com.nridge.core.base.std.DigitalHash.java Source code

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Here is the source code for com.nridge.core.base.std.DigitalHash.java

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/*
 * NorthRidge Software, LLC - Copyright (c) 2019.
 *
 * 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 3 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, see <http://www.gnu.org/licenses/>.
 */

package com.nridge.core.base.std;

import org.apache.commons.lang3.StringUtils;

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

/**
 * The DigitalHash class provides a simple collection of methods to generate
 * digital hash sequence values (based on the MD5 message digest algorithm)
 * for <i>String</i> objects and files.
 * <p>
 *     Probability of two hashes accidentally colliding is 1 in 340 undecillion
 *     282 decillion 366 nonillion 920 octillion 938 septillion 463 sextillion
 *     463 quintillion 374 quadrillion 607 trillion 431 billion 768 million 211
 *     thousand 456.
 * </p>
 * <p>
 *     To have a 50% chance of any hash colliding with any other hash you need 2^64
 *     hashes. This means that to get a collision, on average, you'll need to hash
 *     6 billion files per second for 100 years.
 * </p>
 *
 * @see <a href="http://www.mkyong.com/java/java-md5-hashing-example/">MD5 Checksum</a>
 * @see <a href="http://stackoverflow.com/questions/201705/how-many-random-elements-before-md5-produces-collisions">Collision Odds</a>
 *
 * @author Al Cole
 * @since 1.0
 */
public class DigitalHash {
    private final int FILEIO_BUFFER_SIZE = 8096;

    private MessageDigest mMsgDigest;

    /**
     * Initializes the MD5 message digest subsystem.
     */
    public DigitalHash() {
        try {
            mMsgDigest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            mMsgDigest = null;
        }
    }

    /**
     * Resets the message digest algorithm and empties the internal hash
     * string.  This should be invoked when you wish to restart another
     * hash calculation sequence.
     */
    public void reset() {
        mMsgDigest.reset();
    }

    /**
     * Converts the message digest byte sequence values into a hexadecimal
     * string representation.
     *
     * @return A hexadecimal string.
     */
    public String getHashSequence() {
        byte[] digestBytes;
        StringBuilder hexStrBuilder;

        if (mMsgDigest == null)
            return StringUtils.EMPTY;
        else {
            digestBytes = mMsgDigest.digest();
            hexStrBuilder = new StringBuilder();

            for (byte digestByte : digestBytes) {
                if ((digestByte >= 0) && (digestByte < 16))
                    hexStrBuilder.append("0");
                hexStrBuilder.append(Integer.toHexString(0xFF & digestByte));
            }
            return hexStrBuilder.toString();
        }
    }

    /**
     * Process the contents of the string buffer through the MD5 message
     * digest algorithm.
     *
     * @param aBuffer A string buffer.
     *
     * @throws IOException If the ByteArrayInputStream cannot read the
     * string buffer properly.
     */
    @SuppressWarnings({ "StatementWithEmptyBody" })
    public void processBuffer(String aBuffer) throws IOException {
        if (StringUtils.isNotEmpty(aBuffer))
            mMsgDigest.update(aBuffer.getBytes(StrUtl.CHARSET_UTF_8));
    }

    /**
     * Process the contents of the file through the MD5 message
     * digest algorithm.
     * <p>
     * <b>Note:</b> This method calculates the hash value based
     * on the raw byte in the file (no encoding is performed).
     * </p>
     *
     * @param aFile Representing the file to process.
     *
     * @throws IOException If the FileInputStream cannot read the
     * file properly.
     */
    public void processFile(File aFile) throws IOException {
        int bytesRead;

        FileInputStream fileIS = new FileInputStream(aFile);
        byte[] byteArray = new byte[FILEIO_BUFFER_SIZE];

        while ((bytesRead = fileIS.read(byteArray, 0, FILEIO_BUFFER_SIZE)) != -1)
            mMsgDigest.update(byteArray, 0, bytesRead);

        fileIS.close();
    }

    /**
     * Process the contents of the file through the MD5 message
     * digest algorithm.
     *
     * @param aFileName Identifying the file to process.
     *
     * @throws IOException If the FileInputStream cannot read the
     * file properly.
     */
    public void processFile(String aFileName) throws IOException {
        processFile(new File(aFileName));
    }
}