Memory Issue with encoding a file to base64

So it encodes the file ok and sends it in the request but when I run the automated test through Jenkins I get an 'out of memory' error on the step that is doing the encoding. I researched online and saw a potential solution where you use an outputstream for base64 instead and read in the bytes of the file in parts if that makes sense. I just can't get my head around coding it. Any ideas?

Thanks