Java regular expression is not matching valid results [duplicate]

Question

I'm trying to write a simple java regular expression to extract out the video id of a given youtube video from its url. E.g for:

http://www.youtube.com/watch?v=-mzvAAuCo1c

I want to extract out: -mzvAAuCo1c.

Here's what I'm trying:

Pattern pattern = Pattern.compile("v=([^&]+)");
String url = "http://www.youtube.com/watch?v=-mzvAAuCo1c";
Matcher matcher = pattern.match(url);
System.out.println(matcher.getGroupCount() ); //outputs 1
System.out.println(matcher.matches() ); //returns false;
System.out.println( matcher.group(0) ); //throws exception, same for 1

What am I doing wrong?

Did your code even compile?

Terry Li
– Terry Li

2013-10-06 23:21:11 +00:00
Commented Oct 6, 2013 at 23:21 — Terry Li
– Terry Li, Commented Oct 6, 2013 at 23:21

Reimeus · Accepted Answer · 2013-10-06 23:40:18Z

2

Invoke find to match the partial String. Dont call matches after calling find - this will result in an IllegalStateException. You want to capture group 1 rather than 0 as the latter returns the full String

Pattern pattern = Pattern.compile("v=([^&]+)");
String url = "http://www.youtube.com/watch?v=-mzvAAuCo1c&foo=3";
Matcher matcher = pattern.matcher(url);
if (matcher.find()) {
    System.out.println(matcher.groupCount()); 
    System.out.println(matcher.group(1)); 
}

edited Oct 6, 2013 at 23:40

answered Oct 6, 2013 at 23:24

Reimeus

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Comments

Terry Li · Accepted Answer · 2013-10-06 23:28:30Z

Matcher matcher = pattern.match(url);
System.out.println(matcher.getGroupCount() ); //outputs 1

First, the two lines above do not even compile. Change them to:

Matcher matcher = pattern.matcher(url);
System.out.println(matcher.groupCount() ); //outputs 1

Second, your regular expression:

Pattern pattern = Pattern.compile("v=([^&]+)");

only matches part of the input, which is why

matcher.matches()

returns false. Change the regular expression to:

Pattern pattern = Pattern.compile(".*v=([^&]+)");

Finally, since matcher.matches() does not return true, the statement

matcher.group(0)

will throw an exception.

Fixed code:

        Pattern pattern = Pattern.compile(".*v=([^&]+)");
        String url = "http://www.youtube.com/watch?v=-mzvAAuCo1c";
        Matcher matcher = pattern.matcher(url);
        System.out.println(matcher.groupCount()); //outputs 1
        System.out.println(matcher.matches()); //returns true;
        System.out.println(matcher.group(1)); //returns -mzvAAuCo1c

Community · Accepted Answer · 2017-05-23 12:29:32Z

0

Try this

(?<=videos\/|v=)([\w-]+)

In use

public static void main(String[] args) {

String link = "http://gdata.youtube.com/feeds/api/videos/xTmi7zzUa-M&whatever";
String pattern = "(?:videos\\/|v=)([\\w-]+)";

Pattern compiledPattern = Pattern.compile(pattern);
Matcher matcher = compiledPattern.matcher(link);

if(matcher.find()){
    System.out.println(matcher.group());
    }
}

Found Here.

edited May 23, 2017 at 12:29

CommunityBot

11 silver badge

answered Oct 6, 2013 at 23:19

danmc

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