org.jboss.weld.bootstrap.api.SingletonProvider Maven / Gradle / Ivy
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*
* Copyright 2009 Sun Microsystems, Inc. All rights reserved.
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* Copyright 2010, Red Hat, Inc., and individual contributors
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* full listing of individual contributors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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*/
package org.jboss.weld.bootstrap.api;
import org.jboss.weld.bootstrap.api.helpers.IsolatedStaticSingletonProvider;
import org.jboss.weld.bootstrap.api.helpers.TCCLSingletonProvider;
/**
* A provider of {@link Singleton}s
*
* @see IsolatedStaticSingletonProvider
* @see TCCLSingletonProvider
*
* @author [email protected]
* @author Pete Muir
*/
public abstract class SingletonProvider
{
/*
* Singleton pattern. Upon first access (see instance()), it initializes
* itself by a default implementation. Containers are free to explicitly
* initialize it by calling initialize() method.
*/
private static volatile SingletonProvider INSTANCE;
private static final String DEFAULT_SCOPE_FACTORY = IsolatedStaticSingletonProvider.class.getName();
public static SingletonProvider instance()
{
if (INSTANCE == null)
{
synchronized (SingletonProvider.class)
{
if (INSTANCE == null)
{
/*
* TODO: We should discover ScopeFactory implementation using
* Service Provider Mechanism. In the absence of any explicitly
* configured service, should we default to the default
* implementation.
*/
initializeWithDefaultScope();
}
}
}
return INSTANCE;
}
protected SingletonProvider()
{
}
/**
* Create a new singleton
*
* @param expectedType represents the type of Java object stored in the singleton
* @return a singelton
*/
public abstract Singleton create(Class expectedType);
/**
* Initialize with the default instance
*/
private static void initializeWithDefaultScope()
{
try
{
Class aClass = Class.forName(DEFAULT_SCOPE_FACTORY);
INSTANCE = (SingletonProvider) aClass.newInstance();
}
catch (Exception e)
{
throw new RuntimeException(e);
}
}
/**
* Initialize with an explicit instance
*
* @param instance
*/
public static void initialize(SingletonProvider instance)
{
synchronized (SingletonProvider.class)
{
if (INSTANCE == null)
{
INSTANCE = instance;
}
else
{
throw new RuntimeException("SingletonProvider is already initialized with " + INSTANCE);
}
}
}
public static void reset()
{
INSTANCE = null;
}
}