For .net, try to convert Hex string to Byte array, function like:

(1) transfer to Hex string bytes
byte[] bytes = Convert.ToByte(hexString.Substring(iCounter * 2, 2), 16);

(2) get get base 64 string using:

Convert.ToBase64String(bytes );

For java implement:

just using:

Base64.encode(hexString.getBytes() )

But they have different the results, may I know what I miss in the Java code?