Checksum.java

/**
 * Copyright 2008 The University of North Carolina at Chapel Hill
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package edu.unc.lib.dl.util;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import org.apache.commons.codec.binary.Hex;

/**
 * A class to compute checksums. Expected usage: Use the default algorithm of
 * MD5 or set a different algorithm (must be supported by
 * java.security.MessageDigest). Then one can repeatedly call the various
 * "getChecksumFrom..." methods to get checksums.
 * 
 */
public class Checksum {
	private String algorithm = "MD5";
	private MessageDigest messageDigest = null;

	/**
	 * Constructor for Checksum class
	 */
	public Checksum() {
		try {
			initializeMessageDigest();
		} catch (NoSuchAlgorithmException e) {
			throw new Error("The default algorithm should be available.");
		}
	}

	public static void main(String[] args) {
		for (int i = 0; i < args.length; i++) {
			File file = new File(args[i]);
			Checksum checker = new Checksum();
			System.out.print(args[i]);
			System.out.print(":");
			try {
				System.out.print(checker.getChecksum(file));
			} catch (IOException e) {
				System.out.print(e.getMessage());
			}

		}
	}

	/**
	 * Initialize the internal message digest object if it is null
	 */
	private void initializeMessageDigest() throws NoSuchAlgorithmException {
		messageDigest = MessageDigest.getInstance(algorithm);
	}

	/**
	 * Get the checksum for the passed in file
	 * 
	 * @param file
	 *            must not be null
	 * @return byte array containing checksum
	 * @throws IOException
	 * @throws FileNotFoundException
	 */
	public String getChecksum(File file) throws IOException,
			FileNotFoundException {
		InputStream inputStream = new FileInputStream(file);
		return getChecksum(inputStream);
	}

	/**
	 * Get the checksum for the passed in String
	 * 
	 * @param string
	 *            must not be null
	 * @return byte array containing checksum
	 */
	public String getChecksum(String string) {
		return getChecksum(string.getBytes());
	}

	/**
	 * Get the checksum for the passed in byte array
	 * 
	 * @param byteArray
	 *            must not be null
	 * @return byte array containing checksum
	 */
	public String getChecksum(byte[] byteArray) {
		messageDigest.reset();
		messageDigest.update(byteArray);
		Hex hex = new Hex();
		return new String(hex.encode(messageDigest.digest()));
	}

	/**
	 * Get the checksum for the passed in byte array
	 * 
	 * @param byteArray
	 *            must not be null
	 * @return byte array containing checksum
	 */
	public String getChecksum(InputStream in) throws IOException {
		messageDigest.reset();
		try (BufferedInputStream bis = new BufferedInputStream(in, 1024)) {
			byte[] buffer = new byte[1024];
			int numRead;
			do {
				numRead = bis.read(buffer);
				if (numRead > 0) {
					messageDigest.update(buffer, 0, numRead);
				}
			} while (numRead != -1);
		}
		Hex hex = new Hex();
		return new String(hex.encode(messageDigest.digest()));
	}

	/**
	 * Get the message digest algorithm. Defaults to MD5.
	 * 
	 * @return The message digest algorithm
	 */
	public String getAlgorithm() {
		return algorithm;
	}

	/**
	 * Set the message digest algorithm and reset the internal message digest
	 * object. Algorithm must be set to one of the valid algorithms supported by
	 * java.security.MessageDigest . Calling this method will reset the internal
	 * message digest object, which is not safe to do if on another thread this
	 * same Checksum object is computing a checksum.
	 * 
	 * @param algorithm
	 *            The message digest algorithm
	 */
	public void setAlgorithm(String algorithm) throws NoSuchAlgorithmException {
		this.algorithm = algorithm;
		initializeMessageDigest();
	}
}