Question

I need to get a value from a file path.
assume my path looks like any other path:

c:\SomeFolder\SomeOtherfolder\A_Specific_Folder\what_i_want\another_folder\bla.txt

I can infer the name of ‘A_Specific_Folder’ at runtime, and i need to get ‘what_i_want’.
I know that ‘what_i_want’ is a number

I currenly use a regex like this:

public String getValueThatIneed(String path) {
    String regex = String.format("%s\\\\([0-9]+)\\\\", varContainingNameOfSpecificFolder); 
    Pattern p = Pattern.compile(regex);
    Matcher matcher = compile.matcher(path);
    matcher.find(); \\because otherwise i can't use matcher.start()
    String myValue = path.substring(matcher.start(1), matcher.end(1));
    return myValue;
}

All this just to get this tinyValue from one String.
Now assume that i must have this in a method because I use it in 10 places.
But in one of the places I suddenly need to do some other operation on the stirng that would again require me to do all the patter, matcher stuff, with the same regex, just to get matcher.end(1), because maybe thats all i need over there.

Is there shorter way to do this?

thanks.

Answer 1

I see several minor problems in your code:

• If varContainingNameOfSpecificFolder contains characters that have a meaning in regular expressions (. being the most likely candidate), then you must use Pattern.quote() to quote that part.
• your use of String.format() is unnecessary, you can use simply String concatenation using + here, which is easier to read.
• you don’t need the assignment to myValue, simply return the result of substring
• the substring call is unnecessary here! Simply replacing that expression with matcher.group(1) has the same effect!
• using String.replaceAll() might be a valid shortcut, but you’d have to modify your regex slightly.

So my version would be:

public static String getValueThatIneed(String path) {
    String regex = ".*\\\\" + Pattern.quote(varContainingNameOfSpecificFolder) + "\\\\([0-9]+)\\\\.*";
    String result = path.replaceAll(regex, "$1");
    if (result.equals(path)) {
        throw new IllegalArgumentException("<" + path + "> does not contain the thin i need!");
    }
    return result;
}

If you don’t care about error checking (as your code doesn’t do it either) you can simply return the result of the replaceAll() method and have a two-line method:

public static String getValueThatIneed(String path) {
    String regex = ".*\\\\" + Pattern.quote(varContainingNameOfSpecificFolder) + "\\\\([0-9]+)\\\\.*";
    return path.replaceAll(regex, "$1");
}

However, I strongly encourage you to keep it, as otherwise you can easily miss nasty bugs in your code.