Extract a custom HTML attribute from a string

Question

I need to extract data-user_idnumbers from a string

input string example

 data-user_id="987654" lorem epsem  lorem epsem  lorem epsem  lorem
 data-user_id="123456-6" lorem epsem epsem  lorem epsem
 <img src="abcd.com"/> lorem epsem  data-user_id="123456"

expected output

987654,123456-6,123456

Code I have (don't work)

private static String getIdFromLine(String inputLine) {
    Pattern p = Pattern.compile("(data-user_id=\"[0-9a-z]*\")");
    Matcher m = p.matcher(inputLine);
    if (m.find()) {
        String src = m.group(2);
    }

    return null;
}

Maroun · Accepted Answer · 2015-01-20 14:13:01Z

4

You should have this regex:

data-user_id=\"([0-9a-z-]+)\"

group(1) will contain the desired output.

Your code suffers from more problems; you're not looping on the result, instead of if you should have while loop:

while (m.find()) {
    //build the result here
{

edited Jan 20, 2015 at 14:13

answered Jan 20, 2015 at 14:05

Maroun

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Comments

Stephan · Accepted Answer · 2015-01-20 14:14:46Z

In order to avoid compiltation of the pattern on each method call, I would write the method like this:

private static Pattern DATA_USER_ID_PATTERN = //
        Pattern.compile("data-user_id=\"([0-9a-z-]+)\"");

private static String getIdFromLine(String inputLine) {
    String src = null;
    Matcher m = DATA_USER_ID_PATTERN.matcher(inputLine);
    if (m.find()) {
        src = m.group(1);
    }

    return src;
}

If you're sure that no multiple threads will call your method, you can write it like this:

private static Matcher DATA_USER_ID_MATCHER = //
        Pattern.compile("data-user_id=\"([0-9a-z-]+)\"").matcher("");

private static String getIdFromLine(String inputLine) {
    String src = null;
    Matcher m = DATA_USER_ID_MATCHER;

    m.reset(inputLine);
    if (m.find()) {
        src = m.group(1);
    }

    return src;
}

Andy Brown · Accepted Answer · 2015-01-20 14:11:16Z

There are a few issues with your attempt:

your regex expression doesn't match the - character (or uppercase letters, in case you need those)
you aren't building up your string to return
you aren't looping using while to get all the matches in a single string

EDIT you've now edited your question to have a different input string. It is not clear if you will have multiple matches per line now.

try:

private static String getIdFromLine(String inputLine) {
    Pattern p = Pattern.compile("data-user_id=\"([0-9a-zA-Z-]*)\"");
    Matcher m = p.matcher(inputLine);
    StringBuilder sb = new StringBuilder("");
    while (m.find()) {
        String src = m.group(1);
        sb.append(src + ",");
    }
    int len = sb.length();
    if (len > 0)
        sb.delete(len - 1, len);

    return sb.toString();
}

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