java web app无法访问linux文件系统

Trying to access file system from java web app, situation is user uploads an image and then image is ftped to another place for storage.I'm stuck on how to access the file after the upload it, i'm using the tomahawk lib for the upload which leaves me with a byte[] object after the upload so i need to convert the bytes to an image file and then ftp..this is where i get stuck. I couldn get the part with (new File..) to work.Trying to access file system from java web app,