Usage of BufferedInputStream
If you are using a relatively large arrays to read the data a chunk at a time, then BufferedInputStream
will just introduce a wasteful copy. (Remember, read
does not necessarily read all of the array - you might want DataInputStream.readFully
). Where BufferedInputStream
wins is when making lots of small reads.
If you are consistently doing small reads then a BufferedInputStream
will give you significantly better performance. Each read request on an unbuffered stream typically results in a system call to the operating system to read the requested number of bytes. The overhead of doing a system call is may be thousands of machine instructions per syscall. A buffered stream reduces this by doing one large read for (say) up to 8k bytes into an internal buffer, and then handing out bytes from that buffer. This can drastically reduce the number of system calls.
However, if you are consistently doing large reads (e.g. 8k or more) then a BufferedInputStream
slows things a bit. You typically don't reduce the number of syscalls, and the buffering introduces an extra data copying step.
In your use-case (where you read a 20 byte chunk first then lots of large chunks) I'd say that using a BufferedInputStream
is more likely to reduce performance than increase it. But ultimately, it depends on the actual read patterns.