/*
 * Copyright 2002-2019 the original author or authors.
 *
 * 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
 *
 *      https://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,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.context.support;

import java.util.LinkedHashMap;
import java.util.Map;

import javax.servlet.ServletContext;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.config.Scope;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

Scope wrapper for a ServletContext, i.e. for global web application attributes. 
This differs from traditional Spring singletons in that it exposes attributes in the
ServletContext. Those attributes will get destroyed whenever the entire application
shuts down, which might be earlier or later than the shutdown of the containing Spring
ApplicationContext.
The associated destruction mechanism relies on a ContextCleanupListener being registered in web.xml. Note that ContextLoaderListener includes ContextCleanupListener's functionality. 
This scope is registered as default scope with key "application". 
Author:
Juergen Hoeller
See Also:
ContextCleanupListener
Since:
3.0/**
 * {@link Scope} wrapper for a ServletContext, i.e. for global web application attributes.
 *
 * <p>This differs from traditional Spring singletons in that it exposes attributes in the
 * ServletContext. Those attributes will get destroyed whenever the entire application
 * shuts down, which might be earlier or later than the shutdown of the containing Spring
 * ApplicationContext.
 *
 * <p>The associated destruction mechanism relies on a
 * {@link org.springframework.web.context.ContextCleanupListener} being registered in
 * {@code web.xml}. Note that {@link org.springframework.web.context.ContextLoaderListener}
 * includes ContextCleanupListener's functionality.
 *
 * <p>This scope is registered as default scope with key
 * {@link org.springframework.web.context.WebApplicationContext#SCOPE_APPLICATION "application"}.
 *
 * @author Juergen Hoeller
 * @since 3.0
 * @see org.springframework.web.context.ContextCleanupListener
 */
public class ServletContextScope implements Scope, DisposableBean {

	private final ServletContext servletContext;

	private final Map<String, Runnable> destructionCallbacks = new LinkedHashMap<>();


	
Create a new Scope wrapper for the given ServletContext.
Params:
servletContext – the ServletContext to wrap/**
	 * Create a new Scope wrapper for the given ServletContext.
	 * @param servletContext the ServletContext to wrap
	 */
	public ServletContextScope(ServletContext servletContext) {
		Assert.notNull(servletContext, "ServletContext must not be null");
		this.servletContext = servletContext;
	}


	@Override
	public Object get(String name, ObjectFactory<?> objectFactory) {
		Object scopedObject = this.servletContext.getAttribute(name);
		if (scopedObject == null) {
			scopedObject = objectFactory.getObject();
			this.servletContext.setAttribute(name, scopedObject);
		}
		return scopedObject;
	}

	@Override
	@Nullable
	public Object remove(String name) {
		Object scopedObject = this.servletContext.getAttribute(name);
		if (scopedObject != null) {
			synchronized (this.destructionCallbacks) {
				this.destructionCallbacks.remove(name);
			}
			this.servletContext.removeAttribute(name);
			return scopedObject;
		}
		else {
			return null;
		}
	}

	@Override
	public void registerDestructionCallback(String name, Runnable callback) {
		synchronized (this.destructionCallbacks) {
			this.destructionCallbacks.put(name, callback);
		}
	}

	@Override
	@Nullable
	public Object resolveContextualObject(String key) {
		return null;
	}

	@Override
	@Nullable
	public String getConversationId() {
		return null;
	}


	
Invoke all registered destruction callbacks.
To be called on ServletContext shutdown.
See Also:
ContextCleanupListener/**
	 * Invoke all registered destruction callbacks.
	 * To be called on ServletContext shutdown.
	 * @see org.springframework.web.context.ContextCleanupListener
	 */
	@Override
	public void destroy() {
		synchronized (this.destructionCallbacks) {
			for (Runnable runnable : this.destructionCallbacks.values()) {
				runnable.run();
			}
			this.destructionCallbacks.clear();
		}
	}

}