Java recursion trying to split text into chunks evenly, padding at end

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Java

string

recursion

I am writing an encryption program for a course I am taking to learn Java. The method is supposed to split text into chunks, chunk size specified by user. ("3" = "XXX XXX XXX") I am then supposed to pad the end of the String with "x"s when the String doesn't split evenly. I have not written the part to pad the "x"s at the end yet, because my method is leaving the "oddballs" at the beginning. ("3" = "X XXX XXX XXX" or "XX XXX XXX" INSTEAD OF "XXX XXX XX" or "XXX XXX X") I have written my method below. Any advice would be greatly appreciated!

What I have tried:

public static String groupify(String str, int n){

        if(str.length() == 0)
            return str;
        char c = str.charAt(0);
        String s = " ";
        if(str.length() % n == 1)
            return c + s + groupify(str.substring(1), n);
        return c + groupify(str.substring(1), n);
    }