Source Code : This program computes the CRC checksum of a file

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This program computes the CRC checksum of a file

   
/*
   This program is a part of the companion code for Core Java 8th ed.
   (http://horstmann.com/corejava)

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.zip.CRC32;

/**
 * This program computes the CRC checksum of a file. <br>
 * Usage: java NIOTest filename
 * @version 1.01 2004-05-11
 * @author Cay Horstmann
 */
public class NIOTest
{
   public static long checksumInputStream(String filename) throws IOException
   {
      InputStream in = new FileInputStream(filename);
      CRC32 crc = new CRC32();

      int c;
      while ((c = in.read()) != -1)
         crc.update(c);
      return crc.getValue();
   }

   public static long checksumBufferedInputStream(String filename) throws IOException
   {
      InputStream in = new BufferedInputStream(new FileInputStream(filename));
      CRC32 crc = new CRC32();

      int c;
      while ((c = in.read()) != -1)
         crc.update(c);
      return crc.getValue();
   }

   public static long checksumRandomAccessFile(String filename) throws IOException
   {
      RandomAccessFile file = new RandomAccessFile(filename, "r");
      long length = file.length();
      CRC32 crc = new CRC32();

      for (long p = 0; p < length; p++)
      {
         file.seek(p);
         int c = file.readByte();
         crc.update(c);
      }
      return crc.getValue();
   }

   public static long checksumMappedFile(String filename) throws IOException
   {
      FileInputStream in = new FileInputStream(filename);
      FileChannel channel = in.getChannel();

      CRC32 crc = new CRC32();
      int length = (int) channel.size();
      MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, length);

      for (int p = 0; p < length; p++)
      {
         int c = buffer.get(p);
         crc.update(c);
      }
      return crc.getValue();
   }

   public static void main(String[] args) throws IOException
   {
      System.out.println("Input Stream:");
      long start = System.currentTimeMillis();
      long crcValue = checksumInputStream(args[0]);
      long end = System.currentTimeMillis();
      System.out.println(Long.toHexString(crcValue));
      System.out.println((end - start) + " milliseconds");

      System.out.println("Buffered Input Stream:");
      start = System.currentTimeMillis();
      crcValue = checksumBufferedInputStream(args[0]);
      end = System.currentTimeMillis();
      System.out.println(Long.toHexString(crcValue));
      System.out.println((end - start) + " milliseconds");

      System.out.println("Random Access File:");
      start = System.currentTimeMillis();
      crcValue = checksumRandomAccessFile(args[0]);
      end = System.currentTimeMillis();
      System.out.println(Long.toHexString(crcValue));
      System.out.println((end - start) + " milliseconds");

      System.out.println("Mapped File:");
      start = System.currentTimeMillis();
      crcValue = checksumMappedFile(args[0]);
      end = System.currentTimeMillis();
      System.out.println(Long.toHexString(crcValue));
      System.out.println((end - start) + " milliseconds");
   }
}

   
    
    
  

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