Re: Lightning fast file reader?

• Subject: Re: Lightning fast file reader?
• From: Tim Boudreau <email@hidden>
• Date: Mon, 05 Apr 2004 11:47:49 +0200

I am trying to find a lightning fast way to read an ASCII text file (30-100 K bytes) for display in a scrolling file previewer. So far, I cannot do much better than the old readFile method (at the bottom of the listing below). Can anyone do better?

TIA,
Craig

/**
* Program: FastStreamCopy.java
* Author : Craig Mattocks
* Date : April, 2004
* Description: Use Java 1.4 NIO channels and buffers
* to read a file fast.
*/

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.text.NumberFormat;

public class FastStreamCopy
{
public static void main(String args[])
{
if (args.length != 1)
{
System.out.println("Usage: java FastStreamCopy filename");
System.exit(1);
}

NumberFormat digits = NumberFormat.getInstance();
digits.setMaximumFractionDigits(3);

long before;
long after;
double slowTime;
double fastTime;
double speedUp;

String filename = args[0];
String contents;

// Slow method
System.out.println("Reading file " + args[0] + " using slow method");
before = System.currentTimeMillis(); // Start timing
// contents = slowStreamCopy(filename);
contents = readFile(filename);
after = System.currentTimeMillis(); // End timing
slowTime = after - before;
// System.out.println("File's contents:\n" + contents);

// Fast method
System.out.println("Reading file " + args[0] + " using fast method");
before = System.currentTimeMillis(); // Start timing
contents = fastStreamCopy(filename);
after = System.currentTimeMillis(); // End timing
fastTime = after - before;
// System.out.println("File's contents:\n" + contents);

// Comparison
speedUp = 100d * slowTime/fastTime;
System.out.println("Slow method required " + slowTime + " ms.");
System.out.println("Fast method required " + fastTime + " ms.");
System.out.print("Speed up = " + digits.format(speedUp) + "% ");
System.out.println(speedUp > 100? "Good!":"Bad!");
}

/**
Read the contents of a text file using a memory-mapped byte buffer.

A MappedByteBuffer, is simply a special ByteBuffer. MappedByteBuffer
maps a region of a file directly in memory. Typically, that region
comprises the entire file, although it could map a portion. You must,
therefore, specify what part of the file to map. Moreover, as with
the other Buffer objects, no constructor exists; you must ask the
java.nio.channels.FileChannel for its map() method to get a
MappedByteBuffer.

Direct buffers allocate their data directly in the
runtime environment memory, bypassing the JVM|OS boundary,
usually doubling file copy speed. However, they generally
cost more to allocate.
*/
private static String fastStreamCopy(String filename)
{
String s = "";
FileChannel fc = null;
try
{
fc = new FileInputStream(filename).getChannel();

// int length = (int)fc.size();

MappedByteBuffer byteBuffer = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
// CharBuffer charBuffer = Charset.forName("ISO-8859-1").newDecoder().decode(byteBuffer);

// ByteBuffer byteBuffer = ByteBuffer.allocate(length);
// ByteBuffer byteBuffer = ByteBuffer.allocateDirect(length);
// CharBuffer charBuffer = byteBuffer.asCharBuffer();

// CharBuffer charBuffer = ByteBuffer.allocateDirect(length).asCharBuffer();
/*
int size = charBuffer.length();
if (size > 0)
{
StringBuffer sb = new StringBuffer(size);
for (int count=0; count<size; count++)
sb.append(charBuffer.get());
s = sb.toString();
}

if (length > 0)
{
StringBuffer sb = new StringBuffer(length);
for (int count=0; count<length; count++)
{
sb.append(byteBuffer.get());
}
s = sb.toString();
}
*/
int size = byteBuffer.capacity();
if (size > 0)
{
// Retrieve all bytes in the buffer
byteBuffer.clear();
byte[] bytes = new byte[size];
byteBuffer.get(bytes, 0, bytes.length);
s = new String(bytes);
}

fc.close();
}
catch (FileNotFoundException fnfx)
{
System.err.println("File not found: " + fnfx);
}
catch (IOException iox)
{
System.err.println("I/O problems: " + iox);
}
finally
{
if (fc != null)
{
try
{
fc.close();
}
catch (IOException ignore)
{
// ignore
}
}
}
return s;
}

private static String slowStreamCopy(String filename)
{
String s = "";

FileReader in = null;
try
{
File file = new File(filename);

int size = (int)file.length();

char[] buffer = new char[size];
in = new FileReader(file);

// int count = in.read(buffer, 0, size);
// if (count != -1)

int count;
while ((count = in.read(buffer, 0, size)) >= 0)
{
s = new String(buffer, 0, count);
}
in.close();
}
/*
String line;
BufferedReader in = null;
try
{
File file = new File(filename);
int size = (int)file.length();
if (size > 0)
{
StringBuffer sb = new StringBuffer(size);
in = new BufferedReader(new InputStreamReader(new FileInputStream(filename),"ISO-8859-1"));
while ((line = in.readLine()) != null)
{
sb.append(line);
}
in.close();
s = sb.toString();
}
}
*/
catch (FileNotFoundException fnfx)
{
System.err.println("File not found: " + fnfx);
}
catch (IOException iox)
{
System.err.println("I/O problems: " + iox);
}
finally
{
if (in != null)
{
try
{
in.close();
}
catch (IOException ignore)
{
// ignore
}
}
}
return s;
}

public static String readFile(String filename)
{
String s = "";
FileInputStream in = null;
// FileReader in = null;
try
{
File file = new File(filename);
byte[] buffer = new byte[(int) file.length()];
// char[] buffer = new char[(int) file.length()];
in = new FileInputStream(file);
// in = new FileReader(file);
in.read(buffer);
s = new String(buffer);
in.close();
}
catch (FileNotFoundException fnfx)
{
System.err.println("File not found: " + fnfx);
}
catch (IOException iox)
{
System.err.println("I/O problems: " + iox);
}
finally
{
if (in != null)
{
try
{
in.close();
}
catch (IOException ignore)
{
// ignore
}
}
}
return s;
}

}
------------------------------------------
"We scorch the earth, set fire to the sky.
We steep so low, to reach so high."
- "Red Hill Mining Town", Joshua Tree, U2
------------------------------------------
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