Question

I have to compare files with java with a CRC32 code provided by a C# script. When I calculate the CRC32 with java.util.zip.CRC32 the result is completely different …

My guess is that the polynom = 0x2033 of the C# script is not the same as used in zip.CRC32. Is it possible to set the polynom ? Or any ideas of a java-class for calculating a CRC32 where you can define your own polynom?

UPDATE: problem is not the polymnom. This is the same between C# and Java

This is my code, maybe something is wrong in the way I read the file?

package com.mine.digits.internal.contentupdater;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.CRC32;

public class CRC 
{
    public static String doConvert32(File file)
    {
        byte[] bytes = readBytesFromFile(file); // readFromFile(file).getBytes();

        CRC32 x = new CRC32();
        x.update(bytes);

        return (Long.toHexString(x.getValue())).toUpperCase();
    }

    /** Read the contents of the given file. */
    private static byte[] readBytesFromFile(File file)
    {
        try
        {
            InputStream is = new FileInputStream(file);

            long length = file.length(); 
            if (length > Integer.MAX_VALUE) { 
                // File is too large 
            } 

            byte[] bytes = new byte[(int)length]; 
            int offset = 0; 
            int numRead = 0; 
            while (offset < bytes.length && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0)
            { 
                offset += numRead; 
            } 

            // Ensure all the bytes have been read in 
            if (offset < bytes.length) { 
                System.out.println("Could not completely read file " + file.getName()); 
            } 

            // Close the input stream and return bytes 
            is.close(); 

            return bytes;
        }
        catch (IOException e)
        {
            System.out.println("IOException " + file.getName()); 

            return null;
        }
    }
}

Thanks a lot,
Frank

Answer 1

Solved by copying the code from C# and convert it to a Java-class…

So now both use the same code, only had to do some minor changes for unsigned <> signed bytes differences.