handleencoder.java

Java Communicating Agents是一个用于开发网络反应式信息agent的框架

/*
 * $Source: /home/data/cvsroot/src/jacomma/icm/io/imp/HandleEncoder.java,v $
 * $Revision: 1.11 $
 * $Date: 2000/10/28 20:09:07 $
 *
 * This file is part of the jacomma framework
 * Copyright (c) 2000 	Dimitrios Vyzovitis
 *			mailto:[e-mail]
 *			
 *
 *			
 *			
 *			
 *
 *	This library is free software; you can redistribute it and/or modify
 *	it under the terms of the GNU Library General Public License as published by
 *	the Free Software Foundation; either version 2 of the License, or
 *	(at your option) any later version.
 *
 *	This library is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *	GNU Library General Public License for more details.
 *
 *	You should have received a copy of the GNU Library General Public License
 *	along with this library; if not, write to the Free Software
 *	Foundation, Inc., 59 Temple Place, Suite 330, 
 *	Boston, MA  02111-1307  USA
 */

package jacomma.icm.io.imp;

import jacomma.icm.io.EncObject;
import jacomma.icm.io.EncObjectType;
import jacomma.icm.io.ObjectEncoder;
import jacomma.icm.io.EncObjectSignature;

import jacomma.icm.type.Handle;
import jacomma.icm.type.Symbol;

import jacomma.util.Cache;

import java.util.ArrayList;

import java.net.InetAddress;

/**
 * TBA
 **/
public class HandleEncoder extends EncoderTemplate {

	ObjectEncoder senc_;
	ObjectEncoder adenc_;
	ObjectEncoder lenc_;
	EncObject esa_;
	
	boolean init_;

	public HandleEncoder() {
		all_.add( Handle.class );
	}
	
	synchronized void _init() {
		// Caching-style Initialization that involves the registry must be moved out 
		// of the constructor - since the latter is called during Registry
		// initialization!!! (thus resluting in race conditions)
		if ( !init_ ) try {
			senc_ = Registry.instance.getEncoder( Symbol.class );
			adenc_ = Registry.instance.getEncoder( InetAddress.class );
			// grab a list encoder that can handle uniform lists
			ArrayList l = new ArrayList();
			l.add( InetAddress.getLocalHost() );
			lenc_ = Registry.instance.getEncoder( l );
			Symbol[] empty = new Symbol[0];
			esa_ = Registry.instance.getEncoder( empty ).encode( empty );
		} catch ( java.net.UnknownHostException exc ) {
			throw new jacomma.util.CheckedException( exc );
		} finally {
			init_ = true;
		}
	}

	public EncObject encode( Object obj, Object hint, boolean s ) {
		_init();
		// hint is ignored
		// elements are not signed - irrespective of s (standard)
		// senc is also passed Symbol type as hint
		// And since the object is not signed at any point before reaching
		// the signer, it is used directly as cache key.
		Handle h = (Handle)obj;
		CacheKey key = new CacheKey( obj );
		EncObject eo = (EncObject)cache_.get( key );
		
		if ( eo == null ) {
			EncObject[] elements = new EncObject[4];
			elements[0] = (h.getTarget() == null) ? 
				esa_ : senc_.encode( h.getTarget(), EncObjectType.Symbol );
			elements[1] = senc_.encode( h.getName(), EncObjectType.Symbol );
			elements[2] = adenc_.encode( h.getHome(), "name" );
			elements[3] = lenc_.encode( h.locations(), adenc_ );
			
			eo = (EncObject)cache_.try_put( key, new EncObjectImp( EncObjectType.Handle, elements ) );
		}

		return s ? sign( eo ) : eo;
	}

}