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package edu.harvard.iq.dvn.core.web.util;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 *
 * @author xyang
 */
public class MD5Checksum implements java.io.Serializable {
    
    public MD5Checksum() {
    }
    
    public synchronized String CalculateMD5 (String datafile) {
        MessageDigest md = null;
        try {
            md = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }

        FileInputStream fis = null;
        try {
            fis = new FileInputStream(datafile);
        } catch (FileNotFoundException ex) {
            throw new RuntimeException(ex);
        }
        byte[] dataBytes = new byte[1024];

        int nread; 
        try {
            while ((nread = fis.read(dataBytes)) != -1) {
                md.update(dataBytes, 0, nread);
            }
        } catch (IOException ex) {
            throw new RuntimeException(ex);
        }

        byte[] mdbytes = md.digest();
        StringBuilder sb = new StringBuilder("");
        for (int i = 0; i < mdbytes.length; i++) {
            sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
        }
        return sb.toString();
    }
}