Java Regex Issue with Quantifiers

Question

I'm using the following code using Java 7 to validate the format of a file:

private boolean validateFile(String image) {    
    // Get width and height on image
    ...
    ...
    //Multiply by three, once for each R,G, and B value for the pixel
    int entriesRequired = width * height * 3;
    Pattern pattern = Pattern.compile("w=\\d+\\s+h=\\d+\\s+OK\\s+[\\d+\\s+]{" + entriesRequired + "}");
    Matcher matcher = pattern.matcher(image);

    return matcher.matches();
}

The file, which I've read into a String and is being held by the image variable, appears as so:

"w=1\nh=2\nOK\n1\n2\n3\n4\n5\n6\n"

I'm expecting validateFile(String image) to return True, but it's been returning false. Any regex experts out there who can help me out?

Thanks, Josh

Answer 1

Your regex is wrong.

"w=\\d+\\s+h=\\d+\\s+OK\\s+[\\d+\\s+]{" + entriesRequired + "}"

[\\\\d+\\\\s+]{n} Means "String of length n created using any of \\d , \\s , + ."

What you want is \\d+\\s+ repeated n times, so change the brackets to parenthesis:

"w=\\d+\\s+h=\\d+\\s+OK\\s+(\\d+\\s+){" + entriesRequired + "}"

It works for me

---

Side note: in that particular case you don't need Pattern and Matcher , you can just use

image.matches("w=\\d+\\s+h=\\d+\\s+OK\\s+(\\d+\\s+){" + entriesRequired + "}");

Since your regex validates the entire string