resultsetdatarowreader.java

著名的开源仿真软件yale

/*
 *  YALE - Yet Another Learning Environment
 *  Copyright (C) 2002, 2003
 *      Simon Fischer, Ralf Klinkenberg, Ingo Mierswa, 
 *          Katharina Morik, Oliver Ritthoff
 *      Artificial Intelligence Unit
 *      Computer Science Department
 *      University of Dortmund
 *      44221 Dortmund,  Germany
 *  email: [e-mail]
 *  web:   http://yale.cs.uni-dortmund.de/
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License as 
 *  published by the Free Software Foundation; either version 2 of the
 *  License, or (at your option) any later version. 
 *
 *  This program 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
 *  General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 *  USA.
 */
package edu.udo.cs.yale.example;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import edu.udo.cs.yale.example.Example;
import edu.udo.cs.yale.example.Attribute;
import edu.udo.cs.yale.tools.LogService;
import edu.udo.cs.yale.example.ExampleReader;

/**
 * Unlike a {@link FileDataRowReader} that reads examples from a file,
 * objects of this class read examples from a {@link ResultSet}, a data
 * structure that is returned from a database query.
 *
 * @see edu.udo.cs.yale.tools.DatabaseHandler
 * @see edu.udo.cs.yale.operator.DatabaseExampleSource
 * @see edu.udo.cs.yale.operator.KDBExampleSource
 * @version $Id: ResultSetDataRowReader.java,v 2.2 2003/06/03 20:49:00 fischer Exp $
 */
public class ResultSetDataRowReader extends AbstractDataRowReader {

    private Attribute[] attributes;
    private ResultSet resultSet;

    private static final int DONT_KNOW_YET = 0;
    private static final int YES           = 1;
    private static final int NO            = 2;

    private int hasNext = DONT_KNOW_YET;

    /**
     * Constructor.
     *
     * @param attributeList List of attributes
     * @param resultSet A ResultSet as returned from a database query
     */
    public ResultSetDataRowReader(DataRowFactory dataRowFactory,
				  List attributeList,
				  ResultSet resultSet) {
	super(dataRowFactory);
	this.resultSet = resultSet;
	this.attributes = new Attribute[attributeList.size()];
	attributeList.toArray(this.attributes);
    }


    public boolean hasNext() {
	switch (hasNext) {
	case YES: return true;
	case NO: return false;
	case DONT_KNOW_YET:
	    try {
		if (resultSet.next()) {
		    hasNext = YES;
		    return true;
		} else {
		    hasNext = NO;
		    resultSet.close();
		    return false;
		}
	    } catch (SQLException e) {
		LogService.logException("While reading examples from result set:", e);
		return false;
	    }
	default:
	    // impossible
	    return false;
	}
    }

    public DataRow next() {
        if (hasNext()) {
	    hasNext = DONT_KNOW_YET;
	    try {
		//Object[] data = new Object[resultSet.getMetaData().getColumnCount()];
		//String[] data = new String[resultSet.getMetaData().getColumnCount()];
		double[] data = new double[resultSet.getMetaData().getColumnCount()];
		DataRow row = getFactory().create(attributes.length);
		for (int i = 0; i < data.length; i++) {
		    //data[i] = resultSet.getString(i + 1); // column numbers in resultSet start with 1
		    //data[i] = resultSet.getObject(i + 1); // column numbers in resultSet start with 1
		    row.set(attributes[i], DatabaseDataRow.readColumn(resultSet, attributes[i]));
		}
		//return getFactory().create(data, attributes);
		return row;
	    } catch (SQLException sqle) {
		throw new RuntimeException("Error accessing the result of a query:" + sqle.toString());  
	    }
        } else { 
	    return null;  
	}
    } 
}