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a Java JDBC driver for reading comma-separated-value files
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/*
 *  CsvJdbc - a JDBC driver for CSV files
 *  Copyright (C) 2001  Jonathan Ackerman
 *  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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.relique.jdbc.csv;

import java.util.Hashtable;
import java.util.StringTokenizer;
import java.util.regex.Pattern;

/**
 * Performs string matching for SQL LIKE patterns.
 */
public class LikePattern
{
	public static final String DEFAULT_ESCAPE_STRING = "\\";

	/**
	 * Global lookup table of LIKE pattern to compiled regular expression.
	 */
	private static Hashtable compiledRegexs = new Hashtable<>();

	/**
	 * 
	 * @param likePattern an SQL LIKE pattern including % and _ characters.
	 * @param escape SQL ESCAPE character, or empty string for no escaping.
	 * @param input string to be matched.
	 * @return true if input string matches LIKE pattern.
	 */
	public static boolean matches(String likePattern, String escape, CharSequence input)
	{
		boolean retval;
		int percentIndex = likePattern.indexOf('%');
		int underscoreIndex = likePattern.indexOf('_');
		if (percentIndex < 0 && underscoreIndex < 0)
		{
			/*
			 * No wildcards in pattern so we can just compare strings.
			 */
			retval = likePattern.equals(input);
		}
		else
		{
			Pattern p = compiledRegexs.get(likePattern);
			if (p == null)
			{
				/*
				 * First convert LIKE pattern to a regular expression.
				 */
				boolean isEscaped = false;
				StringBuilder regex = new StringBuilder();
				StringTokenizer tokenizer = new StringTokenizer(likePattern, "%_" + escape, true);
				while (tokenizer.hasMoreTokens())
				{
					String token = tokenizer.nextToken();
					if (token.equals(escape))
					{
						if (isEscaped)
						{
							/*
							 * Two escaped characters in a row result match a
							 * single literal escape character.
							 */
							regex.append(Pattern.quote(token));
						}
						else
						{
							isEscaped = true;
						}
					}
					else
					{
						if (isEscaped)
							regex.append(Pattern.quote(token));
						else if (token.equals("%"))
							regex.append(".*");
						else if (token.equals("_"))
							regex.append(".");
						else
							regex.append(Pattern.quote(token));
						isEscaped = false;
					}
				}

				/*
				 * Cache compiled regular expression because we will probably be
				 * using the same one again and again.
				 *
				 * DOTALL flag required so that dots in regular expression match
				 * any newline character in input string.
				 */
				p = Pattern.compile(regex.toString(), Pattern.DOTALL);
				compiledRegexs.put(likePattern, p);
			}
			retval = p.matcher(input).matches();
		}
		return retval;
	}
}