Java Regular Expression byte by byte

Question

I am looking for a way to incrementally apply a regular expression pattern, i.e. I am looking for a matcher which I can update with characters as they come in and which tells me on each character whether it is still matching or not.

Here is an illustration in code (MagicMatcherIAmLookingFor is the thing I am looking for, characterSource is something which I can query for new character, say an InputStreamReader for that matter):

final Pattern pattern = Pattern.compile("[0-9]+");
final MagicMatcherIAmLookingFor incrementalMatcher = pattern.magic();
final StringBuilder stringBuilder = new StringBuilder();
char character;
while (characterSource.isNotEOF()) {
    character = characterSource.getNextCharacter();
    incrementalMatcher.add(character);
    if (incrementalMatcher.matches()) {
        stringBuilder.append(character);
    } else {
        return result(
             stringBuilder.toString(),
             remaining(character, characterSource)
        );
    }
}

I did not find a way to utilize the existing java.util.regex.Pattern like that, but maybe I just did not find it. Or is there an alternative library to the built in regular expressions which provides such a feature?

I did not have any luck searching the web for it - all the results are completely swamped with how to use java regular expressions in the first place.

I am targeting Java 8+

Answer 1

Is this the kind of object you are looking for ?

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class MagicMatcher {

    private Pattern pattern;
    private Matcher matcher;
    private String stringToCheck;

    public MagicMatcher(Pattern p , String s) {
        pattern = p;
        stringToCheck = s;
        updateMatcher();
    }

    public boolean matches() {
        return matcher.matches();
    }

    private void updateMatcher() {
        matcher = pattern.matcher(stringToCheck);
    }

    public void setStringToCheck(String s) {
        stringToCheck = s;
        updateMatcher();
    }

    public String getStringToCheck() {
        return stringToCheck;
    }

    public void addCharacterToCheck(char c) {
       stringToCheck += c;
       updateMatcher();
    }

    public void addStringToCheck(String s) {
        stringToCheck += s;
        updateMatcher();
    }

}