ExampleFunctionFactory2.java

package org.geotools.tutorial.function;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.geotools.filter.FunctionFactory;
import org.geotools.filter.capability.FunctionNameImpl;
import org.opengis.filter.capability.FunctionName;
import org.opengis.filter.expression.Expression;
import org.opengis.filter.expression.Function;
import org.opengis.filter.expression.Literal;

import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.Geometry;

public class ExampleFunctionFactory2 implements FunctionFactory {    
    private ArrayList<FunctionName> functionList;
    private static FunctionName FIRST = new FunctionNameImpl("first","geometry");
    public synchronized List<FunctionName> getFunctionNames() {
        if( functionList == null ){
            functionList = new ArrayList<FunctionName>();
            functionList.add( FIRST );
        }
        return Collections.unmodifiableList( functionList );
    }    
    public Function function(String name, List<Expression> args, Literal fallback) {
        if( "first".equals(name)){
            return new AbstractFunction( FIRST, args, fallback ){
                public Geometry evaluate(Object object) {
                    Geometry geom = eval(object, 0, Geometry.class );
                    Coordinate coordinate = geom.getCoordinate();
                    return geom.getFactory().createPoint(coordinate);
                }
            };
        }
        return null; // we do not implement that function
    }
}