Collection_CountFunction.java

/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 * 
 *    (C) 2005-2008, Open Source Geospatial Foundation (OSGeo)
 *    
 *    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;
 *    version 2.1 of the License.
 *
 *    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.
 *
 * Created on May 11, 2005, 6:21 PM
 */
package org.geotools.filter.function;

import static org.geotools.filter.capability.FunctionNameImpl.parameter;

import java.io.IOException;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.geotools.data.simple.SimpleFeatureCollection;
import org.geotools.feature.visitor.CalcResult;
import org.geotools.feature.visitor.CountVisitor;
import org.geotools.filter.FunctionExpressionImpl;
import org.geotools.filter.IllegalFilterException;
import org.geotools.filter.capability.FunctionNameImpl;
import org.opengis.filter.capability.FunctionName;

/**
 * Calculates the count value of an attribute for a given SimpleFeatureCollection and
 * Expression.
 * 
 * @author Cory Horner
 * @since 2.2M2
 *
 * @source $URL$
 */
public class Collection_CountFunction extends FunctionExpressionImpl{
	/** The logger for the filter module. */
	private static final Logger LOGGER = org.geotools.util.logging.Logging.getLogger("org.geotools.filter.function");

	SimpleFeatureCollection previousFeatureCollection = null;

	Object count = null;

    // public static FunctionName NAME = new FunctionNameImpl("Collection_Count","expression");
    public static FunctionName NAME = new FunctionNameImpl("Collection_Count",
            parameter( "count", Object.class),
            parameter("expression", Object.class));
	
	/**
	 * Creates a new instance of Collection_CountFunction
	 */
	public Collection_CountFunction() {
	    super(NAME);
	}

	public int getArgCount() {
		return 1;
	}

	/**
	 * Calculate count (using FeatureCalc) - only one parameter is used.
	 * 
	 * @param collection
	 *            collection to calculate the count
	 * 
	 * @return An object containing the count value of the attributes
	 * 
	 * @throws IllegalFilterException
	 * @throws IOException
	 */
	static CalcResult calculateCount(SimpleFeatureCollection collection)
			throws IllegalFilterException, IOException {
		CountVisitor countVisitor = new CountVisitor();
		collection.accepts(countVisitor, null);
		return countVisitor.getResult();
	}

	/**
	 * The provided arguments are evaulated with respect to the
	 * FeatureCollection.
	 * 
	 * <p>
	 * For an aggregate function (like count) please use the WFS mandated XPath
	 * syntax to refer to featureMember content.
	 * </p>
	 * 
	 * <p>
	 * To refer to all 'X': <code>featureMember/asterisk/X</code>
	 * </p>
	 * 
	 * @param args
	 *            DOCUMENT ME!
	 * 
	 * @throws IllegalArgumentException
	 *             DOCUMENT ME!
	 */
    public void setParameters(List args) {
        // if we see "featureMembers/*/ATTRIBUTE" change to "ATTRIBUTE"
        org.opengis.filter.expression.Expression expr = (org.opengis.filter.expression.Expression) args.get(0);
        expr = (org.opengis.filter.expression.Expression) expr.accept(new CollectionFeatureMemberFilterVisitor(),null);
        args.set(0, expr );
        super.setParameters(args);
    }

	public Object evaluate(Object feature) {
		if (feature == null) {
			return new Integer(0); // no features were visited in the making of this answer
		}
		SimpleFeatureCollection featureCollection = (SimpleFeatureCollection) feature;
		synchronized (featureCollection) {
			if (featureCollection != previousFeatureCollection) {
				previousFeatureCollection = featureCollection;
				count = null;
				try {
					CalcResult result = calculateCount(featureCollection);
					if (result != null) {
						count = result.getValue();
					}
				} catch (IllegalFilterException e) {
					LOGGER.log(Level.FINER, e.getLocalizedMessage(), e);
				} catch (IOException e) {
					LOGGER.log(Level.FINER, e.getLocalizedMessage(), e);
				}
			}
		}
		return count;
	}

}