Question

I am using FileWriter and I have noticed strange behavior.
I buffer my collection myself and every x rows I use

 IOUtils.writelines(myList,"\n", writer );

It doesnt write to the file. I continue to call it with more lines and only after it is very full it writes to the file.
Does it use a buffer? I cant find it in its documentation.

Answer 1

The second sentence of the FileWriter class overview says:

The constructors of this class assume that the default character encoding and the default byte-buffer size are acceptable. To specify these values yourself, construct an OutputStreamWriter on a FileOutputStream.

(My emphasis)

So clearly it’s buffered (unless the default byte-buffer size is zero and they’re being really odd with their phrasing).

I suspect it’s just using an OutputStreamWriter on a FileOutputStream. Looking at OutputStreamWriter:

Each invocation of a write() method causes the encoding converter to be invoked on the given character(s). The resulting bytes are accumulated in a buffer before being written to the underlying output stream.

(My emphasis)

If you want to ensure that various buffers at various levels are flushed, to the extent you can, look at using the flush method.