schoolconfig.java

老外的在线考试

/*
 * SchoolEJB - CyberDemia's library of EJBs for educational related services.
 * Copyright (C) 2003 CyberDemia Research and Services
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; 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 library for complete text of license.
 */
package com.cyberdemia.school;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.*;
import com.cyberdemia.xml.XMLUtil;
import com.cyberdemia.school.impl.*;
import java.net.*;
import java.io.InputStream;
import javax.ejb.EJBException;
import java.util.*;

/**
* SchoolConfig is a reader and parser for the School module configuration file.
* It expects to find the <i>school-config.xml</i> configuration file in the directory 
* specified by in the getInstance() method.
* 
* @author Alexander Yap
*/
public class SchoolConfig
{
	/**
	 * Initializes the SchoolConfig with a URL to the school-config.xml.
	 * This method must be called before calling getInstance().
	 * 
	 * @param configURL Configuration URL pointing to school-config.xml, or null if already configured.
	 */
	public static synchronized void init(URL configURL)
	{
		s_instance = new SchoolConfig(configURL);
	}
	
	/**
	* Gets singleton instance of SchoolConfig.
	* This method may only be called after calling init(URL).
	*
	* @return SchoolConfig instance.
	* @see #init(URL)
	*/
	public static synchronized SchoolConfig getInstance()
	{
		return s_instance;
	}
	
	/**
	* Gets the top level hierarchy root node as described in the
	* School module configuration file.
	* @return IHierarchy instance.
	*/
	public IHierarchy getHierarchyRoot()
	{
		return m_hierarchyRoot;
	}

	/**
	* Creates SchoolConfig and configures it using a URL to school.xml.
	* This is private for internal use only.
	* @param configDir Configuration URL pointing to school.xml.
	*/
	private SchoolConfig(URL configURL)
	{
		m_context = "Parsing "+configURL;
		HttpURLConnection connection = null;
		int responseCode;
		try
		{
			assert configURL!=null :
				"Error: Missing configuration URL.";
			connection = (HttpURLConnection)configURL.openConnection();
			responseCode = connection.getResponseCode();
		}
		catch (Exception ex)
		{
			throw new EJBException("Error creating SchoolConfig", ex);
		}
		if (responseCode != HttpURLConnection.HTTP_OK)
			throw new EJBException("Error connecting to "+configURL);
		try
		{
			parseConfig(connection.getInputStream());
		}
		catch (Exception ex)
		{
			throw new EJBException("Error parsing "+configURL,ex);
		}
	}
	
	private void parseConfig(InputStream stream) throws Exception
	{
		DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
		DocumentBuilder db = dbf.newDocumentBuilder();
		Document doc = db.parse( stream );
		Element schoolConfigElem = doc.getDocumentElement();
		assert schoolConfigElem!=null : "Missing root element";
		parseSchoolConfigElement( schoolConfigElem );			
	}

	private void parseSchoolConfigElement(Element configElem) throws Exception
	{
		assert configElem.getNodeName().equals("school-config") :
			"Invalid element "+configElem.getNodeName()+", expecting school-config.";
	
		Element templateElem = XMLUtil.getSingleElement(configElem, "template", m_context);
		parseTemplateElement(templateElem);
	
		Element hierarchyElem = XMLUtil.getSingleElement(configElem, "hierarchy", m_context);
		parseHierarchyElement(hierarchyElem);
	}

	private void parseTemplateElement(Element templateElem) throws Exception
	{
		assert templateElem.getNodeName().equals("template") :
			"Invalid element "+templateElem.getNodeName()+", expecting template.";
		Element[] nodeElems = XMLUtil.getChildElements(templateElem, "node", m_context);
		m_maxLevel = -1;
		for (int n=0; n<nodeElems.length; n++)
		{
			Element nodeElem = nodeElems[n];
			Integer level = new Integer(nodeElem.getAttribute("level"));
			m_hierarchyTemplateMap.put( level, nodeElem.getAttribute("name") );
			if (level.intValue()>m_maxLevel)
			{
				m_maxLevel = level.intValue();
			}
		}
	}
	
	private void parseHierarchyElement(Element hierElem) throws Exception
	{
		assert hierElem.getNodeName().equals("hierarchy") :
			"Invalid element "+hierElem.getNodeName()+", expecting hierarchy.";
		Element rootNodeElem = XMLUtil.getSingleElement(hierElem, "node", m_context);
		m_hierarchyRoot = parseHierarchyNodeElement(rootNodeElem, null, 0);
	}

	private IHierarchy parseHierarchyNodeElement(Element nodeElem, IHierarchy parentNode, int level) throws Exception
	{
		assert nodeElem.getNodeName().equals("node") :
			"Invalid element "+nodeElem.getNodeName()+", expecting node.";
		IHierarchy node = new HierarchyNode(
			XMLUtil.getIntAttribute(nodeElem,"id",m_context),
			XMLUtil.getStringAttribute(nodeElem, "name", m_context),
			(String)m_hierarchyTemplateMap.get(new Integer(level)),
			level, parentNode, level==m_maxLevel );
		if (parentNode!=null)
		{
			parentNode.addChild(node);
		}
		
		Element[] childElems = XMLUtil.getChildElements(nodeElem,"node",m_context);
		for (int c=0; c<childElems.length; c++)
		{
			parseHierarchyNodeElement( childElems[c], node, level+1);	
		}
			
		return node;
	}

	private String m_context = null;
	private IHierarchy m_hierarchyRoot = null;
	private Map m_hierarchyTemplateMap = new HashMap();
	private int m_maxLevel = -1;

	/** Singleton instance. */
	private static SchoolConfig s_instance = null;

}