Barcode Conversion from Base64 in Java

Our vendor is supposedly going to send us the contents of a barcode in Base64.  We had before agreed upon Hexadecimal, but alas, things have changed.  These are 2-D barcodes to be precise, PDF417 and Data Matrix.  I am unfortunately unsure of exactly how Base64 works and how I coud go about determining the conversion of Base64 to Hexadecimal so that I can use our existing hexadecimal conversion code to parse the fields out of the barcode and store the human-readable fields in our database.

Has anyone used a Base 64 conversion utility or have links to sites where I can read about it and perhaps see some coding  examples?  I am not even sure if I can take the whole Base 64 string or perhaps a specific quadrant and convert it to Hex or Binary or whatever and then read from there, so i am at the beginning of my research somewhat. Please Help!