Why Matcher doesn't find pattern

Question

I'm agreed that regex is simple, but I really don't understand why it can't find and extract data. Also, I have very little experience with Java, may be it's the cause.

Method 1

String access_token = Utils.extractPattern(url, "access_token=([a-z0-9]+)&");

Url is like https://oauth.vk.com/blank.html#access_token=abcedefasdasdasdsadasasasdads123123&expires_in=0&user_id=1111111111

Utils

public static String extractPattern(String string, String pattern) {
    Pattern searchPattern = Pattern.compile(pattern);
    Matcher matcher = searchPattern.matcher(string);
    Log.d("pattern found - ", matcher.matches() ? "yes" : "no");
    return matcher.group();
}

Why it fails with java.lang.IllegalStateException: No successful match so far?

You have to call [`find`](https://docs.oracle.com/javase/8/docs/api/java/util/regex/Matcher.html#find--) first — Jorn Vernee, Jul 14 '17 at 23:13
`matcher.matches()` will not match a substring like the OP wants. Use `matcher.find()` instead. https://stackoverflow.com/questions/4450045/difference-between-matches-and-find-in-java-regex — tima, Jul 14 '17 at 23:20

score 4 · Accepted Answer · answered Jul 14 '17 at 23:23

You need to use find() method of Matcher class to check whether the Pattern is found or not. Here's the documentation:

Attempts to find the next subsequence of the input sequence that matches the pattern.

This method starts at the beginning of this matcher's region, or, if a previous invocation of the method was successful and the matcher has not since been reset, at the first character not matched by the previous match.

If the match succeeds then more information can be obtained via the start, end, and group methods.

Below should work:

public static String extractPattern(String string, String pattern) {
    Pattern searchPattern = Pattern.compile(pattern);
    Matcher matcher = searchPattern.matcher(string);
    if(matcher.find()){
        System.out.println("Pattern found");
        return matcher.group();
    }
    throw new IllegalArgumentException("Match not found");
}

Thanks for help. Would like to test, but remote service seems to work unstable. _Btw, should read the docs, but there's a lot of them on Java!_ — wapmorgan, Jul 14 '17 at 23:59

Why Matcher doesn't find pattern

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