/*
 * Copyright 2002-2017 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.request;

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

Abstract Scope implementation that reads from a particular scope in the current thread-bound RequestAttributes object. 
Subclasses simply need to implement getScope() to instruct this class which RequestAttributes scope to read attributes from. 
Subclasses may wish to override the get and remove methods to add synchronization around the call back into this super class. 
Author:
Rod Johnson, Juergen Hoeller, Rob Harrop
Since:
2.0/**
 * Abstract {@link Scope} implementation that reads from a particular scope
 * in the current thread-bound {@link RequestAttributes} object.
 *
 * <p>Subclasses simply need to implement {@link #getScope()} to instruct
 * this class which {@link RequestAttributes} scope to read attributes from.
 *
 * <p>Subclasses may wish to override the {@link #get} and {@link #remove}
 * methods to add synchronization around the call back into this super class.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 2.0
 */
public abstract class AbstractRequestAttributesScope implements Scope {

	@Override
	public Object get(String name, ObjectFactory<?> objectFactory) {
		RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
		Object scopedObject = attributes.getAttribute(name, getScope());
		if (scopedObject == null) {
			scopedObject = objectFactory.getObject();
			attributes.setAttribute(name, scopedObject, getScope());
			// Retrieve object again, registering it for implicit session attribute updates.
			// As a bonus, we also allow for potential decoration at the getAttribute level.
			Object retrievedObject = attributes.getAttribute(name, getScope());
			if (retrievedObject != null) {
				// Only proceed with retrieved object if still present (the expected case).
				// If it disappeared concurrently, we return our locally created instance.
				scopedObject = retrievedObject;
			}
		}
		return scopedObject;
	}

	@Override
	@Nullable
	public Object remove(String name) {
		RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
		Object scopedObject = attributes.getAttribute(name, getScope());
		if (scopedObject != null) {
			attributes.removeAttribute(name, getScope());
			return scopedObject;
		}
		else {
			return null;
		}
	}

	@Override
	public void registerDestructionCallback(String name, Runnable callback) {
		RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
		attributes.registerDestructionCallback(name, callback, getScope());
	}

	@Override
	@Nullable
	public Object resolveContextualObject(String key) {
		RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
		return attributes.resolveReference(key);
	}


	
Template method that determines the actual target scope.
See Also:
RequestAttributes.SCOPE_REQUEST
RequestAttributes.SCOPE_SESSION
Returns:
the target scope, in the form of an appropriate RequestAttributes constant/**
	 * Template method that determines the actual target scope.
	 * @return the target scope, in the form of an appropriate
	 * {@link RequestAttributes} constant
	 * @see RequestAttributes#SCOPE_REQUEST
	 * @see RequestAttributes#SCOPE_SESSION
	 */
	protected abstract int getScope();

}