Contribute.java

import java.io.File;
import java.io.IOException;
import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Contribute {

    private static final String IP_DELIMETER = ".";
    private static final int HASH_LENGTH = 40;
    private static final String HASH_ALGO = "SHA-1";

    public static void main(String[] args) throws Exception {
        System.out.println(isBanned("example.minecraft.com"));
    }

    public static String hashServer(String serverAddress) {
        try {
            MessageDigest digest = MessageDigest.getInstance(HASH_ALGO);
            byte[] inputBytes = serverAddress.getBytes(StandardCharsets.UTF_8);
            byte[] hashedBytes = digest.digest(inputBytes);
            return String.format("%0" + (hashedBytes.length << 1) + "x", new BigInteger(1, hashedBytes));
        } catch (NoSuchAlgorithmException noSuchAlgorithmException) {
            //ignore - sha1 is available in all vm
            return "";
        }
    }

    public static boolean isBanned(String serverAddress) throws IOException {
        File bannedList = new File("./blockedservers.txt");
        List<String> lines = Files.readAllLines(bannedList.toPath());
        lines.parallelStream()
                .filter(line -> !line.startsWith(line))
                .filter(line -> !line.trim().isEmpty())
                .map(line -> line.substring(0, HASH_LENGTH))
                .anyMatch(hash -> {
                    if (hash.equals(hashServer(serverAddress.trim().toLowerCase()))) {
                        return true;
                    }

                    //\\ is used for escaping regEx
                    List<String> components = new ArrayList<>(Arrays.asList(serverAddress.split("\\" + IP_DELIMETER)));
                    boolean isIp = components.size() == 4;
                    if (isIp) {
                        for (String component : components) {
                            try {
                                int number = Integer.parseInt(component);
                                if (number < 0 || number > 255) {
                                    //ip range is from 0.0.0.0 to 255.255.255.255
                                    isIp = false;
                                    break;
                                }
                            } catch (NumberFormatException numberFormatException) {
                                //not a ip
                                isIp = false;
                                break;
                            }
                        }
                    }

                    while (components.size() > 1) {
                        components.remove(isIp ? (components.size() - 1) : 0);

                        String toTest;
                        if (isIp) {
                            //example: 0.0.0.*
                            toTest = String.join(IP_DELIMETER, components) + ".*";
                        } else {
                            //example: *.server.com
                            toTest = ("*." + String.join(IP_DELIMETER, components));
                        }

                        if (hash.equals(hashServer(toTest))) {
                            return true;
                        }
                    }

                    return false;
                });

        return false;
    }
}