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

FWIW, if you're opening a file in Java 8, you can use the Files.newBufferedReader(Path). I don't know how the performance compares to the other solutions described here, but at least it pushes the decision of what construct to buffer into the JDK.

Answer 2

r1 is more efficient. The InputStreamReader itself doesn't have a large buffer. The BufferedReader can be set to have a larger buffer than InputStreamReader. The InputStreamReader in r2 would act as a bottleneck.

In a nut: you should read the data through a funnel, not through a bottle.

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Update: here's a little benchmark program, just copy'n'paste'n'run it. You don't need to prepare files.

package com.stackoverflow.q3459127;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;

public class Test {

    public static void main(String... args) throws Exception {

        // Init.
        int bufferSize = 10240; // 10KB.
        int fileSize = 100 * 1024 * 1024; // 100MB.
        File file = new File("/temp.txt");

        // Create file (it's also a good JVM warmup).
        System.out.print("Creating file .. ");
        BufferedWriter writer = null;
        try {
            writer = new BufferedWriter(new FileWriter(file));
            for (int i = 0; i < fileSize; i++) {
                writer.write("0");
            }
            System.out.printf("finished, file size: %d MB.%n", file.length() / 1024 / 1024);
        } finally {
            if (writer != null) try { writer.close(); } catch (IOException ignore) {}
        }

        // Read through funnel.
        System.out.print("Reading through funnel .. ");
        Reader r1 = null;        
        try {
            r1 = new BufferedReader(new InputStreamReader(new FileInputStream(file), "UTF-8"), bufferSize);
            long st = System.nanoTime();
            for (int data; (data = r1.read()) > -1;);
            long et = System.nanoTime();
            System.out.printf("finished in %d ms.%n", (et - st) / 1000000);
        } finally {
            if (r1 != null) try { r1.close(); } catch (IOException ignore) {}
        }

        // Read through bottle.
        System.out.print("Reading through bottle .. ");
        Reader r2 = null;        
        try {
            r2 = new InputStreamReader(new BufferedInputStream(new FileInputStream(file), bufferSize), "UTF-8");
            long st = System.nanoTime();
            for (int data; (data = r2.read()) > -1;);
            long et = System.nanoTime();
            System.out.printf("finished in %d ms.%n", (et - st) / 1000000);
        } finally {
            if (r2 != null) try { r2.close(); } catch (IOException ignore) {}
        }

        // Cleanup.
        if (!file.delete()) System.err.printf("Oops, failed to delete %s. Cleanup yourself.%n", file.getAbsolutePath());
    }

}

Results at my Latitude E5500 with a Seagate Momentus 7200.3 harddisk:

Creating file .. finished, file size: 99 MB.
Reading through funnel .. finished in 1593 ms.
Reading through bottle .. finished in 7760 ms.

Answer 3

r1 is also more convenient when you read line-based stream as BufferedReader supports readLine method. You don't have to read content into a char array buffer or chars one by one. However, you have to cast r1 to BufferedReader or use that type explicitly for the variable.

I often use this code snippet:

BufferedReader br = ...
String line;
while((line=br.readLine())!=null) {
  //process line
}

Answer 4

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.