/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2006-2008, 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.
*/
package org.geotools.filter.expression;
import org.geotools.util.Converters;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.filter.expression.Expression;
import org.opengis.filter.expression.ExpressionVisitor;
//
/**
* Abstract superclass of these Expression implementations.
* <p>
* Contains additional support for "Expression chaining". This allows
* Expressions to be constructed as a chain of Java commands similar to the use
* of the java collections api.
* </p>
* <p>
* Note: Expression chaining is a simple developer convience, it has no effect
* on the data model exposed by the GeoAPI interfaces.
* </p>
* <p>
* Idea: We may also be able to teach this implementation to make use of
* JXPath to extract "attribute values" from Java Beans, DOM, JDOM in addition
* to the geotools & geoapi FeatureType models. It is a cunning plan - any
* implementation will make use of this abstract base class.
* </p>
*
* @author Jody Garnett
*
*
*
* @source $URL$
*/
public abstract class ExpressionAbstract implements Expression {
/** Subclass should overide, default implementation returns null */
public Object evaluate(Object object) {
return null;
}
/**
* Default implementation delegates handling of context
* conversion to Value utility class.
* <p>
* Subclasses are expected to make use of the Value utility class
* (as the easiest way to provide value morphing in confirmance with
* the Filter specification).
*/
public Object evaluate(Object object, Class context) {
return Converters.convert(evaluate( object ), context);
}
/**
* Helper method for subclasses to reduce null checks
* @param expression
* @param feature
* @return value or null
*/
protected Object eval( Expression expression, SimpleFeature feature ){
if( expression == null || feature == null ) return null;
return expression.evaluate( feature );
}
/**
* Helper method for subclasses to reduce null checks
*
* @param expression
* @param feature
* @return value or null
*/
protected Object eval(org.geotools.filter.Expression expression,
SimpleFeature feature) {
if (expression == null || feature == null)
return null;
return expression.evaluate(feature);
}
}