overviewcache.java

java高级使用教程 全书一共分六章

// OverviewCache - a cache for netnews overview entries
//
// Copyright (C) 1996 by Jef Poskanzer <[e-mail]>.  All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
// Visit the ACME Labs Java page for up-to-date versions of this and other
// fine Java utilities: http://www.acme.com/java/

package Acme.Nnrpd;

import java.util.*;
import Acme.LruHashtable;

/// A cache for netnews overview entries.
// <P>
// <A HREF="/resources/classes/Acme/Nnrpd/OverviewCache.java">Fetch the software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>

public class OverviewCache
    {

    private Hashtable groupTimeTable = new Hashtable();
    private LruHashtable groupArtNumTable;

    /// Constructor.
    // @param cacheSize maximum size of the cache
    public OverviewCache( int cacheSize )
	{
	groupArtNumTable = new LruHashtable( cacheSize );
	}

    /// Get the last time we cached entries for this group.
    public long getLastTime( NewsDbGroup group )
	{
	Long time = (Long) groupTimeTable.get( group );
	if ( time == null )
	    return -1;
	return time.longValue();
	}
    
    /// Set the last time we cached entries for this group.
    public void setLastTime( NewsDbGroup group )
	{
	Long time = new Long( System.currentTimeMillis() );
	groupTimeTable.put( group, time );
	}

    /// Get an overview entry by group and number.
    public String[] getEntry( NewsDbGroup group, int artNum )
	{
	return (String[])
	    groupArtNumTable.get( groupArtNumKey( group, artNum ) );
	}

    /// Add an overview entry by group and number.
    public void addEntry( String[] entry, NewsDbGroup group, int artNum )
	{
	groupArtNumTable.put( groupArtNumKey( group, artNum ), entry );
	}

    /// Generate a single hashtable key for the (group,artNum) pair.
    private Integer groupArtNumKey( NewsDbGroup group, int artNum )
	{
	return new Integer( group.getName().hashCode() ^ artNum );
	}

    }