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/*
* Copyright (C) 2022 Archie L. Cobbs. All rights reserved.
*/
package org.dellroad.stuff.spring;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ApplicationObjectSupport;
/**
* Global singleton that provides access to the application context in which it is defined from anywhere.
* Reminiscent of Spring's "evil singleton"
* from days of yore.
*
*
* This bean allows at most one instantiated instance per class loader, and that instance may be defined
* in at most one {@link ApplicationContext}. In particular, this means web containers hosting multiple
* web applications must create separate class loaders per web application.
*
*
* This class may be subclassed to add autowired properties, etc. If so, access the singleton in the same
* way (i.e., via {@link #getInstance Springleton.getInstance()}) and then downcast as needed.
*/
public class Springleton extends ApplicationObjectSupport {
private static Springleton instance;
// Constructor
/**
* Constructor.
*
* @throws IllegalStateException if another instance has already been created in the same class loader
*/
public Springleton() {
synchronized (Springleton.class) {
if (Springleton.instance != null)
throw new IllegalStateException("singleton already instantiated");
Springleton.instance = this;
}
}
// Accessor
/**
* Get the singleton instance.
*
* @return {@link Springleton} singleton
* @throws IllegalStateException if no instance has been created yet
*/
public static Springleton getInstance() {
synchronized (Springleton.class) {
if (Springleton.instance == null)
throw new IllegalStateException("no instance has been created yet");
return Springleton.instance;
}
}
// Methods
/**
* {@inheritDoc}
*
*
* The implementation in {@link Springleton} always returns true.
*/
@Override
public boolean isContextRequired() {
return true;
}
}