sample code of MessageDigest

Sha1.java

import java.security.MessageDigest;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Sha1 {

    private static void sha1ByMap(String file) throws IOException, NoSuchAlgorithmException {
        FileInputStream fis = new FileInputStream(file);
        long size = fis.available();
        FileChannel fileChan = fis.getChannel();
        ByteBuffer bytes = fileChan.map(FileChannel.MapMode.READ_ONLY, 0L, size);

        MessageDigest md = MessageDigest.getInstance("SHA-1");
        md.update(bytes);
        
        byte[] digest = md.digest();

        for (byte b : digest) {
            System.out.print(String.format("%02x", b));
        }
        System.out.println("");
    }

    private static void sha1ByRead(String file) throws IOException, NoSuchAlgorithmException {
        FileInputStream fis = new FileInputStream(file);
        byte[] bytes = new byte[4096];

        MessageDigest md = MessageDigest.getInstance("SHA-1");

        int size = 0;
        while ((size = fis.read(bytes)) > 0) {
            md.update(bytes, 0, size);
        }
        
        byte[] digest = md.digest();

        for (byte b : digest) {
            System.out.print(String.format("%02x", b));
        }
        System.out.println("");
    }

    public static void main(String[] args) throws IOException, NoSuchAlgorithmException {
        String file = args[0];
        sha1ByMap(file);
        sha1ByRead(file);
    }
}