search-so.java

import java.util.*;
import org.apache.commons.lang3.SystemUtils;

public List<String> searchSo() {

    List<String> found = new ArrayList<>();

    // apache lang is awesome.
    if (SystemUtils.IS_OS_WINDOWS) {

        ProcessBuilder builder = new ProcessBuilder(
                "cmd.exe", "/c", "findstr " + SEARCH_TOKEN + " c:\\temp\\big.txt");
        builder.redirectErrorStream(true);
        Process p = builder.start();
        BufferedReader r = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line;
        while (true) {
            line = r.readLine();
            if (line == null) {
                break;
            }
            found.add(line);
        }

    } else if (SystemUtils.IS_OS_LINUX) {

        // well. do the same thing but with grep LOL

    } else {
        logger.error("So not supported.");
    }
  
    return found;
}

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