if ("".equals(f)) { return s; } else if ("".equals(s)) { return f; }
    public static String append(String f, String s) {        f = f == null ? "" : f;        s = s == null ? "" : s;        if ("".equals(f)) {            return s;        } else if ("".equals(s)) {            return f;        }        StringBuffer result = new StringBuffer(f.length() + s.length());        for(int i = 0; i < f.length(); i++) {            char ch = f.charAt(i);            if (i + 1 == f.length() && ch == '/') {                break;            }            result.append(ch);        }        for(int i = 0; i < s.length(); i++) {            char ch = s.charAt(i);            if (i == 0 && ch != '/') {                result.append('/');            }            result.append(ch);        }        return result.toString();    }