How to split a path platform independent?

Question

I'm using the following code to get an array with all sub directories from a given path.

String[] subDirs = path.split(File.separator); 

I need the array to check if certain folders are at the right place in this path. This looked like a good solution until findBugs complains that File.separator is used as a regular expression. It seems that passing the windows file separator to a function that is building a regex from it is a bad idea because the backslash being an escape character.

How can I split the path in a cross platform way without using File.separator? Or is code like this okay?

String[] subDirs = path.split("/"); 

Answer 1

Literalizing pattern strings

Whenever you need to literalize an arbitraryString to be used as a regex pattern, use Pattern.quote:

From the API:

public static String quote(String s)

Returns a literal pattern String for the specified String. This method produces a String that can be used to create a Pattern that would match the string s as if it were a literal pattern. Metacharacters or escape sequences in the input sequence will be given no special meaning.

Parameters: s - The string to be literalized
Returns: A literal string replacement

This means that you can do the following:

String[] subDirs = path.split(Pattern.quote(File.separator));

---

Literalizing replacement strings

If you need to literalize an arbitrary replacement String, use Matcher.quoteReplacement.

From the API:

public static String quoteReplacement(String s)

Returns a literal replacement String for the specified String. This method produces a String that will work as a literal replacement s in the appendReplacement method of the Matcher class. The String produced will match the sequence of characters in s treated as a literal sequence. Slashes ('\') and dollar signs ('$') will be given no special meaning.

Parameters: s - The string to be literalized
Returns: A literal string replacement

This quoted replacement String is also useful in String.replaceFirst and String.replaceAll:

Note that backslashes (\) and dollar signs ($) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string. Use Matcher.quoteReplacement to suppress the special meaning of these characters, if desired.

---

Examples

    System.out.println(
        "O.M.G.".replaceAll(".", "!")
    ); // prints "!!!!!!"

    System.out.println(
        "O.M.G.".replaceAll(Pattern.quote("."), "!")
    ); // prints "O!M!G!"

    System.out.println(
        "Microsoft software".replaceAll("so", "$0")
    ); // prints "Microsoft software"

    System.out.println(
        "Microsoft software".replaceAll("so", Matcher.quoteReplacement("$0"))
    ); // prints "Micro$0ft $0ftware"

Answer 2

Use path.getParentFile() repeatedly to get all components of a path.

Discouraged way would be to path.replaceAll("\\", "/").split("/").