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Spring Boot
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/*
 * Copyright 2012-2020 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.boot;

import java.util.function.Supplier;

import org.springframework.context.ApplicationContext;
import org.springframework.core.env.Environment;

/**
 * A simple bootstrap context that is available during startup and {@link Environment}
 * post-processing up to the point that the {@link ApplicationContext} is prepared.
 * 
 * Provides lazy access to singletons that may be expensive to create, or need to be
 * shared before the {@link ApplicationContext} is available.
 *
 * @author Phillip Webb
 * @since 2.4.0
 */
public interface BootstrapContext {

	/**
	 * Return an instance from the context if the type has been registered. The instance
	 * will be created it if it hasn't been accessed previously.
	 * @param  the instance type
	 * @param type the instance type
	 * @return the instance managed by the context
	 * @throws IllegalStateException if the type has not been registered
	 */
	 T get(Class type) throws IllegalStateException;

	/**
	 * Return an instance from the context if the type has been registered. The instance
	 * will be created it if it hasn't been accessed previously.
	 * @param  the instance type
	 * @param type the instance type
	 * @param other the instance to use if the type has not been registered
	 * @return the instance
	 */
	 T getOrElse(Class type, T other);

	/**
	 * Return an instance from the context if the type has been registered. The instance
	 * will be created it if it hasn't been accessed previously.
	 * @param  the instance type
	 * @param type the instance type
	 * @param other a supplier for the instance to use if the type has not been registered
	 * @return the instance
	 */
	 T getOrElseSupply(Class type, Supplier other);

	/**
	 * Return an instance from the context if the type has been registered. The instance
	 * will be created it if it hasn't been accessed previously.
	 * @param  the instance type
	 * @param  the exception to throw if the type is not registered
	 * @param type the instance type
	 * @param exceptionSupplier the supplier which will return the exception to be thrown
	 * @return the instance managed by the context
	 * @throws X if the type has not been registered
	 * @throws IllegalStateException if the type has not been registered
	 */
	 T getOrElseThrow(Class type, Supplier exceptionSupplier) throws X;

	/**
	 * Return if a registration exists for the given type.
	 * @param  the instance type
	 * @param type the instance type
	 * @return {@code true} if the type has already been registered
	 */
	 boolean isRegistered(Class type);

}