DatabaseMultiplexer.java
/*
** Module : DatabaseMultiplexer.java
** Abstract : Abstract base class which enables multiplexing of service
** requests by physical database
**
** Copyright (c) 2004-2017, Golden Code Development Corporation.
**
** -#- -I- --Date-- -T- --JPRM-- ----------------Description-----------------
** 001 ECF 20071018 ADD @35549 Created initial version. Abstract base class
** which enables multiplexing of service
** requests by physical database.
** 002 ECF 20071128 CHG @36062 Fixed out of bounds condition in workers
** list. Need to seed list with null values at
** initialization.
*/
/*
** This program 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 may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
**
** Additional terms under GNU Affero GPL version 3 section 7:
**
** Under Section 7 of the GNU Affero GPL version 3, the following additional
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** Affero GPL version 3 and may not be removed by you.
**
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**
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*/
package com.goldencode.p2j.persist.remote;
import java.util.*;
import com.goldencode.p2j.persist.*;
import com.goldencode.p2j.util.*;
/**
* The abstract base class of classes which must multiplex work requests to
* multiple worker objects, where each worker is associated with a specific,
* physical database. Upon construction, all databases managed by the current
* P2J server instance are inspected. Client code invokes the {@link
* #getMultiplexID(String)} method to obtain an ID for a particular physical
* database name. This ID will be provided with all future service requests
* and is used to multiplex such requests to the appropriate worker object
* which is associated with that database.
* <p>
* Subclasses are responsible for implementing the actual service methods,
* each of which must accept as a parameter a multiplex ID returned by an
* earlier call to <code>getMultiplexID()</code>. The implementations of
* those methods obtain the appropriate worker object to which the request is
* delegated by invoking {@link #lookupWorker(int)}. This method lazily
* associates a worker object with the database identified by the multiplex
* ID, the first time it is invoked for a particular ID. This is accomplished
* via the {@link #getWorker(Database)} method, which must be implemented by
* the subclass.
* <p>
* Service requests may originate from more than one external server, so this
* implementation is threadsafe.
*
* @param <W>
* Type of worker object being multiplexed.
*
* @author ECF
*/
abstract class DatabaseMultiplexer<W>
implements RemoteMultiplexer<String>
{
/** Databases managed by this P2J server instance */
private final Database[] databases;
/** Worker delegates to which requests will be multiplexed */
private final List<W> workers;
/**
* Default constructor.
*/
protected DatabaseMultiplexer()
{
List<Database> dbs = DatabaseManager.getManagedDatabases();
int size = dbs.size();
databases = dbs.toArray(new Database[size]);
workers = new ArrayList<W>(size);
// Seed workers list with null values; these will be replaced lazily
// as needed.
for (int i = 0; i < size; i++)
{
workers.add(null);
}
}
/**
* Retrieve a unique ID for the given physical database name on this P2J
* server. The ID is guaranteed to be unique within the context of the
* current server instance.
*
* @param key
* Physical database name.
*
* @return ID for the given database which is unique for the server.
*
* @throws IllegalArgumentException
* if no database with the given physical name is configured at
* this server.
*/
public final int getMultiplexID(String key)
{
int len = databases.length;
for (int i = 0; i < len; i++)
{
if (databases[i].getName().equalsIgnoreCase(key))
{
return i;
}
}
throw new IllegalArgumentException("Unrecognized database: " + key);
}
/**
* Access the appropriate worker delegate for the given database ID.
*
* @param id
* Integer which uniquely identifies a physical database being
* managed by the current P2J server instance.
*
* @return Worker associated with the specified database.
*/
protected final W lookupWorker(int id)
{
synchronized (workers)
{
W worker = workers.get(id);
if (worker == null)
{
worker = getWorker(databases[id]);
workers.set(id, worker);
}
return worker;
}
}
/**
* Get the worker object which is associated with the given database.
* The type of this worker and how the association with the database is
* determined by a subclass' particular implementation.
*
* @param database
* Physical database with which the returned worker is associated.
*
* @return Worker object to which service requests associated with the
* given database must be delegated.
*/
protected abstract W getWorker(Database database);
}