Should I buffer the InputStream or the InputStreamReader?

Question

What are the differences (if any) between the following two buffering approaches?

Reader r1 = new BufferedReader(new InputStreamReader(in, \"UTF-8\"), bufferSize         


        

Answer 1

In response to Ross Studtman's question in the comment above (but also relevant to the OP):

BufferedReader reader = new BufferedReader(new InputStreamReader(new BufferedInputSream(inputStream), "UTF-8"));

The BufferedInputStream is superfluous (and likely harms performance due to extraneous copying). This is because the BufferedReader requests characters from the InputStreamReader in large chunks by calling InputStreamReader.read(char[], int, int), which in turn (through StreamDecoder) calls InputStream.read(byte[], int, int) to read a large block of bytes from the underlying InputStream.

You can convince yourself that this is so by running the following code:

new BufferedReader(new InputStreamReader(new ByteArrayInputStream("Hello world!".getBytes("UTF-8")) {

    @Override
    public synchronized int read() {
        System.err.println("ByteArrayInputStream.read()");
        return super.read();
    }

    @Override
    public synchronized int read(byte[] b, int off, int len) {
        System.err.println("ByteArrayInputStream.read(..., " + off + ", " + len + ')');
        return super.read(b, off, len);
    }

}, "UTF-8") {

    @Override
    public int read() throws IOException {
        System.err.println("InputStreamReader.read()");
        return super.read();
    }

    @Override
    public int read(char[] cbuf, int offset, int length) throws IOException {
        System.err.println("InputStreamReader.read(..., " + offset + ", " + length + ')');
        return super.read(cbuf, offset, length);
    }

}).read(); // read one character from the BufferedReader

You will see the following output:

InputStreamReader.read(..., 0, 8192)
ByteArrayInputStream.read(..., 0, 8192)

This demonstrates that the BufferedReader requests a large chunk of characters from the InputStreamReader, which in turn requests a large chunk of bytes from the underlying InputStream.