I came across FileBackedOutputStream class from Google Guava library and was wondering if it's suitable to be used as a kind of a buffer: once every day, a process in my webapp generates tens of thousands of lines (each containing about 100characters) which are then uploaded to a file on an FTP server. I was thinking of using a FileBackedOutputStream object to first write all these strings to and then give access to them to my FTP client by using FileBackedOutputStream.getSupplier().getInput(), which returns an InputStream. Would this be a correct use case for FileBackedOutputStream?
Yes, I think that would be an acceptable use case for FileBackedOutputStream. However, I think FileBackedOutputStream is best when you're using it with data that may vary in size considerably... for small amounts of data that can fit in memory without a problem you want to just buffer them in memory but for large amounts of data that might give you an OutOfMemoryError if you try to read it all in to memory, you want to switch to buffering to a file. This is where FileBackedOutputStream really shines I think. I've used it for buffering uploaded files that I need to do several things with.