dataconnection.java

来自「java实现浏览器等本地桌面的功能」· Java 代码 · 共 166 行

/*
 * $Id: DataConnection.java,v 1.3 2005/10/10 17:01:00 rbair Exp $
 *
 * Copyright 2005 Sun Microsystems, Inc., 4150 Network Circle,
 * Santa Clara, California 95054, U.S.A. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

package org.jdesktop.dataset;

import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Maintains a connection to some underlying data store. Generally used by
 * a DataProvider to interact with the DataStore, however, it is not specifically
 * necessary for a DataProvider to use a DataConnection.
 *
 * @author rbair
 */
public abstract class DataConnection {
	/**
	 * Logger used for log statements
	 */
	private static final Logger LOG = Logger.getLogger(DataConnection.class.getName());

	/**
     * Helper used for notifying of bean property changes. In particular, this
     * is used to notify of changes in the connection status
     */
    private PropertyChangeSupport pcs = new PropertyChangeSupport(this);

    /**
     * Flag indicating the logical connection status of this DataConnection.
     * It is possible for the DataConnection to be logically connected but
     * physically disconnected (ie HTTP), or vice versa.
     */
    private boolean connected = false;
    
    /**
     * Manages the connected state of this DataConnection. The connected
     * state is this DataConnections "logical" connection status. The
     * underlying connection may be disconnected, and yet the
     * DataConnection may still be "logically" connected. For example, an
     * HTTP based connection may not be persistent, but is always "logically"
     * connected.
     * <p/>
     * It is possible for listeners to be attached to the DataConnection that
     * can react to the connection status. For instance, a status bar icon might
     * change to indicate its disconnected status. Or DataSets could be flushed
     * of their data.
     * @param b If true, opens any necessary connections to the source.
     *          For instance, this could be used to open a connection to a
     *          database, or to a URL. If false, then any current connections
     *          are logically closed, and may be physically closed, depending
     *          on the DataConnection implementation
     * @throws IOException
     */
    public void setConnected(boolean b) {
        if (b && !connected) {
            try {
            	LOG.fine("Attempting to connect to the data store");
                connect();
                connected = true;
                LOG.fine("Connected to the data store, firing property change event");
                pcs.firePropertyChange("connected", false, true);
            } catch (Exception e) {
            	LOG.log(Level.SEVERE, "Failed to connect to the data store.", e);
            	//no need to fire a property change event here, because connected was
            	//false when this method began
                connected = false;
            }
        } else if (!b && connected) {
            try {
            	LOG.fine("Attempting to disconnect from the data store");
                disconnect();
            } catch (Exception e) {
            	LOG.log(Level.WARNING, "Failed to physically disconnect from the data store, " +
            			"but will continue to logically disconnect from the data store.", e);
                e.printStackTrace();
            } finally {
                connected = false;
                LOG.fine("Logically disconnected from the data store, firing property change event");
                pcs.firePropertyChange("connected", true, false);
            }
        }
    }
    
    /**
     * @return whether the DataStoreConnection is logically connected or not.
     */
    public boolean isConnected() {
        return connected;
    }
    
    /**
     * Optional method to make a connection to the data store. This method is
     * called whenever the connection state changes from !connected to
     * connected. It is up to the child class implementation to manage the
     * physical connection to the data store. This method may or may not be
     * useful in that context.
     * 
     * @throws Exception
     */
    protected abstract void connect() throws Exception;

    /**
     * Optional method to disconnect from the data store. This method is called
     * whenever the connection state changes from connected to !connected. It is
     * up to the child class implementation to manage the physical connection to
     * the data store. This method may or may not be useful in that context.
     * 
     * @throws Exception
     */
    protected abstract void disconnect() throws Exception;
    
    /**
     * Adds a PropertyChangeListener to this class for any changes to bean 
     * properties.
     *
     * @param listener The PropertyChangeListener to notify of changes to this 
     * instance.
     */
    public void addPropertyChangeListener(PropertyChangeListener listener) {
        pcs.addPropertyChangeListener(listener);
    }

   /**
     * Adds a PropertyChangeListener to this class for specific property changes.
     *
     * @param propertyName The name of the property to listen to changes for.
     * @param listener The PropertyChangeListener to notify of changes to this 
     * instance.
     */
     public void addPropertyChangeListener(String propertyName,
            PropertyChangeListener listener) {
        pcs.addPropertyChangeListener(propertyName, listener);
    }
    
    /**
     * Stops notifying a specific listener of changes to a specific property.
     *
     * @param propertyName The name of the property to ignore from now on.
     * @param listener The listener to stop receiving notifications.
     */
    public void removePropertyChangeListener(String propertyName, PropertyChangeListener listener) {
    	pcs.removePropertyChangeListener(propertyName, listener);
    }

}