ImageComparator compares a byte[] for equality by creating 2 hashes for the bytearray and comparing thoose hashes. : Image Filter « 2D Graphics GUI « Java
ImageComparator compares a byte[] for equality by creating 2 hashes for the bytearray and comparing thoose hashes.
/**
*
* JFreeReport : a free Java reporting library
*
*
* Project Info: http://reporting.pentaho.org/
*
* (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
*
* This library is free software; you can redistribute it and/or modify it under the terms
* of the GNU Lesser General Public License as published by the Free Software Foundation;
* either version 2.1 of the License, or (at your option) any later version.
*
* This library 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License along with this
* library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, MA 02111-1307, USA.
*
* [Java is a trademark or registered trademark of Sun Microsystems, Inc.
* in the United States and other countries.]
*
* ------------
* ImageComparator.java
* ------------
* (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
*/
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
/**
* The ImageComparator tries to compare a byte[] for equality by creating 2 hashes for the
* bytearray and comparing thoose hashes. If no digest algorithms are available, then the
* complete byte[] is used for comparison.
* <p>
* Using the digest method trades computing time for space.
*
* @author Thomas Morgner
*/
public class ImageComparator
{
/**
* A ImageCompareData that uses the complete image data for comparison.
*/
private static final class CompleteImageCompareData
{
/**
* The image content.
*/
private final byte[] image;
/**
* Create a new CompleteImageCompareData instance.
*
* @param image the image data used for comparison.
*/
private CompleteImageCompareData (final byte[] image)
{
this.image = image;
}
/**
* Checks whether the given Object equals this object.
*
* @param o the to be compared object
* @return true, if both objects are equal
*/
public boolean equals (final Object o)
{
if (this == o)
{
return true;
}
if (!(o instanceof CompleteImageCompareData))
{
return false;
}
final CompleteImageCompareData data = (CompleteImageCompareData) o;
if (!Arrays.equals(image, data.image))
{
return false;
}
return true;
}
/**
* returns a hashcode for this class.
*
* @return always 0.
*/
public int hashCode ()
{
return image.length;
}
}
/**
* An ImageComparator which uses precomputed Message-Digests to compare the image.
*/
private static final class DigestImageCompareData
{
/**
* An MD5 digest.
*/
private byte[] digestMD5Data;
/**
* An SHA digest.
*/
private byte[] digestSHAData;
/**
* Creates a new DigestImageCompareData instance.
*
* @param digestMD5Data the MD5 digest data
* @param digestSHAData the SHA1 digest data
*/
private DigestImageCompareData (final byte[] digestMD5Data,
final byte[] digestSHAData)
{
if (digestMD5Data == null || digestSHAData == null)
{
throw new NullPointerException();
}
this.digestMD5Data = digestMD5Data;
this.digestSHAData = digestSHAData;
}
/**
* Checks whether the given Object equals this object.
*
* @param o the to be compared object
* @return true, if both objects are equal
*/
public boolean equals (final Object o)
{
if (this == o)
{
return true;
}
if (!(o instanceof DigestImageCompareData))
{
return false;
}
final DigestImageCompareData data = (DigestImageCompareData) o;
if (!Arrays.equals(digestMD5Data, data.digestMD5Data))
{
return false;
}
if (!Arrays.equals(digestSHAData, data.digestSHAData))
{
return false;
}
return true;
}
/**
* returns a hashcode for this class.
*
* @return always 0.
*/
public int hashCode ()
{
return 0;
}
}
/**
* An MD5 message digest.
*/
private MessageDigest digestMD5;
/**
* An SHA message digest.
*/
private MessageDigest digestSHA;
/**
* Creates a new ImageComparator. The comparator checks whether the MD5 and the SHA
* message digest implementations are available. If they are not available, an
* alternative comparison method is used, which is more memory consuming.
*/
public ImageComparator ()
{
try
{
digestMD5 = MessageDigest.getInstance("MD5");
}
catch (NoSuchAlgorithmException nse)
{
System.out.println("No MD5 algorithm available");
}
try
{
digestSHA = MessageDigest.getInstance("SHA");
}
catch (NoSuchAlgorithmException nse)
{
System.out.println("No SHA algorithm available");
}
}
/**
* Creates 2 comparable objects. These objects can be compared for equality.
*
* @param image the image data which should be prepared for comparison
* @param fast whether to prefer the memory intensive faster compare method to the
* digest based comparation. This may result in outofmemory errors on huge
* reports or images.
* @return the prepared image data.
*/
public Object createCompareData (final byte[] image, final boolean fast)
{
if (fast == false && (digestMD5 != null && digestSHA != null))
{
final byte[] dataMD5 = digestMD5.digest(image);
final byte[] dataSHA = digestSHA.digest(image);
if (dataSHA != null && dataMD5 != null)
{
return new DigestImageCompareData(dataMD5, dataSHA);
}
}
return new CompleteImageCompareData(image);
}
}
