How to convert byte array to custom base string?

Question

I know there are ways to convert to Base36 with toString or Base64 with encodeToString . However, I would like to how to do it. For example, I am using

private static final String BASE = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_=!@#$%^&*()[]{}|;:,.<>/?`~ \\'\"+-";

I am able to do it with int with the following code.

private String convertBase(int num) {
    String text = "";
    int j = (int) Math.ceil(Math.log(num) / Math.log(BASE.length()));
    for (int i = 0; i < j; i++) {
        text += BASE.charAt(num % BASE.length());
        num /= BASE.length();
    }
    return text;
}

However, the numerical value of the byte[] is bigger than long .

Answer 1

Ok, I found the answer myself. I used BigInteger to solve it.

public String baseConvert(final BigInteger number, final String charset) {
    BigInteger quotient;
    BigInteger remainder;
    final StringBuilder result = new StringBuilder();
    final BigInteger base = BigInteger.valueOf(charset.length());
    do {
        remainder = number.remainder(base);
        quotient = number.divide(base);
        result.append(charset.charAt(remainder.intValue()));
        number = number.divide(base);
    } while (!BigInteger.ZERO.equals(quotient));
    return result.reverse().toString();
}