/**
 *
 */
package de.intevation.gnv.geobackend.base.query;

import org.apache.log4j.Logger;

/**
 * @author Tim Englich <tim.englich@intevation.de>
 *
 */
public class QueryExecutorFactory {

    public static final String QUERY_EXECUTOR_FACTORY = "query.executor.factory";
    
    /**
     * the logger, used to log exceptions and additonaly information
     */
    private static Logger log = Logger.getLogger(QueryExecutorFactory.class);

    
    /**
     * The singleton Instance of this Factory.
     */
    private static QueryExecutorFactory instance = null;

    /**
     * Basic-Constructor of this Class
     */
    public QueryExecutorFactory() {
        super();
    }

    /**
     * This Method provides an singleton Instance of this Class.
     * @return an singleton Instance of this Class
     */
    public static synchronized QueryExecutorFactory getInstance(){
        if (instance == null) {
            String className = System.getProperty(QUERY_EXECUTOR_FACTORY);
            if (className != null) {
                try {
                    Class clazz = Class.forName(className);
                    instance = (QueryExecutorFactory)clazz.newInstance();
                    return instance;
                }
                catch (ClassNotFoundException cnfe) {
                    log.error(cnfe);
                }
                catch (InstantiationException ie) {
                    log.error(ie);
                }
                catch(IllegalAccessException iae) {
                    log.error(iae);
                }
                catch (ClassCastException cce) {
                    log.error(cce);
                }
            }

            instance = new QueryExecutorFactory();
        }
        return instance;
    }
    
    
    /**
     * Getting the QueryExecutor
     * @return the QueryExecutor
     */
    public QueryExecutor getQueryExecutor(){
        return new DefaultQueryExceutor();
    }
}