like.java

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/*  Sesame - Storage and Querying architecture for RDF and RDF Schema
 *  Copyright (C) 2001-2005 Aduna
 *
 *  Contact: 
 *  	Aduna
 *  	Prinses Julianaplein 14 b
 *  	3817 CS Amersfoort
 *  	The Netherlands
 *  	tel. [phone]
 *  	fax. [phone]
 *
 *  	http://aduna.biz/
 *  	http://www.openrdf.org/
 *  
 *  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
 */

package org.openrdf.sesame.query.rql.model;

import org.openrdf.model.Literal;
import org.openrdf.model.Value;

import org.openrdf.sesame.query.QueryEvaluationException;
import org.openrdf.sesame.sail.RdfSchemaSource;
import org.openrdf.sesame.sail.ValueIterator;

public class Like implements BooleanQuery {

/*-------------------------------------------+
| Variables                                  |
+-------------------------------------------*/

	protected ResourceQuery _arg1;
	protected StringConstant _arg2;

/*-------------------------------------------+
| Constructors                               |
+-------------------------------------------*/

	public Like(ResourceQuery arg1, StringConstant arg2) {
		_arg1 = arg1;
		_arg2 = arg2;
	}

/*-------------------------------------------+
| Methods                                    |
+-------------------------------------------*/

	/**
	 * Determines whether the two operands match according to the
	 * <code>like</code> operator. The operator is defined as a string
	 * comparison with the possible use of an asterisk (*) at the end
	 * and/or the start of the second operand to indicate substring
	 * matching.
	 *
	 * @param rss the repository abstraction layer which is to be queried
	 * during evaluation.
	 *
	 * @return <code>true</code> if the operands match according to the
	 * <code>like</code> operator, <code>false</code> otherwise.
	 * @throws QueryEvaluationException when the first argument is a set
	 * (instead of a single value), or when it is not instantiated.
	 **/
	public boolean isTrue(RdfSchemaSource rss) throws QueryEvaluationException {
		ValueIterator iter1;
		Value val;
        String stringVal;

		if (_arg1.returnsSet()) {
			throw new QueryEvaluationException(
					"Cannot compare a set to a string : " +
					this.toString());
		}

		iter1 = _arg1.getResources(rss);
		if (iter1 == null) {
			throw new QueryEvaluationException(
					_arg1.toString() + " has no assigned value. ");
		}
		
		// everything is peachy

		val = iter1.next();
		iter1.close();
        
        if (val instanceof org.openrdf.model.URI) {
            stringVal = ((org.openrdf.model.URI)val).getURI();
        }
        else if (val instanceof Literal) {
            stringVal = ((Literal)val).getLabel();
        }
		else {
			// Intersections or BNodes cannot be compared to a string pattern
			return false;
		}

		return _like(stringVal, _arg2.getValue());
	}

	protected boolean _like(String val, String pattern) {
		int valIndex = 0;
		int prevPatternIndex = -1;
		int patternIndex = pattern.indexOf('*');

		if (patternIndex == -1) {
			// No wildcards
			return val.equalsIgnoreCase(pattern);
		}

		// Convert both strings to lower case
		val = val.toLowerCase();
		pattern = pattern.toLowerCase();

		String snippet;

		if (patternIndex > 0) {
			// Pattern does not start with a wildcard, first part must match
			snippet = pattern.substring(0, patternIndex);
			if (!val.startsWith(snippet)) {
				return false;
			}

			valIndex += snippet.length();
			prevPatternIndex = patternIndex;
			patternIndex = pattern.indexOf('*', patternIndex + 1);
		}

		while (patternIndex != -1) {
			// Get snippet between previous wildcard and this wildcard
			snippet = pattern.substring(prevPatternIndex + 1, patternIndex);

			// Search for snippet
			valIndex = val.indexOf(snippet, valIndex);
			if (valIndex == -1) {
				return false;
			}

			valIndex += snippet.length();
			prevPatternIndex = patternIndex;
			patternIndex = pattern.indexOf('*', patternIndex + 1);
		}

		// Part after last wildcard
		snippet = pattern.substring(prevPatternIndex + 1);

		if (snippet.length() > 0) {
			// Pattern does not end with a wildcard.

			// Search last occurence of the snippet.
			valIndex = val.indexOf(snippet, valIndex);
			int i;
			while ((i = val.indexOf(snippet, valIndex + 1)) != -1) {
				// A later occurence was found.
				valIndex = i;
			}

			if (valIndex == -1) {
				return false;
			}

			valIndex += snippet.length();

			if (valIndex < val.length()) {
				// Some characters were not matched
				return false;
			}
		}

		return true;
	}

	public String getQuery() {
		return this.toString();
	}

	public String toString() {
		return _arg1.toString() + " like " + _arg2.toString();
	}
}