesystem (compression) AND the 
ftp filesystem (active/passive mode)

Also, the idea was to implement some sort of GlobalFileSystemOptions, the 
filesystem implementation then does not need to be changed, just the 
FileSystemOptions have to take care of that.


IF you use the options in a way which allows you to know which kind of 
filesystem will be used - good - but then the builder is just another layer, 
but not awkward and brittle I think.


I wont say that there aren't other ways to solve that, but using simple 
inheritance and instanceof is not the correct way.

Hmmm ... what I can think of is to refactor things that way:

* FileSystemOptions holds just a map of configurations like Map<Class, 
FileSystemOption>
* FileSystemOptions.set(Class vfsFilesystemClass, FileSystemOption options)

FileSystemOption then can be a concrete instance of a set of configurations for 
one specific filesystem, so you might have HttpFileSystemOption, 
SftpFileSystemOption etc. Each of them holding all possible filesystem options.

Sure, this completely breaks backward compatibility - and the 
GlobalFileSystemOptions thing needs to be solved somehow.

Ciao,
Mario

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