With this example we are going to demonstrate how to calculate the CRC Sum of a file. The Cyclic Redundancy Check is a good way to detect errors and changes to data. In short, in order to calculate the CRC-32 Sum of a file we implemented four different methods :
- The
checksumInputStream(String filepath)method creates a FileInputStream by opening a connection to the file. - The
checksumBufferedInputStream(String filepath)method creates a BufferedInputStream to save the input stream. - The
checksumRandomAccessFile(String filepath)method creates a RandomAccessFile to read from the file. The mode argument is set for reading only. - The
checksumMappedFile(String filepath)method uses a MappedByteBuffer to map the file directly into memory in a Read-only mode, through its FileChannel. - In all methods a new CRC32 Object is created. The CRC32 Object is updated for every byte read from each file. The methods are invoked in a main() method and return the CRC32 value of the same file.
Note that for each method implementation time is also calculated, as shown in the output.
Let’s take a look at the code snippets and the result output that follow:
package com.javacodegeeks.snippets.core;
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;
public class Main {
public static long checksumInputStream(String filepath) throws IOException {
InputStream inputStreamn = new FileInputStream(filepath);
CRC32 crc = new CRC32();
int cnt;
while ((cnt = inputStreamn.read()) != -1) {
crc.update(cnt);
}
return crc.getValue();
}
public static long checksumBufferedInputStream(String filepath) throws IOException {
InputStream inputStream = new BufferedInputStream(new FileInputStream(filepath));
CRC32 crc = new CRC32();
int cnt;
while ((cnt = inputStream.read()) != -1) {
crc.update(cnt);
}
return crc.getValue();
}
public static long checksumRandomAccessFile(String filepath) throws IOException {
RandomAccessFile randAccfile = new RandomAccessFile(filepath, "r");
long length = randAccfile.length();
CRC32 crc = new CRC32();
for (long i = 0; i < length; i++) {
randAccfile.seek(i);
int cnt = randAccfile.readByte();
crc.update(cnt);
}
return crc.getValue();
}
public static long checksumMappedFile(String filepath) throws IOException {
FileInputStream inputStream = new FileInputStream(filepath);
FileChannel fileChannel = inputStream.getChannel();
int len = (int) fileChannel.size();
MappedByteBuffer buffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, len);
CRC32 crc = new CRC32();
for (int cnt = 0; cnt < len; cnt++) {
int i = buffer.get(cnt);
crc.update(i);
}
return crc.getValue();
}
public static void main(String[] args) throws IOException {
String filepath = "C:/Users/nikos7/Desktop/output.txt";
System.out.println("Input Strea method:");
long start_timer = System.currentTimeMillis();
long crc = checksumInputStream(filepath);
long end_timer = System.currentTimeMillis();
System.out.println(Long.toHexString(crc));
System.out.println((end_timer - start_timer) + " ms");
System.out.println("///////////////////////////////////////////////////////////");
System.out.println("Buffered Input Stream method:");
start_timer = System.currentTimeMillis();
crc = checksumBufferedInputStream(filepath);
end_timer = System.currentTimeMillis();
System.out.println(Long.toHexString(crc));
System.out.println((end_timer - start_timer) + " ms");
System.out.println("///////////////////////////////////////////////////////////");
System.out.println("Random Access File method:");
start_timer = System.currentTimeMillis();
crc = checksumRandomAccessFile(filepath);
end_timer = System.currentTimeMillis();
System.out.println(Long.toHexString(crc));
System.out.println((end_timer - start_timer) + " ms");
System.out.println("///////////////////////////////////////////////////////////");
System.out.println("Mapped File method:");
start_timer = System.currentTimeMillis();
crc = checksumMappedFile(filepath);
end_timer = System.currentTimeMillis();
System.out.println(Long.toHexString(crc));
System.out.println((end_timer - start_timer) + " ms");
}
}
Output:
Input Strea method:
94ccd63e
75 ms
///////////////////////////////////////////////////////////
Buffered Input Stream method:
94ccd63e
5 ms
///////////////////////////////////////////////////////////
Random Access File method:
94ccd63e
99 ms
///////////////////////////////////////////////////////////
Mapped File method:
94ccd63e
8 ms
This was an example of calculating the CRC Sum of a file in Java.
on big files like 1GB mapped is the fasted way
thank you for post
///////////////////////////////////////////////////////////
Buffered Input Stream method:
3ef92509
29903 ms
///////////////////////////////////////////////////////////
Mapped File method:
3ef92509
2949 ms