testeetestutils.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.testee.test;
import javax.servlet.http.*;
import javax.servlet.*;

/**
 * TesteeTestUtils is a helper class containing some useful utility methods
 * for conducting testee's tests.
 * 
 * @version $Revision: 1.3 $ at $Date: 2004/03/31 14:16:10 $ by $Author: alexycyap $
 * @author Alexander Yap
 */
public abstract class TesteeTestUtils
{
	private TesteeTestUtils() 
    { 
		// Nothing here
    }
	
	private static final String TEST_TIME_TOKEN_KEY = "testTimeToken";
	private static final String TEST_TIME_TOKEN_SEPARATOR = ":";
	private static final String QUESTION_TIME_TOKEN_KEY = "quesTimeToken";
	private static final String QUESTION_TIME_TOKEN_SEPARATOR = ":";
	
	/**
	 * Stores a token at the start of a test as an attribute of the user session, 
	 * in order to measure the time taken for the test.
	 * @param session User session
	 * @param testId Test Id.
	 */
	static void storeTestTimeToken(HttpSession session, Integer testId)
	{
		session.setAttribute(TEST_TIME_TOKEN_KEY,testId.toString()+TEST_TIME_TOKEN_SEPARATOR+String.valueOf(System.currentTimeMillis()));
	}

	/**
	 * Checks the amount of time taken for a test by comparing the current
	 * time with that stored as the testTimeToken. 
	 * @param session User session
	 * @param testId Test Id
	 * @return Amount of time taken for the test in milliseconds.
	 * @throws ServletException if the testTimeToken is missing.
	 * @throws IllegalArgumentException if the testTimeToken is invalid.
	 * @see #storeTestTimeToken(HttpSession, String)
	 */
	static long checkTestTimeToken(HttpSession session, Integer testId) throws ServletException
	{
		String token = (String)session.getAttribute(TEST_TIME_TOKEN_KEY);
		if (token==null)
		{
			throw new ServletException("Missing session attribute "+TEST_TIME_TOKEN_KEY);
		}
		
		String[] tokenStrs = token.split(TEST_TIME_TOKEN_SEPARATOR);
		if (tokenStrs.length!=2)
		{
			throw new IllegalArgumentException("Invalid value "+token+" in session attribute "+TEST_TIME_TOKEN_KEY);					
		}
		
		if (!testId.equals(new Integer(tokenStrs[0])))
		{
			throw new IllegalArgumentException("Wrong testId token "+tokenStrs[0]+" for in session attribute "+TEST_TIME_TOKEN_KEY);
		}
		
		long tokenTime = -1;
		try
		{
			tokenTime = Long.parseLong(tokenStrs[1]);
		}
		catch (NumberFormatException nfex)
		{
			throw new IllegalArgumentException("Invalid value "+token+" in session attribute "+TEST_TIME_TOKEN_KEY);								
		}
		return System.currentTimeMillis()-tokenTime;
	}
	
	/**
	 * Simply removes the testTimeToken without processing it.
	 * @param session User session.
	 */
	static void removeTestTimeToken(HttpSession session)
	{
		session.removeAttribute(TEST_TIME_TOKEN_KEY);
	}
	
	/**
	 * Stores a token at the start of a question as an attribute of the user session, 
	 * in order to measure the time taken to answer the question as part of a test.
	 * @param session User session
	 * @param testId Test Id.
	 * @param quesId Question Id.
	 */
	static void storeQuestionTimeToken(HttpSession session, Integer testId, Integer quesId)
	{
		session.setAttribute(QUESTION_TIME_TOKEN_KEY,testId+QUESTION_TIME_TOKEN_SEPARATOR+quesId+QUESTION_TIME_TOKEN_SEPARATOR+String.valueOf(System.currentTimeMillis()));
	}
	
	/**
	 * Checks the amount of time taken to answer a question by comparing the current
	 * time with that stored as the questionTimeToken. 
	 * @param session User session
	 * @param testId Test Id
	 * @param quesId Question Id.
	 * @return Amount of time taken to answer the test in milliseconds.
	 * @throws ServletException if the questionTimeToken is missing.
	 * @throws IllegalArgumentException if the questionTimeToken is invalid.
	 * @see #storeQuestionTimeToken(HttpSession, String, String)
	 */
	static long checkQuestionTimeToken(HttpSession session, Integer testId, Integer quesId) throws ServletException
	{
		String token = (String)session.getAttribute(QUESTION_TIME_TOKEN_KEY);
		if (token==null)
		{
			throw new ServletException("Missing session attribute "+QUESTION_TIME_TOKEN_KEY);
		}
		
		String[] tokenStrs = token.split(QUESTION_TIME_TOKEN_SEPARATOR);
		if (tokenStrs.length!=3)
		{
			throw new IllegalArgumentException("Invalid value "+token+" in session attribute "+QUESTION_TIME_TOKEN_KEY);					
		}
		
		if (!testId.equals( new Integer(tokenStrs[0]) ))
		{
			throw new IllegalArgumentException("Wrong testId token "+tokenStrs[0]+" for session attribute "+QUESTION_TIME_TOKEN_KEY);
		}

		if (!quesId.equals( new Integer(tokenStrs[1]) ))
		{
			throw new IllegalArgumentException("Wrong quesId token "+tokenStrs[1]+" for session attribute "+QUESTION_TIME_TOKEN_KEY);
		}
		
		long tokenTime = -1;
		try
		{
			tokenTime = Long.parseLong(tokenStrs[2]);
		}
		catch (NumberFormatException nfex)
		{
			throw new IllegalArgumentException("Invalid value "+token+" in session attribute "+QUESTION_TIME_TOKEN_KEY);								
		}
		return System.currentTimeMillis()-tokenTime;
		
	}

	/**
	 * Simply removes the questionTimeToken without processing it.
	 * @param session User session.
	 */
	static void removeQuestionTimeToken(HttpSession session)
	{
		session.removeAttribute(QUESTION_TIME_TOKEN_KEY);
	}
	
}