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A http toolkit for nebulas
There is a newer version: 0.0.6
package com.yanxisir.neb.utils;

import org.bouncycastle.jcajce.provider.digest.SHA3;

import java.util.Arrays;

/**
 * @author YanxiSir
 * @since 2018/5/3
 */
public class Base58 {

    public static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
    private static final char ENCODED_ZERO = ALPHABET[0];
    private static final int[] INDEXES = new int[128];

    static SHA3.DigestSHA3 digestSHA3 = new SHA3.Digest256();

    static {
        Arrays.fill(INDEXES, -1);
        for (int i = 0; i < ALPHABET.length; i++) {
            INDEXES[ALPHABET[i]] = i;
        }
    }

    public static String encode(byte[] input) {
        if (input.length == 0) {
            return "";
        }
        // Count leading zeros.
        int zeros = 0;
        while (zeros < input.length && input[zeros] == 0) {
            ++zeros;
        }
        // Convert base-256 digits to base-58 digits (plus conversion to ASCII characters)
        // since we modify it in-place
        input = Arrays.copyOf(input, input.length);
        // upper bound
        char[] encoded = new char[input.length * 2];
        int outputStart = encoded.length;
        for (int inputStart = zeros; inputStart < input.length; ) {
            encoded[--outputStart] = ALPHABET[divmod(input, inputStart, 256, 58)];
            if (input[inputStart] == 0) {
                ++inputStart; // optimization - skip leading zeros
            }
        }
        // Preserve exactly as many leading encoded zeros in output as there were leading zeros in input.
        while (outputStart < encoded.length && encoded[outputStart] == ENCODED_ZERO) {
            ++outputStart;
        }
        while (--zeros >= 0) {
            encoded[--outputStart] = ENCODED_ZERO;
        }
        // Return encoded string (including encoded leading zeros).
        return new String(encoded, outputStart, encoded.length - outputStart);
    }


    public static byte[] decode(String input) {
        if (input.length() == 0) {
            return new byte[0];
        }
        // Convert the base58-encoded ASCII chars to a base58 byte sequence (base58 digits).
        byte[] input58 = new byte[input.length()];
        for (int i = 0; i < input.length(); ++i) {
            char c = input.charAt(i);
            int digit = c < 128 ? INDEXES[c] : -1;
            if (digit < 0) {
                return new byte[0];
            }
            input58[i] = (byte) digit;
        }
        // Count leading zeros.
        int zeros = 0;
        while (zeros < input58.length && input58[zeros] == 0) {
            ++zeros;
        }
        // Convert base-58 digits to base-256 digits.
        byte[] decoded = new byte[input.length()];
        int outputStart = decoded.length;
        for (int inputStart = zeros; inputStart < input58.length; ) {
            decoded[--outputStart] = divmod(input58, inputStart, 58, 256);
            if (input58[inputStart] == 0) {
                ++inputStart; // optimization - skip leading zeros
            }
        }
        // Ignore extra leading zeroes that were added during the calculation.
        while (outputStart < decoded.length && decoded[outputStart] == 0) {
            ++outputStart;
        }
        // Return decoded data (including original number of leading zeros).
        return Arrays.copyOfRange(decoded, outputStart - zeros, decoded.length);
    }

    public static boolean decodeChecked(String input) {
        byte[] decoded = decode(input);
        if (decoded.length < 4) {
            return false;
        }
        byte[] data = Arrays.copyOfRange(decoded, 0, decoded.length - 4);
        byte[] checksum = Arrays.copyOfRange(decoded, decoded.length - 4, decoded.length);
        byte[] actualChecksum = Arrays.copyOfRange(digestSHA3.digest(data), 0, 4);
        if (!Arrays.equals(checksum, actualChecksum)) {
            return false;
        }
        return true;
    }

    private static byte divmod(byte[] number, int firstDigit, int base, int divisor) {
        // this is just long division which accounts for the base of the input digits
        int remainder = 0;
        for (int i = firstDigit; i < number.length; i++) {
            int digit = (int) number[i] & 0xFF;
            int temp = remainder * base + digit;
            number[i] = (byte) (temp / divisor);
            remainder = temp % divisor;
        }
        return (byte) remainder;
    }


    public static void main(String[] args) {
        String address = "n1SCj7jcgCHMVDBm6y9muo78uYg8L66svif";
        System.out.println("result:" + decodeChecked(address));
    }
}