Extract Hex colors from css using java

Question

I am simply trying to get all the Hex colors values form a css file. The hex value could be #fff or #ffffff so here are the regular expressions i used for this

"^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$"
"#([a-f0-9]{3}){1,2}/i"
"^#[0-9a-zA-F]{3}"

but not working at all.

i am expecting the result as

#996633 #333 #ccc #969696 ....

But getting nothing, any idea where i am going wrong?

Here is the code:

final String HEX_PATTERN_STRING = "^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$";
Pattern pattern = Pattern.compile(HEX_PATTERN_STRING);
try {
        final URL CSS = new URL("https://maxcdn.bootstrapcdn.com/.../bootstrap.min.css");
        URLConnection data = CSS.openConnection();
        StringBuilder result = new StringBuilder();
        try (BufferedReader in = new BufferedReader(
                new InputStreamReader(
                        data.getInputStream())
        )) {
            in.lines().forEach(result::append);

            Matcher matcher = pattern.matcher(result);
            while (matcher.find()) {
                System.out.println(matcher.group(0));
            }
            System.out.println("Done");
        }

    } catch (IOException ex) {
    }

I don't see you actually associating HEX_PATTERN_STRING with your Marcher anywhere. — Graham Nicol
– Graham Nicol, Commented Aug 23, 2016 at 8:37
Try using final String HEX_PATTERN_STRING = "#(?:[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})"; and add Pattern pattern = Pattern.compile(HEX_PATTERN_STRING); before the line starting with Matcher matcher. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 23, 2016 at 8:39

Wiktor Stribiżew · Accepted Answer · 2016-08-23 09:09:08Z

2

Note your pattern contains ^ (start of string) and $ (end of string) anchors, requiring a whole string match.

You need to remove these anchors.

You cannot use regex delimiters like /.../ either, as in Java regex, you can pass the modifiers as (?i) inside the pattern, or with the help of Pattern.CASE_INSENSITIVE flag (usually, with Pattern.UNICODE_CASE).

Also, if you do not need the numbers only, you may turn the capturing group into a non-capturing (?:...).

Use

final String HEX_PATTERN_STRING = "#(?:[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})";

edited Aug 23, 2016 at 9:09

answered Aug 23, 2016 at 8:47

Wiktor Stribiżew

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7 Comments

Mak Over a year ago

my bad i just forgot to put this line pattern = Pattern.compile(HEX_PATTERN_STRING); in my code btw i am declaring paatern. i am updating the question

Wiktor Stribiżew Over a year ago

Do not forget to indicate your expected result and explain what "does not work" means.

Wiktor Stribiżew Over a year ago

I believe all you need is just to remove the anchors. I double checked: you may pass the StringBuilder to the matcher, as it is converted by Java into a string internally.

Mak Over a year ago

@wikitor pattern.matcher(result.toString()) is the same as pattern.matcher(result) i guess . but still i tried result.toString() and no success.

Mak Over a year ago

oh damm you are right ^ and $ require the whole string match i just removed them and it worked

|

neoexpert · Accepted Answer · 2019-01-08 20:43:34Z

0

I'm using this pattern:

Pattern PATTERN_HEXCOLOR = Pattern.compile(
    "#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})\\b");

It does accept color values like

#FFF
#FFFFFF

And ignores invalid color values like

#FFFF or #FFFFFFF

answered Jan 8, 2019 at 20:43

neoexpert

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5 Comments

Wiktor Stribiżew Over a year ago

This regex will fail here. The original question does not set any condition on the context where to find the codes, the word boundary may not be the best option to use here.

neoexpert Over a year ago

But your pattern finds also color values like #ffff. I just checked that in my HTML editor APP wich highlights all the hex color values with corresponding color

neoexpert Over a year ago

In your example there are two incorrect color codes. So my pattern seems to be correct.

Wiktor Stribiżew Over a year ago

#ffff is a string containing #fff color code and a letter f

neoexpert Over a year ago

Yeah, at least the Chrome Browser does not accept CSS color codes like that.

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