Base64 Base256

I have attached powerful functionality that converts from any base to any base and caters for any size values. Unfortunately it first converts to base10 and then to the other base; it is not a direct conversion. For this project you need to write functionality that DIRECTLY converts between Base64 and Base256. Also have a look at the code I have attached and let me know if there is a way to optimize the code; the code will be running in a multi-threaded environment. Note: this is a java project