Base64 Encoding safe for filenames?

Is Base64 encoding safe to use for filenames on Windows and Linux systems? From my research I have found that replacing all / characters of the result with - or _ should resolve any issues.

Can anyone provide more details on this?

Currently in Java I am using the following peice of code:

MessageDigest md5Digest = MessageDigest.getInstance("MD5");
md5Digest.reset();
md5Digest.update(plainText.getBytes());

byte[] digest = md5Digest.digest();

BASE64Encoder encoder = new BASE64Encoder();
hash = encoder.encode(digest);
hash.replace('/','_');