/*
 * 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
 *
 *      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,
 * 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 javax.servlet.ServletContext;

import org.springframework.beans.factory.FactoryBean;
import org.springframework.lang.Nullable;
import org.springframework.web.context.ServletContextAware;

FactoryBean that fetches a specific, existing ServletContext attribute. Exposes that ServletContext attribute when used as bean reference, effectively making it available as named Spring bean instance. 
Intended to link in ServletContext attributes that exist before
the startup of the Spring application context. Typically, such
attributes will have been put there by third-party web frameworks.
In a purely Spring-based web application, no such linking in of
ServletContext attributes will be necessary.
NOTE: As of Spring 3.0, you may also use the "contextAttributes" default
bean which is of type Map, and dereference it using an "#{contextAttributes.myKey}"
expression to access a specific attribute by name.
Author:
Juergen Hoeller
See Also:
WebApplicationContext.CONTEXT_ATTRIBUTES_BEAN_NAME
ServletContextParameterFactoryBean
Since:
1.1.4/**
 * {@link FactoryBean} that fetches a specific, existing ServletContext attribute.
 * Exposes that ServletContext attribute when used as bean reference,
 * effectively making it available as named Spring bean instance.
 *
 * <p>Intended to link in ServletContext attributes that exist before
 * the startup of the Spring application context. Typically, such
 * attributes will have been put there by third-party web frameworks.
 * In a purely Spring-based web application, no such linking in of
 * ServletContext attributes will be necessary.
 *
 * <p><b>NOTE:</b> As of Spring 3.0, you may also use the "contextAttributes" default
 * bean which is of type Map, and dereference it using an "#{contextAttributes.myKey}"
 * expression to access a specific attribute by name.
 *
 * @author Juergen Hoeller
 * @since 1.1.4
 * @see org.springframework.web.context.WebApplicationContext#CONTEXT_ATTRIBUTES_BEAN_NAME
 * @see ServletContextParameterFactoryBean
 */
public class ServletContextAttributeFactoryBean implements FactoryBean<Object>, ServletContextAware {

	@Nullable
	private String attributeName;

	@Nullable
	private Object attribute;


	
Set the name of the ServletContext attribute to expose.
/**
	 * Set the name of the ServletContext attribute to expose.
	 */
	public void setAttributeName(String attributeName) {
		this.attributeName = attributeName;
	}

	@Override
	public void setServletContext(ServletContext servletContext) {
		if (this.attributeName == null) {
			throw new IllegalArgumentException("Property 'attributeName' is required");
		}
		this.attribute = servletContext.getAttribute(this.attributeName);
		if (this.attribute == null) {
			throw new IllegalStateException("No ServletContext attribute '" + this.attributeName + "' found");
		}
	}


	@Override
	@Nullable
	public Object getObject() throws Exception {
		return this.attribute;
	}

	@Override
	public Class<?> getObjectType() {
		return (this.attribute != null ? this.attribute.getClass() : null);
	}

	@Override
	public boolean isSingleton() {
		return true;
	}

}