FileHash.java

/* Athena/Aegis Encrypted Chat Platform
 * FileHash.java: Creates secure hashes of data
 *
 * Copyright (C) 2010  OlympuSoft
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

import java.io.*;
import java.security.MessageDigest;

/**
 * Calculates the MD5 checksum of a file
 * @author OlympuSoft
 */
public class FileHash {

	/**
	 * Calculates the MD5 checksum of a file
	 * @param filename File to get the checksum of
	 * @return The checksum
	 * @throws Exception
	 */
	public static byte[] createChecksum(String filename) throws
			Exception {
		InputStream fis = new FileInputStream(filename);

		byte[] buffer = new byte[1024];
		MessageDigest complete = MessageDigest.getInstance("MD5");
		int numRead;
		do {
			numRead = fis.read(buffer);
			if (numRead > 0) {
				complete.update(buffer, 0, numRead);
			}
		} while (numRead != -1);
		fis.close();
		return complete.digest();
	}

	/**
	 * Convert the file to hex
	 * @param filename The file to work with
	 * @return The hex string
	 * @throws Exception
	 */
	public static String getMD5Checksum(String filename) throws Exception {
		byte[] b = createChecksum(filename);
		String result = "";
		for (int i = 0; i < b.length; i++) {
			result +=
					Integer.toString((b[i] & 0xff) + 0x100, 16).substring(1);
		}
		return result;
	}
}