public static boolean isInteger(byte[] str, int off, int len) {
        if (str == null || len == 0) {
            return false;
        }

        char ch = (char) str[off];
        boolean sign = ch == '-' || ch == '+';
        if (sign) {
            if (len == 1) {
                return false;
            }
        } else if (ch < '0' || ch > '9') {
            return false;
        }

        final int end = off + len;
        for (int i = off + 1; i < end; ++i) {
            ch = (char) str[i];
            if (ch < '0' || ch > '9') {
                return false;
            }
        }
        return true;
    }
decimal is integer, check has non-zero small

@param decimal
@return
core/src/main/java/com/alibaba/fastjson2/util/TypeUtils.java