Question

I need to get a file name from file’s absolute path (I am aware of the file.getName() method, but I cannot use it here).
EDIT: I cannot use file.getName() because I don’t need the file name only; I need the part of the file’s path as well (but again, not the entire absoulte path). I need the part of file’s path AFTER certain path provided.

Let’s say the file is located in the folder:

C:\Users\someUser

On windows machine, if I make a pattern string as follows:

String patternStr = "C:\\Users\\someUser\\(.*+)";

I get an exception: java.util.regex.PatternSyntaxException: Illegal/unsupported escape sequence for backslash.

If I use Pattern.quote(File.pathSeparator):

String patternStr = "C:" + Pattern.quote(File.separator) + "Users" + Pattern.quote(File.separator) + "someUser" + Pattern.quote(File.separator) + "(.*+)";

the resulting pattern string is: C:\Q;\EUsers\Q;\EsomeUser\Q;\E(.*+) which of course has no match with the actual fileName “C:\Users\someUser\myFile.txt”.

What am I missing here? What is the proper way to parse file name?

Answer 1

If you indeed want to use a regular expressions, you should use

String patternStr = "C:\\\\Users\\\\someUser\\\\(.*+)";
                       ^^       ^^          ^^

instead.

Why? Your string literal

"C:\\Users\\someUser\\(.*+)"

is compiled to

C:\Users\someUser\(.*+)

Since \ is used for escaping in regular expressions too, you’ll have to escape them “twice”.

---

Regarding your edit:

You probably want to have a look at URI.relativize(). Example:

File base = new File("C:/Users/someUser");
File file = new File("C:/Users/someUser/someDir/someFile.txt");

String relativePath = base.toURI().relativize(file.toURI()).getPath();

System.out.println(relativePath); // prints "someDir/someFile.txt"

(Note that / works as file-separator on Windows machines too.)

---

Btw, I don’t know what you have as File.separator on your system, but if it’s set to \, then

"C:" + Pattern.quote(File.separator) + "Users" + Pattern.quote(File.separator) +
    "someUser" + Pattern.quote(File.separator) + "(.*+)";

should yield

C:\Q\\EUsers\Q\\EsomeUser\Q\\E(.*+)