Buffer Size for BufferedInputStream

Question

How to determine the size of Buffer, while using Buffered Input Stream for reading batch of files? Is it based on the File size?I'm using,

byte[] buf = new byte[4096];

If i increase the buffer size,it will read quickly?

Answer 1

The default, which is deliberately undocumented, is 8192 bytes. Unless you have a compelling reason to change it, don't change it.

Answer 2

You can easily test it yourself, but it's not really a big issue. A few kilobytes is enough for the buffer, so you'll get good reading speeds.

If you profile your application and do realize that File IO is a performance bottleneck, there are ways to make it quicker, such as memorymapping a file.

Answer 3

What you show there is the "byte size" that you are reading into (the array).

If you are reading from a FileInputStream (i.e. non buffered), then changing that size will change the read size, yes.

This is different than the internal buffer used by BufferedInputStream. It doesn't have a getter but you can specify the size in the constructor and "remember it" from that I suppose. Default is 8K which may not be optimal.