/*
* Copyright (c) 2002-2009 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.kernel.impl.transaction.xaframework;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;
/**
* During recovery (after system crash) the {@link XaLogicalLog} will examine
* the the logical log and re-create any transaction that didn't complete.
* <CODE>XaCommandFactory</CODE> job is to read in commands from the logical
* log and re-create them.
*/
public abstract class XaCommandFactory
{
/**
* Reads the data from a commad previosly written to the logical log and
* creates the command again.
* <p>
* The implementation has to guard against the command beeing corrupt and
* not completly written to the logical log. When unable to read the command
* <CODE>null</CODE> should be returned. <CODE>IOException</CODE> should
* only be thrown in case of real IO failure. The <CODE>null</CODE> return
* is a signal to the recovery mechanism to stop scaning for more entries.
*
* @param fileChannel
* The channel to read the command data from
* @param buffer
* A small buffer that can be used to read data into
* @return The command or null if unable to read command
* @throws IOException
* In case of real IO failure
*/
public abstract XaCommand readCommand( ReadableByteChannel byteChannel,
ByteBuffer buffer ) throws IOException;
}