viewsdisplayfactory.java

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//
// This file is part of the OpenNMS(R) Application.
//
// OpenNMS(R) is Copyright (C) 2002-2003 The OpenNMS Group, Inc.  All rights reserved.
// OpenNMS(R) is a derivative work, containing both original code, included code and modified
// code that was published under the GNU General Public License. Copyrights for modified 
// and included code are below.
//
// OpenNMS(R) is a registered trademark of The OpenNMS Group, Inc.
//
// Modifications:
//
// 2003 Jan 31: Cleaned up some unused imports.
//
// Original code base Copyright (C) 1999-2001 Oculan Corp.  All rights reserved.
//
// 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.
//       
// For more information contact: 
//      OpenNMS Licensing       <[e-mail]>
//      http://www.opennms.org/
//      http://www.opennms.com/
//
// Tab Size = 8
//

package org.opennms.netmgt.config;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.exolab.castor.xml.MarshalException;
import org.exolab.castor.xml.Unmarshaller;
import org.exolab.castor.xml.ValidationException;
import org.opennms.netmgt.ConfigFileConstants;
import org.opennms.netmgt.config.viewsdisplay.View;
import org.opennms.netmgt.config.viewsdisplay.Viewinfo;

public class ViewsDisplayFactory {
    /** The singleton instance. */
    private static ViewsDisplayFactory instance;

    /** File path of groups.xml. */
    protected File viewsDisplayFile;

    /** Boolean indicating if the init() method has been called. */
    protected boolean initialized = false;

    /** Timestamp of the viewDisplay file, used to know when to reload from disk. */
    protected long lastModified;

    /** Map of view objects by name. */
    protected Map viewsMap;

    /**
     * Empty private constructor so this class cannot be instantiated outside
     * itself.
     */
    private ViewsDisplayFactory() {
    }

    /** Be sure to call this method before calling getInstance(). */
    public static synchronized void init() throws IOException, FileNotFoundException, MarshalException, ValidationException {
        if (instance == null) {
            instance = new ViewsDisplayFactory();
            instance.reload();
            instance.initialized = true;
        }
    }

    /**
     * Singleton static call to get the only instance that should exist for the
     * ViewsDisplayFactory
     * 
     * @return the single views display factory instance
     * @throws IllegalStateException
     *             if init has not been called
     */
    public static synchronized ViewsDisplayFactory getInstance() {
        if (instance == null) {
            throw new IllegalStateException("You must call ViewDisplay.init() before calling getInstance().");
        }

        return instance;
    }

    /**
     * Parses the viewsdisplay.xml via the Castor classes
     */
    public synchronized void reload() throws IOException, FileNotFoundException, MarshalException, ValidationException {
        this.viewsDisplayFile = ConfigFileConstants.getFile(ConfigFileConstants.VIEWS_DISPLAY_CONF_FILE_NAME);

        InputStream configIn = new FileInputStream(viewsDisplayFile);
        this.lastModified = viewsDisplayFile.lastModified();

        Viewinfo viewInfo = (Viewinfo) Unmarshaller.unmarshal(Viewinfo.class, new InputStreamReader(configIn));
        this.viewsMap = new HashMap();

        Collection viewList = viewInfo.getViewCollection();
        Iterator i = viewList.iterator();

        while (i.hasNext()) {
            View view = (View) i.next();
            this.viewsMap.put(view.getViewName(), view);
        }
    }

    /** Can be null */
    public View getView(String viewName) throws IOException, MarshalException, ValidationException {
        if (viewName == null) {
            throw new IllegalArgumentException("Cannot take null parameters.");
        }

        this.updateFromFile();

        View view = (View) this.viewsMap.get(viewName);

        return view;
    }

    /**
     * Reload the viewsdisplay.xml file if it has been changed since we last
     * read it.
     */
    protected void updateFromFile() throws IOException, MarshalException, ValidationException {
        if (this.lastModified != this.viewsDisplayFile.lastModified()) {
            this.reload();
        }
    }
}