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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* Licensed under the Apache License, Version 2.0 (the "License");
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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.RegistrySingletonProvider;
import org.jboss.weld.bootstrap.api.helpers.TCCLSingletonProvider;
/**
* A provider of {@link Singleton}s
*
* @see IsolatedStaticSingletonProvider
* @see TCCLSingletonProvider
* @see RegistrySingletonProvider
*
* @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 = RegistrySingletonProvider.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 type of Java object stored in the 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 the explicit 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;
}
}