Buffered and Unbuffered Streams in Java

问题:

I was going through some of the documentation on Java IO and just wanted to make sure whether I get this right:

Unbuffered Input Streams: FileInputStream, InputStreamReader, FileReader

Unbuffered Output Streams: FileOutputStream, OutputStreamWriter, FileWriter

Buffered Output Streams: PrintStream, PrintWriter

In addition, we have the BufferedInputStream, BufferedOutputStream, BufferedReader and BufferedWriter streams to convert the unbuffered streams into buffered versions.

Finally, I observed that for the Character Streams, viz. InputStreamReader, FileReader, OutputStreamWriter, FileWriter, an internal byte-buffer is maintained for the bytes before they are sent into the stream. This byte-buffer is not under our control. Hence, for Character Streams, buffering refers to the high-level character buffer for storing the characters coming in and going out of the program.

Is everything I said correct?

P.S. - I understand that this buffering issue is somewhat implementation dependent, but I just wish to confirm what the javadocs are saying

回答1:

Rules of thumb:

1. Any InputStream / Reader that reads directly from an external source (FileInputStream, SocketInputStream, etc.) is 'raw' and considered unbuffered. (Though in reality, there is probably some buffering going on, depends on the implementation)

2. Any 'raw' InputStream or Reader can be buffered by a BufferedInputStream or BufferedReader.

3. Same assumptions for OuputStreams / Writers.

4. Other stream decorators (i.e. GZIPInputStream, MD5InputStream, YourSpecialObjectWriter) probably do some buffering, but its not very harmful to buffer the source.