search-scanner.java

import java.util.*;

private final static String SEARCH_TOKEN = "searchtoken";

public List<String> searchScanner() {
    Path file = Path.of(pathFile);
    List<String> found = new ArrayList<>();

    final Scanner scanner = new Scanner(file);
    while (scanner.hasNextLine()) {
        final String lineFromFile = scanner.nextLine();
        if (lineFromFile.contains(SEARCH_TOKEN)) {
            // a match!
            found.add(lineFromFile);
        }
    }
    return found;
}

related to medium article https://gae-piaz.medium.com/search-string-in-file-with-java-as-fast-as-possible-fedafdc7a3ee