URI

[Saikiran Tedla]

Path path1 = Paths.get(new URI("file://pandas/cuddly.png")); // THROWS EXCEPTION  	// AT RUNTIME

Path path2 = Paths.get(new URI("file:///c:/zoo-info/November/employees.txt"));

Path path3 = Paths.get(new URI("file:///home/zoodirectory"));

I saw this code in OCPJP SE 8 preparation book written by Boyarsky and Selikoff. I don't understand why the first one throws an exception but the third one doesn't. I tried running it through my compiler but no RuntimeException was thrown. I am really confused. What am I missing?

[Jeanne Boyarsky]

Are you saying the first one doesn't throw an exception on your machine? It does on a Mac:

Exception in thread "main" java.lang.IllegalArgumentException: URI has an authority component
at sun.nio.fs.UnixUriUtils.fromUri(UnixUriUtils.java:53)
at sun.nio.fs.UnixFileSystemProvider.getPath(UnixFileSystemProvider.java:98)
at java.nio.file.Paths.get(Paths.java:138)


I'm guessing you are on Windows?

In any case, it is wrong because a URI needs to be an absolute reference so Java can find it.

[Tim Holloway]

Actually, URI "file://pandas/cuddly.org" should properly be referring to a relative file path. Subdirectory panda, filename, "cuddly.org".

For reasons left obscure, the syntax of a URL should conform to the following pattern:

<scheme>:[//<authority>][<path>][?<query>]

For example:

https://coderanch.com/context/etc

Jean's example seems to have parsed improperly and it's taking the "//" of the authority component as though it were the "//" which is the translated version of the "\\" of a CIFS UNC name.

If my memory is accurate, this would be the proper encoding for a UNC filepath:

file:////server/share/directory1/directory2/filename.ext

Two slashes for the authority marker, 2 to represent the UNC path \\server\share/directory1/directory2/filename.ext. Note that the URL

file://\\server\share\directory1\directory2\filename.ext is technically legal, but you can burn yourself using it, since in Java you have to double-up on backslashes when coding string literals to avoid getting zapped by the escape mechanism:

file://\\\\server\\share/directory1/directory2/filename.ext and other variations on this theme,

Likewise, for local relative file paths:

file://directory1/directory2/filename.ext

And absolute paths:

file:///basedirectory/directory1/filename.ext

For systems with a single root, such as Unix, Linux, and MacOS

And

file:///c:/basedirectory/directory1/filename.ext

for multi-rooted filesystems like Windows (there are variants on this syntax, but this is one of the cleanest).