Yes, I tried BaseCode.decode(), but it does not work. 
My base64 string is "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=". 
but the BaseCode requires that base length must be a power of two. Then I tried to removed the "=",  but the result of decode is empty.