multiplexnewsdb.java

java高级使用教程 全书一共分六章

// MultiplexNewsDb - proxy netnews database
//
// 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.io.*;
import java.util.*;
import java.net.*;
import Acme.Utils;

/// Multiplex netnews database.
// <P>
// This is a news database that forwards requests to different sub-databases
// based on the group name.
// <P>
// <A HREF="/resources/classes/Acme/Nnrpd/MultiplexNewsDb.java">Fetch the software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>

public class MultiplexNewsDb extends NewsDb
    {

    private Vector groupsPats = new Vector();
    private Vector newsDbs = new Vector();

    /// The standard overview.fmt.  Only if all sub-DBs implement this
    // identical format do we do overviewing.
    private static String[] overviewFmt = {
	"Subject", "From", "Date", "Message-ID", "References", "Bytes",
	"Lines" };

    /// Constructor.
    // @exception NewsDbException if something goes wrong
    public MultiplexNewsDb() throws NewsDbException
	{
	}
    
    /// Add a sub-database for a given pattern of groups.
    public void add( String groupsPat, NewsDb newsDb )
	{
	groupsPats.addElement( groupsPat );
	newsDbs.addElement( newsDb );
	}

    /// Attempt authorization.
    // @exception NewsDbException if something goes wrong
    public boolean authorize( String user, String password ) throws NewsDbException
	{
	// If authorization succeeds for all sub-dbs, we return ok.
	for ( int i = 0; i < newsDbs.size(); ++i )
	    {
	    NewsDb newsDb = (NewsDb) newsDbs.elementAt( i );
	    if ( ! newsDb.authorize( user, password ) )
		return false;
	    }
	return true;
	}

    /// Whether posting is allowed.
    // @exception NewsDbException if something goes wrong
    public boolean getPostingOk() throws NewsDbException
	{
	// This is a guess, really - if posting is ok for any sub-db, we
	// return ok.
	for ( int i = 0; i < newsDbs.size(); ++i )
	    {
	    NewsDb newsDb = (NewsDb) newsDbs.elementAt( i );
	    if ( newsDb.getPostingOk() )
		return true;
	    }
	return false;
	}

    /// Get a group by name.
    // @exception NewsDbException if something goes wrong
    public NewsDbGroup getGroup( String groupName ) throws NewsDbException
	{
	NewsDb newsDb = findNewsDb( groupName );
	return newsDb.getGroup( groupName );
	}

    /// Get an article by group and number.
    // @exception NewsDbException if something goes wrong
    public NewsDbArticle getArticle( NewsDbGroup group, int artNum ) throws NewsDbException
	{
	for ( int i = 0; i < newsDbs.size(); ++i )
	    {
	    NewsDb newsDb = (NewsDb) newsDbs.elementAt( i );
	    if ( newsDb.getDbStamp() == group.getDbStamp() )
		return newsDb.getArticle( group, artNum );
	    }
	return null;
	}

    /// Get an article by message-id.
    // @exception NewsDbException if something goes wrong
    public NewsDbArticle getArticle( String messageId ) throws NewsDbException
	{
	// This is an even more expensive operation than usual in the
	// multiplexing database.  Since the dispatching is by group name
	// but you don't have a group name, you have to try each sub-db.
	for ( int i = 0; i < newsDbs.size(); ++i )
	    {
	    NewsDb newsDb = (NewsDb) newsDbs.elementAt( i );
	    NewsDbArticle article = newsDb.getArticle( messageId );
	    if ( article != null )
		return article;
	    }
	return null;
	}

    /// Get specified headers from a range of articles by group and number.
    // Some implementations have special faster methods for getting
    // headers from articles, e.g. an XOVER command to a remote server
    // or a local overview database.  If no such fast method is available,
    // this returns null and the caller should fall back on conventional
    // means.
    // @exception NewsDbException if something goes wrong
    public String[][] getHeaders( String[] names, NewsDbGroup group, int firstArtNum, int lastArtNum ) throws NewsDbException
	{
	NewsDb newsDb = findNewsDb( group.getName() );
	return newsDb.getHeaders( names, group, firstArtNum, lastArtNum );
	}

    /// Get an enumeration of all the groups.
    // @exception NewsDbException if something goes wrong
    public Enumeration getGroups() throws NewsDbException
	{
	return new MultiplexNewsDbGroups( newsDbs.elements() );
	}

    /// Get an enumeration of all groups created after a given time.
    // @exception NewsDbException if something goes wrong
    public Enumeration getGroups( long since ) throws NewsDbException
	{
	return new MultiplexNewsDbGroups( newsDbs.elements(), since );
	}

    /// Get an enumeration of all groups created after a given time that match
    // a given distributions pattern.
    // @exception NewsDbException if something goes wrong
    public Enumeration getGroups( long since, String distsPat ) throws NewsDbException
	{
	return new MultiplexNewsDbGroups( newsDbs.elements(), since, distsPat );
	}

    /// Get an enumeration of all message-ids received after a given time
    // in groups matching the given pattern.
    // @exception NewsDbException if something goes wrong
    public Enumeration getMessageIds( String groupsPat, long since ) throws NewsDbException
	{
	return new MultiplexNewsDbMessageIds( newsDbs.elements(), groupsPat, since );
	}

    /// Get an enumeration of all message-ids received after a given time
    // in groups matching the given pattern, that also match the
    // given distributions pattern.
    // @exception NewsDbException if something goes wrong
    public Enumeration getMessageIds( String groupsPat, long since, String distsPat ) throws NewsDbException
	{
	return new MultiplexNewsDbMessageIds( newsDbs.elements(), groupsPat, since, distsPat );
	}


    /// Post an article.
    // @exception NewsDbException if something goes wrong
    public void post( String text ) throws NewsDbException
	{
	// Find the newsgroups line in the article and parse it to
	// find a group, then post to the right db for that group.
	String newsgroups = NewsDbArticle.getHeader( text, "Newsgroups" );
	if ( newsgroups == null || newsgroups.length() == 0 )
	    throw new NewsDbException( "article has no newsgroups" );
	StringTokenizer st = new StringTokenizer( newsgroups, "," );
	while ( st.hasMoreTokens() )
	    {
	    String groupName = st.nextToken();
	    NewsDb newsDb;
	    try
		{
		newsDb = findNewsDb( groupName );
		}
	    catch ( NewsDbException e )
		{
		// Try another group.
		continue;
		}
	    newsDb.post( text );
	    return;
	    }
	throw new NewsDbException(
	    "can't find a news database supporting any group in " +
	    newsgroups );
	}

    /// Shut down the news database.
    public void close()
	{
	for ( int i = 0; i < newsDbs.size(); ++i )
	    {
	    NewsDb newsDb = (NewsDb) newsDbs.elementAt( i );
	    newsDb.close();
	    }
	newsDbs = null;
	}

    /// Find the sub-database for a given group.
    private NewsDb findNewsDb( String groupName ) throws NewsDbException
	{
	for ( int i = 0; i < groupsPats.size(); ++i )
	    {
	    String groupsPat = (String) groupsPats.elementAt( i );
	    if ( Utils.match( groupsPat, groupName ) )
		return (NewsDb) newsDbs.elementAt( i );
	    }
	throw new NewsDbException( "no database found for group " + groupName );
	}

    }


class MultiplexNewsDbGroups implements Enumeration
    {

    private Enumeration dbEnum;
    private long since;
    private String distsPat;

    private Enumeration groupEnum;
    private NewsDbGroup group;

    public MultiplexNewsDbGroups( Enumeration dbEnum )
	{
	this( dbEnum, -1, null );
	}

    public MultiplexNewsDbGroups( Enumeration dbEnum, long since )
	{
	this( dbEnum, since, null );
	}

    public MultiplexNewsDbGroups( Enumeration dbEnum, long since, String distsPat )
	{
	this.dbEnum = dbEnum;
	this.since = since;
	this.distsPat = distsPat;
	groupEnum = null;
	group = null;
	}

    public boolean hasMoreElements()
	{
	if ( group != null )
	    return true;
	while ( true )
	    {
	    if ( groupEnum == null )
		{
		if ( dbEnum == null )
		    return false;
		if ( ! dbEnum.hasMoreElements() )
		    {
		    dbEnum = null;
		    return false;
		    }
		try
		    {
		    NewsDb db = (NewsDb) dbEnum.nextElement();
		    if ( since != -1 && distsPat != null )
			groupEnum = db.getGroups( since, distsPat );
		    else if ( since != -1 )
			groupEnum = db.getGroups( since );
		    else
			groupEnum = db.getGroups();
		    }
		catch ( NewsDbException e )
		    {
		    continue;
		    }
		}
	    if ( ! groupEnum.hasMoreElements() )
		{
		groupEnum = null;
		continue;
		}
	    group = (NewsDbGroup) groupEnum.nextElement();
	    return true;
	    }
	}
    
    public Object nextElement()
	{
	if ( ! hasMoreElements() )
	    return null;
	NewsDbGroup g = group;
	group = null;
	return g;
	}

    }


class MultiplexNewsDbMessageIds implements Enumeration
    {

    private Enumeration dbEnum;
    private String groupsPat;
    private long since;
    private String distsPat;

    private Enumeration messageIdEnum;
    private String messageId;

    public MultiplexNewsDbMessageIds( Enumeration dbEnum, String groupsPat, long since )
	{
	this( dbEnum, groupsPat, since, null );
	}

    public MultiplexNewsDbMessageIds( Enumeration dbEnum, String groupsPat, long since, String distsPat )
	{
	this.dbEnum = dbEnum;
	this.groupsPat = groupsPat;
	this.since = since;
	this.distsPat = distsPat;
	messageIdEnum = null;
	messageId = null;
	}

    public boolean hasMoreElements()
	{
	if ( messageId != null )
	    return true;
	while ( true )
	    {
	    if ( messageIdEnum == null )
		{
		if ( dbEnum == null )
		    return false;
		if ( ! dbEnum.hasMoreElements() )
		    {
		    dbEnum = null;
		    return false;
		    }
		try
		    {
		    NewsDb db = (NewsDb) dbEnum.nextElement();
		    if ( distsPat != null )
			messageIdEnum = db.getMessageIds( groupsPat, since, distsPat );
		    else
			messageIdEnum = db.getMessageIds( groupsPat, since );
		    }
		catch ( NewsDbException e )
		    {
		    continue;
		    }
		}
	    if ( ! messageIdEnum.hasMoreElements() )
		{
		messageIdEnum = null;
		continue;
		}
	    messageId = (String) messageIdEnum.nextElement();
	    return true;
	    }
	}
    
    public Object nextElement()
	{
	if ( ! hasMoreElements() )
	    return null;
	String mid = messageId;
	messageId = null;
	return mid;
	}

    }