coalescerfactory.java

c3p0数据库连接池实现源码

/*
 * Distributed as part of c3p0 v.0.9.1-pre6
 *
 * Copyright (C) 2005 Machinery For Change, Inc.
 *
 * Author: Steve Waldman <[e-mail]>
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License version 2.1, as 
 * published by the Free Software Foundation.
 *
 * This software 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this software; see the file LICENSE.  If not, write to the
 * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 */


package com.mchange.v2.coalesce;

public final class CoalescerFactory
{
    /**
     *  <p>Creates a "Coalescer" that coalesces Objects according to their
     *  equals() method. Given a set of n Objects among whom equals() would
     *  return true, calling coalescer.coalesce() in any order on any sequence 
     *  of these Objects will always return a single "canonical" instance.</p>
     *
     *  <p>This method creates a weak, synchronized coalesecer, safe for use
     *  by multiple Threads.</p>
     */
    public static Coalescer createCoalescer()
    { return createCoalescer( true, true ); }

    /**
     *  <p>Creates a "Coalescer" that coalesces Objects according to their
     *  equals() method. Given a set of n Objects among whom equals() would
     *  return true, calling coalescer.coalesce() in any order on any sequence 
     *  of these Objects will always return a single "canonical" instance.</p>
     *
     *  @param weak if true, the Coalescer will use WeakReferences to hold
     *              its canonical instances, allowing them to be garbage
     *              collected if they are nowhere in use.
     *
     *  @param synced if true, access to the Coalescer will be automatically
     *                synchronized. if set to false, then users must manually
     *                synchronize access.
     */
    public static Coalescer createCoalescer( boolean weak, boolean synced )
    { return createCoalescer( null, weak, synced ); }

    /**
     *  <p>Creates a "Coalescer" that coalesces Objects according to the
     *  checkCoalesce() method of a "CoalesceChecker". Given a set of 
     *  n Objects among whom calling cc.checkCoalesce() on any pair would
     *  return true, calling coalescer.coalesce() in any order on any sequence 
     *  of these Objects will always return a single "canonical" instance.
     *  This allows one to define immutable value Objects whose equals() 
     *  method is a mere identity test -- one can use a Coalescer in a 
     *  factory method to ensure that no two instances with the same values
     *  are made available to clients.</p>
     *
     * @param cc CoalesceChecker that will be used to determine whether two
     *           objects are equivalent and can be coalesced. [If cc is null, then two
     *           objects will be coalesced iff o1.equals( o2 ).]
     *
     *  @param weak if true, the Coalescer will use WeakReferences to hold
     *              its canonical instances, allowing them to be garbage
     *              collected if they are nowhere in use.
     *
     *  @param synced if true, access to the Coalescer will be automatically
     *                synchronized. if set to false, then users must manually
     *                synchronize access.
     */
    public static Coalescer createCoalescer( CoalesceChecker cc, boolean weak, boolean synced )
    {
	Coalescer out;
	if ( cc == null )
	    {
		out = ( weak ? 
			(Coalescer) new WeakEqualsCoalescer() : 
			(Coalescer) new StrongEqualsCoalescer() );
	    }
	else
	    {
		out = ( weak ? 
			(Coalescer) new WeakCcCoalescer( cc ) : 
			(Coalescer) new StrongCcCoalescer( cc ) );
	    }
	return ( synced ? new SyncedCoalescer( out ) : out );
    }

}