Chip 1997 October/Chip_1997-10_cd.bin/tema/sybase/powerj/samples.z/URLList.java

Text File | 1996-12-16 | 9KB | 323 lines

/*
 * URLList.java
 *
 *
 * Copyright 1996 Sybase, Inc. All rights reserved.
 */


import java.net.*;
import java.util.*;
import java.io.IOException;


/**
 * URLList stores a list of URLs on the server that will periodically
 * be polled to see if their contents have been modified since the
 * last saved modified date.
 */

public class URLList
//******************
{


    //-------------------------------------------------------------
    // Public Methods
    //-------------------------------------------------------------

    /**
     * Add a URL to the list
     * @param URLStr URL to be added
     */

    public void addURL( String URLStr )
    //*********************************
    {
        // Create a new URL and add it to the list
        // NOTE: Use lower case URL as key for hashtable
        try {
            URL aURL = new URL( URLStr );
            String urlKey = aURL.toString().toLowerCase();
            URLItem newURL = new URLItem( aURL, URLStatus.UNKNOWN );

            synchronized( _list ) {
                _list.put( urlKey, newURL );
            }

        } catch( MalformedURLException e ) {
        }
    }

    /**
     * Poll URLs that are currently stored in the list
     */

    public void pollURLs()
    //********************
    {
        try {
            synchronized( _list ) {
                for( Enumeration e = getElements(); e.hasMoreElements(); ) {
                    URLItem oneItem         = ( URLItem ) e.nextElement();
                    URL url                 = oneItem.getURL();
                    String urlKey           = url.toString().toLowerCase();
                    Date savedDate          = oneItem.getDate();
                    URLConnection urlConn   = url.openConnection();
                    long lastModified       = urlConn.getLastModified();
                    Date newDate            = new Date( lastModified );
                    URLItem newItem         = null;

                    // Check if lastModified dates are unknown.  If so, set the
                    // status to UNKNOWN.  If lastModified dates are known, then
                    // check if URL has been modified since the saved date or if
                    // the dates of last modification are equal; then set the
                    // status to NEW or UNCHANGED, respectively
                    if( savedDate == null || lastModified == 0 ) {
                        newItem = new URLItem( url, null, URLStatus.UNKNOWN );
                    } else if( newDate.after( savedDate ) ) {
                        newItem = new URLItem( url, newDate, URLStatus.NEW );
                    } else if( newDate.equals( savedDate ) ) {
                        newItem = new URLItem( url, newDate, URLStatus.UNCHANGED );
                    }

                    // Replace the old URL
                    _list.put( urlKey, newItem );
                }
            }
        } catch( IOException e ) {
        }
    }

    /**
     * Start the polling thread
     */

    public void startPolling()
    //************************
    {
        // Check if the polling thread is running;
        // start it if it isn't
        if( !_urlPoll.isAlive() ) {
            _urlPoll.setURLList( this );
            _urlPoll.start();
        }
    }


    /*
     * Stop the polling thread
     */

    public void finalize()
    //********************
    {
        if( _urlPoll.isAlive() ) {
            _urlPoll.stop();
        }
    }


    //-------------------------------------------------------------
    // Properties
    //-------------------------------------------------------------

    /**
     * Returns the number of URLs currently stored in the list
     */

    public int getSize()
    //******************
    {
        return _list.size();
    }

    /**
     * Returns an Enumeration of the URLs stored in the list;
     * includes the URLs, last modified date and status
     */

    public Enumeration getElements()
    //******************************
    {
        return _list.elements();
    }

    /**
     * Returns an Enumeration of the URLs stored in the list;
     * includes ONLY the URLs and their status
     */

    public Enumeration getURLs()
    //**************************
    {
        Vector statusList = new Vector();
        synchronized( _list ) {
            for( Enumeration e = getElements(); e.hasMoreElements(); ) {
                URLStatus oneItem       = ( URLStatus ) e.nextElement();
                statusList.addElement( oneItem );
            }
        }

        return statusList.elements();
    }

    /**
     * Returns the polling interval, i.e. time between polls
     */

    public long getPollInterval()
    //***************************
    {
        return _urlPoll.getSleepTime();
    }


    //-------------------------------------------------------------
    // Data
    //-------------------------------------------------------------

    static private Hashtable _list = new Hashtable();
    static private URLPollingThread _urlPoll = new URLPollingThread();
}



/*
 * URLStatus stores a URL and its status since the last poll
 */

class URLStatus
//*************
{
    public static final int NEW       = 1;
    public static final int UNCHANGED = 2;
    public static final int UNKNOWN   = 3;

    //-------------------------------------------------------------
    // Constructor
    //-------------------------------------------------------------

    public URLStatus( URL aURL, int aStatus )
    //***************************************
    {
       _url = aURL;
       _status = aStatus;
    }

    //-------------------------------------------------------------
    // Properties
    //-------------------------------------------------------------

    /*
     * Returns the URL
     */

    public URL getURL()
    //*****************
    {
        return _url;
    }


    /*
     * Returns the status since the last poll of this URL
     */

    public int getStatus()
    //********************
    {
        return _status;
    }

    /*
     * Sets the status of this URL
     */

    public void setStatus( int aStatus )
    //**********************************
    {
        _status = aStatus;
    }


    //-------------------------------------------------------------
    // Data
    //-------------------------------------------------------------

    protected URL _url = null;
    protected int _status = 0;
}



/*
 * URLItem stores a URL, its last modified date, and its status
 * since the last poll
 */

class URLItem extends URLStatus
//*****************************
{

    //-------------------------------------------------------------
    // Constructor
    //-------------------------------------------------------------

    public URLItem( URL aURL, int aStatus )
    //*************************************
    {
        super( aURL, aStatus );
        Date newDate = null;
        try {
            // Determine the last modified date of this URL
            URLConnection urlConnection = aURL.openConnection();
            long lastModified = urlConnection.getLastModified();
            if( lastModified != 0 ) {
                newDate = new Date( lastModified );
                super.setStatus( URLStatus.UNCHANGED );
            }
        } catch( IOException e ) {
        }
        _date = newDate;
    }

    public URLItem( URL aURL, Date aDate, int aStatus )
    //*************************************************
    {
        super( aURL, aStatus );
        _date = aDate;
    }

    //-------------------------------------------------------------
    // Properties
    //-------------------------------------------------------------

    /*
     * Returns the (stored) last modified date of this URL
     */

    public Date getDate()
    //*******************
    {
        return _date;
    }

    /*
     * Sets the last modified date for this URL
     */

    public void setDate( Date aDate )
    //*******************************
    {
        _date = aDate;
    }

    //-------------------------------------------------------------
    // Data
    //-------------------------------------------------------------

    protected Date _date = null;
}