Calculating hash values for really big files

Question

I am using the following code to calculate the hash values of files
public static String hash(File f, String algorithm)
            throws IOException, NoSuchAlgorithmException {
        if (!f.isFile()) {
            throw new IOException("Not a file");
        RandomAccessFile raf = new RandomAccessFile(f, "r");
        byte b[] = new byte[(int) raf.length()];
        raf.readFully(b);
        raf.close();
        MessageDigest messageDigest = MessageDigest.getInstance(algorithm);
        messageDigest.update(b);
        return toHexString(messageDigest.digest());
    }Now the problem is, for really big files, 100 MB or over, I get an OutOfMemoryError.
I have used the -Xms and -Xms options to increase the JVM heap size, and untimately made it to work. However, I think this is lame and there is also a limit to the -Xmx option.
Is there any other way I can calculate the hash values of these really big files?
Thanks a lot in advance.

Answer 1

why do u open the file the way u do ?
why to u upload ALL the file AT ONCE into the memory ?
i would do it like this:
FileInputStream fis = new FileInputStream (f);
int fileSize = f.available();
byte buffer[] = new byte[1000];
MessageDigest messageDigest = MessageDigest.getInstance(algorithm);
for(int read = 0;read < fileSize;read +=1000;)
if(fis.available() > 1000)
fis.read(buffer, read, 1000);
else if(fis.available() > 0)
fis.read(buffer, read, fis.available());
else
break;
messageDigest.update(b);
fis.close();
return toHexString(messageDigest.digest());