CRC32 checksum calculation Java NIO

Upasana | November 21, 2020 | 1 min read | 100 views

Few of the times we wish the speed of C and syntax of Java for doing some IO intensive task in Java. Calculation of CRC is one of them task which requires a efficient implementation in order to give good performance.

CRC32 calculation in Java

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.zip.CRC32;

class Scratch {

    public static long calculateCRC(File filename) {
        final int SIZE = 16 * 1024;
        try (FileInputStream in = new FileInputStream(filename);) {
            FileChannel channel = in.getChannel();
            CRC32 crc = new CRC32();
            int length = (int) channel.size();
            MappedByteBuffer mb = channel.map(FileChannel.MapMode.READ_ONLY, 0, length);
            byte[] bytes = new byte[SIZE];
            int nGet;
            while (mb.hasRemaining()) {
                nGet = Math.min(mb.remaining(), SIZE);
                mb.get(bytes, 0, nGet);
                crc.update(bytes, 0, nGet);
            }
            return crc.getValue();
        } catch (IOException e) {
            throw new RuntimeException("unknown IO error occurred ", e);
        }
    }
}

Java’s FileChannel’s provide much better performance than the BufferedInputStream and RandomAccessFile classes.