Add a means to convert a URI to a JimfsPath

[eyalroth]

There is no obvious way to convert a URI into a JimfsPath. Normally, one could use fs.provider().getPath(uri), but this is not implemented by JimfsFileSystemProvider; instead, it throws an exception stating:

This method should not be called directly; use Paths.get(URI) instead.

Which is funny, since on #12 @cgdecker (main contributor to the project?)

strongly recommends not using Paths.get

I would've used JimfsFileSystem.toPath(URI), but the entire class is set to the package-private access modifier (why the hell?).

[cgdecker]

Paths.get(URI) is fine and is the correct way to get a Path from a URI... what I was referring to in that issue was Paths.get(String, String...), which can only get you a Path from the default file system.

And JimfsFileSystem is package-private because users should be able to do everything they need through the normal java.nio.file APIs without using implementation details of Jimfs itself. It's a bit unfortunate that fs.provider().getPath(uri) doesn't work; it's a side-effect of something else that had to be done.

[eyalroth]

Paths.get(URI) is doing nothing but finding the file-system provider which matches the URI's scheme and resolving the URI using said provider's getPath(URI) method. In case the scheme is file, the method will use the default file system, much like its "sister" Paths.get(String); therefore, the same argument could be said for this method as well.

In other words, I'm a user of Jimfs and I would've liked to convert URIs with the file scheme into a JimfsPath, the same way I'm able to do with the default file system (which is what I take Jimfs to be an emulator for). fs.provider().getPath(URI) is exactly the way to do this, and therefore I expect Jimfs to implement it. I would like to know what is the problem with implementing it; perhaps I could help.

[cgdecker]

For better or for worse, the design of the whole FileSystem / FileSystemProvider API is such that each FileSystemProvider must use its own URI scheme. Jimfs URIs start with jimfs:. From that perspective, a file: URI means a file on the default file system, period. Also, I'll note that fs.provider().getPath(URI) is not intended as a way of getting a Path for one FileSystem from a URI that belongs to a different FileSystemProvider. FileSystemProvider is an SPI type and generally not intended to be used by user code; FileSystem.provider() mostly exists because it allows FileSystem implementations to get at the provider when a Path is passed to one of their methods.

So, if you have a file: URI and want to get a Jimfs Path? First I'd ask where the URI is coming from. If you could, rather than getting a file: URI in the first place, call toUri() on a Jimfs Path to get the URI that you later want to turn into a Jimfs Path.

Alternatively, you can probably do fs.getPath(uri.getPath()) and it'll just work like you want.

If it doesn't, it might be that constructing a new URI like new URI(anyJimfsPath.getScheme(), anyJimfsPath.getAuthority(), uri.getPath(), null, null) will work, though I think that should basically be equivalent to the previous suggestion.

[eyalroth]

I see your point; the NIO API couples the default provider to the "file" scheme and it's quite hard to undo.

Yeah, fs.getPath(uri.getPath()) is exactly what I used instead (I didn't care for the authority here).

[o2themar]

So I'm having an issue with creating a new URI from a path and I tried using new URI(anyJimfsPath.getScheme(), anyJimfsPath.getAuthority(), uri.getPath(), null, null) but that didn't work. What I'm trying to do is create a new filesystem for a zip file using a path that was already created using Jimfs.
What I'm doing is this:
Path zipPath = pathFromJimfs;
URI zipURI = zipPath.toUri();
zipURI = new URI(zipURI.getScheme(), zipURI.getAuthority(), zipURI.getPath(), null, null);
Map<String, Object> env = new HashMap<>();
env.put("create", Boolean.toString(Files.notExists(outputZipAbsolutePath)));
env.put("encoding", "UTF-8");
FileSystem zipFileSystem = FileSystems.newFileSystem(zipURI, env);

I'm getting the following exception:
java.lang.IllegalArgumentException: uri (jimfs://11bee858-af79-4dee-aca1-5420ee1c8a00/pathtozip) may not have a path, query or fragment

I debugged the code and yes it does have a path that is not null.

Why isn't this working? I thought as long as the path object is jimfs then I can create a new filesystem using that path object and everything should work as is.

[cgdecker]

@o2themar You're getting that exception because you're calling FileSystems.newFileSystem(URI, Map) with a URI with the scheme jimfs. That tells Jimfs to create a new Jimfs file system, not a zip file system, and the URI for a Jimfs file system isn't allowed to have a path, query or fragment (because they don't make sense in that context).

The scheme for a zip file system is jar:<underlying file system scheme>, so in the case of a file in a Jimfs file system, jar:jimfs. So your code would probably work if you just pass "jar:" + zipURI.getScheme() as the scheme for your new URI.

That said, you should be able to get a zip file system for a Jimfs path by just calling FileSystems.newFileSystem(Path, Map):

Path zipPath = pathFromJimfs;
Map<String, Object> env = new HashMap<>();
env.put("create", Boolean.toString(Files.notExists(outputZipAbsolutePath)));
env.put("encoding", "UTF-8");
FileSystem zipFileSystem = FileSystems.newFileSystem(zipPath, env);

[eyalroth]

@cgdecker I got to review this issue again with the recent activity, and I'm appalled at my previous behavior. I apologize for the demanding and combative tone. I really appreciate the work and effort you put into this!