getcachedchartaction.java

老外的在线考试

/*
 * CyberTester - J2EE Web application for creating, delivering and managing tests/exams/surveys. 
 * Copyright (C) 2004 CyberDemia Research and Services Pty Ltd
 *
 * 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 (see the file COPYING); if not, write to the
 * Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * See the COPYING file located in the top-level-directory of
 * the archive of this program for complete text of license.
 */
package com.cyberdemia.cybertester.common;

import javax.servlet.http.*;
import org.apache.struts.action.*;
import java.util.logging.*;
import java.util.Map;
import com.cyberdemia.cybertester.*;

/**
 * GetCachedChartAction is a Struts action to retrieve a chart 
 * from the chartsCache (stored in user session) and write it to the
 * response's output stream. It is used to delivered a previously created
 * chart to the client.
 * By default, the chart is removed from the chartsCache as soon as it is
 * retrieved in order to minimize memory usage. However, if parameter 
 * "retainChart" is set to true, the chart is kept in the chartsCache.
 * 
 * @version $Revision: 1.2 $ at $Date: 2004/03/15 09:51:51 $ by $Author: alexycyap $
 * @author Alexander Yap
 */
public class GetCachedChartAction extends AbstractUserAction
{
	protected ActionForward doPerform(
		ActionMapping mapping, ActionForm form,
		HttpServletRequest request, HttpServletResponse response,
		HttpSession session) throws Exception
	{
		Logger logger = CyberTesterUtils.getLogger();
		String chartId = CyberTesterUtils.getParameterOrRequestAttribute(request, Constants.CHART_ID_KEY);
		if (chartId==null)
		{
			logger.log(Level.SEVERE, "Missing parameter "+Constants.CHART_ID_KEY);
			return null;
		}

		boolean retainCache = Boolean.valueOf( CyberTesterUtils.getParameterOrRequestAttribute(request, "retainChart") ).booleanValue(); 
		
		Map chartsCache = (Map)session.getAttribute(Constants.CHARTS_CACHE_KEY);		
		ChartDataCache cache = (ChartDataCache)chartsCache.get(chartId);
		if (cache==null)
		{
			logger.log(Level.SEVERE, "Missing chart cache data");
			return null;
		}
		logger.fine("Retrieved chart "+chartId+" from cache.");
		if (!retainCache)
		{
			logger.fine("Removing chart "+chartId+" from cache.");
			chartsCache.remove(chartId);
		}	
		response.getOutputStream().write( cache.data );		
		return null;
	}
	

}