dxobjectoutputstream.java

用Java写的面相对象的数据库管理系统

// You can redistribute this software and/or modify it under the terms of
// the Ozone Library License version 1 published by ozone-db.org.
//
// The original code and portions created by SMB are
// Copyright (C) 1997-2000 by SMB GmbH. All rights reserved.
//
// $Id: DxObjectOutputStream.java,v 1.5 2000/10/28 16:55:14 daniela Exp $

package org.ozoneDB.DxLib;

import java.io.*;
import java.util.*;

/**
 * Dieser Stream ist ein Ersatz fuer den Java-ObjectOutputStream. In gewissen
 * Situationen ist er weniger speicherintensiv. Es koennen allerdings nur
 * Objekte geschrieben werden, die das Externalizable-Interface implementieren.
 * 
 * 
 * @author <a href="http://www.softwarebuero.de/">SMB</a>
 * @version $Revision: 1.5 $Date: 2000/10/28 16:55:14 $
 */
public class DxObjectOutputStream extends DataOutputStream implements ObjectOutput {
    protected Hashtable table;
    protected Hashtable classes;
    
    
    public DxObjectOutputStream( OutputStream out ) {
        super( new BufferedOutputStream( out, 4096 ) );
        table = new Hashtable();
        classes = new Hashtable();
    }
    
    
    public DxObjectOutputStream( OutputStream out, int bufferSize ) {
        super( new BufferedOutputStream( out, bufferSize ) );
        table = new Hashtable();
        classes = new Hashtable();
    }
    
    
    public void reset() throws IOException {
        table.clear();
        classes.clear();
        flush();
    //System.out.println ("ObjOutputStream.reset()");
    } 
    
    
    protected void writeClassName( Object obj ) throws IOException {
        String cName = obj.getClass().getName();
        Integer index = (Integer)classes.get( cName );
        if (index == null) {
            //neuer Klassenname
            writeUTF( cName );
            classes.put( cName, new Integer( classes.size() ) );
        } else {
            // Klassenname schon geschrieben
            writeUTF( "+" );
            writeShort( index.intValue() );
        } 
    } 
    
    
    public void writeObject( Object obj ) throws IOException {
        try {
            // falls obj nicht init., wird beim lesen wieder mit null init.
            if (obj == null) {
                writeUTF( "_" );
                //System.out.println ("writeObject(): null ");
                return;
            } 
            
            if (!(obj instanceof Externalizable)) {
                throw new IOException( "Class " + obj.getClass().getName() + " doesn't implement Externalizable" );
            } 
            
            Integer hc = new Integer( System.identityHashCode( obj ) );
            if (!table.containsKey( hc )) {
                // erst registrieren, sonst endlos-rekursion
                table.put( hc, obj );
                // klassennamen speichern
                writeClassName( obj );
                //System.out.println ("writeObject(): hashcode " + hc);
                // hashCode als objID speichern
                writeInt( hc.intValue() );
                // objekt selbst speichern
                ((Externalizable)obj).writeExternal( this );
            } else {
                // obj schon gespeichert
                writeUTF( ">" );
                // hashCode als objID speichern
                writeInt( hc.intValue() );
            //System.out.println ("writeObject(): hashCode ref " + hc);
            } 
        } catch (IOException e) {
            throw e;
        } catch (Exception e) {
            throw new IOException( e.toString() );
        } 
    } 
}