dxobjectinputstream.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: DxObjectInputStream.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-ObjectInputStream. In
 * gewissen Situationen ist er weniger speicherintensiv. Es koennen
 * allerdings nur Objekte gelesen 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 DxObjectInputStream extends DataInputStream implements ObjectInput {
    protected Hashtable table;
    protected Hashtable classes;
    
    
    public DxObjectInputStream( InputStream in ) {
        super( in );
        table = new Hashtable();
        classes = new Hashtable();
    }
    
    
    public DxObjectInputStream( InputStream in, int bufferSize ) {
        super( new BufferedInputStream( in, bufferSize ) );
        table = new Hashtable();
        classes = new Hashtable();
    }
    
    
    public void reset() {
        table.clear();
        classes.clear();
    //System.out.println ("ObjInputStream.reset()");
    } 
    
    
    public String readClassName() throws IOException {
        String cName = readUTF();
        
        // _R_ und _N_ wird kein Index zugeordnet
        if (cName.equals( ">" ) || cName.equals( "_" )) {
            return cName;
        } 
        
        // klassennamen-referenz aufloesen
        if (cName.equals( "+" )) {
            Integer index = new Integer( readShort() );
            cName = (String)classes.get( index );
        } else {
            classes.put( new Integer( classes.size() ), cName );
        } 
        
        return cName;
    } 
    
    
    public Object readObject() throws IOException {
        try {
            // classenanmen lesen
            String cName = readClassName();
            //System.out.println ("readObject(): className: " + cName);
            Object newObj = null;
            
            if (cName.equals( "_" )) {
                // null - referenz wurde gespeichert
                //System.out.println ("readObject(): null");
                return null;
            } else if (cName.equals( ">" )) {
                // ist Referenz, wurde also schon geladen, entspr. Wert aus table lesen
                Integer hc = new Integer( readInt() );
                newObj = table.get( hc );
                //System.out.println ("readObject(): hashCode ref " + hc + " from " + table.size());
                if (newObj == null) {
                    throw new IOException( "Object not found in referenz table !!" );
                } 
            } else {
                // neues objekt erzeugen
                newObj = Class.forName( cName ).newInstance();
                // hashcode lesen
                Integer hc = new Integer( readInt() );
                //System.out.println ("readObject(): class " + cName + " hashCode " + hc);
                // objekt registrieren
                table.put( hc, newObj );
                // objektdaten lesen
                if (newObj instanceof Externalizable) {
                    ((Externalizable)newObj).readExternal( this );
                } else {
                    throw new IOException( "Object doesn't implement Externalizable" );
                } 
            } 
            return newObj;
        } catch (IOException e) {
            throw e;
        } catch (Exception e) {
            throw new IOException( e.toString() );
        } 
    } 
}