（2）Spring基础|什么是SpringIOC|简单认识一下Spring IOC

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 * 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
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package org.springframework.beans.factory;
import org.springframework.beans.BeansException;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;
/**
 * The root interface for accessing a Spring bean container.
 * This is the basic client view of a bean container;
 * further interfaces such as {@link ListableBeanFactory} and
 * {@link org.springframework.beans.factory.config.ConfigurableBeanFactory}
 * are available for specific purposes.
 *
 * <p>This interface is implemented by objects that hold a number of bean definitions,
 * each uniquely identified by a String name. Depending on the bean definition,
 * the factory will return either an independent instance of a contained object
 * (the Prototype design pattern), or a single shared instance (a superior
 * alternative to the Singleton design pattern, in which the instance is a
 * singleton in the scope of the factory). Which type of instance will be returned
 * depends on the bean factory configuration: the API is the same. Since Spring
 * 2.0, further scopes are available depending on the concrete application
 * context (e.g. "request" and "session" scopes in a web environment).
 *
 * <p>The point of this approach is that the BeanFactory is a central registry
 * of application components, and centralizes configuration of application
 * components (no more do individual objects need to read properties files,
 * for example). See chapters 4 and 11 of "Expert One-on-One J2EE Design and
 * Development" for a discussion of the benefits of this approach.
 *
 * <p>Note that it is generally better to rely on Dependency Injection
 * ("push" configuration) to configure application objects through setters
 * or constructors, rather than use any form of "pull" configuration like a
 * BeanFactory lookup. Spring's Dependency Injection functionality is
 * implemented using this BeanFactory interface and its subinterfaces.
 *
 * <p>Normally a BeanFactory will load bean definitions stored in a configuration
 * source (such as an XML document), and use the {@code org.springframework.beans}
 * package to configure the beans. However, an implementation could simply return
 * Java objects it creates as necessary directly in Java code. There are no
 * constraints on how the definitions could be stored: LDAP, RDBMS, XML,
 * properties file, etc. Implementations are encouraged to support references
 * amongst beans (Dependency Injection).
 *
 * <p>In contrast to the methods in {@link ListableBeanFactory}, all of the
 * operations in this interface will also check parent factories if this is a
 * {@link HierarchicalBeanFactory}. If a bean is not found in this factory instance,
 * the immediate parent factory will be asked. Beans in this factory instance
 * are supposed to override beans of the same name in any parent factory.
 *
 * <p>Bean factory implementations should support the standard bean lifecycle interfaces
 * as far as possible. The full set of initialization methods and their standard order is:
 * <ol>
 * <li>BeanNameAware's {@code setBeanName}
 * <li>BeanClassLoaderAware's {@code setBeanClassLoader}
 * <li>BeanFactoryAware's {@code setBeanFactory}
 * <li>EnvironmentAware's {@code setEnvironment}
 * <li>EmbeddedValueResolverAware's {@code setEmbeddedValueResolver}
 * <li>ResourceLoaderAware's {@code setResourceLoader}
 * (only applicable when running in an application context)
 * <li>ApplicationEventPublisherAware's {@code setApplicationEventPublisher}
 * (only applicable when running in an application context)
 * <li>MessageSourceAware's {@code setMessageSource}
 * (only applicable when running in an application context)
 * <li>ApplicationContextAware's {@code setApplicationContext}
 * (only applicable when running in an application context)
 * <li>ServletContextAware's {@code setServletContext}
 * (only applicable when running in a web application context)
 * <li>{@code postProcessBeforeInitialization} methods of BeanPostProcessors
 * <li>InitializingBean's {@code afterPropertiesSet}
 * <li>a custom init-method definition
 * <li>{@code postProcessAfterInitialization} methods of BeanPostProcessors
 * </ol>
 *
 * <p>On shutdown of a bean factory, the following lifecycle methods apply:
 * <ol>
 * <li>{@code postProcessBeforeDestruction} methods of DestructionAwareBeanPostProcessors
 * <li>DisposableBean's {@code destroy}
 * <li>a custom destroy-method definition
 * </ol>
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 13 April 2001
 * @see BeanNameAware#setBeanName
 * @see BeanClassLoaderAware#setBeanClassLoader
 * @see BeanFactoryAware#setBeanFactory
 * @see org.springframework.context.ResourceLoaderAware#setResourceLoader
 * @see org.springframework.context.ApplicationEventPublisherAware#setApplicationEventPublisher
 * @see org.springframework.context.MessageSourceAware#setMessageSource
 * @see org.springframework.context.ApplicationContextAware#setApplicationContext
 * @see org.springframework.web.context.ServletContextAware#setServletContext
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization
 * @see InitializingBean#afterPropertiesSet
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization
 * @see DisposableBean#destroy
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getDestroyMethodName
 */
public interface BeanFactory {
  /**
   * Used to dereference a {@link FactoryBean} instance and distinguish it from
   * beans <i>created</i> by the FactoryBean. For example, if the bean named
   * {@code myJndiObject} is a FactoryBean, getting {@code &myJndiObject}
   * will return the factory, not the instance returned by the factory.
   */
  String FACTORY_BEAN_PREFIX = "&";
  /**
   * Return an instance, which may be shared or independent, of the specified bean.
   * <p>This method allows a Spring BeanFactory to be used as a replacement for the
   * Singleton or Prototype design pattern. Callers may retain references to
   * returned objects in the case of Singleton beans.
   * <p>Translates aliases back to the corresponding canonical bean name.
   * Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the name of the bean to retrieve
   * @return an instance of the bean
   * @throws NoSuchBeanDefinitionException if there is no bean with the specified name
   * @throws BeansException if the bean could not be obtained
   */
  Object getBean(String name) throws BeansException;
  /**
   * Return an instance, which may be shared or independent, of the specified bean.
   * <p>Behaves the same as {@link #getBean(String)}, but provides a measure of type
   * safety by throwing a BeanNotOfRequiredTypeException if the bean is not of the
   * required type. This means that ClassCastException can't be thrown on casting
   * the result correctly, as can happen with {@link #getBean(String)}.
   * <p>Translates aliases back to the corresponding canonical bean name.
   * Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the name of the bean to retrieve
   * @param requiredType type the bean must match; can be an interface or superclass
   * @return an instance of the bean
   * @throws NoSuchBeanDefinitionException if there is no such bean definition
   * @throws BeanNotOfRequiredTypeException if the bean is not of the required type
   * @throws BeansException if the bean could not be created
   */
  <T> T getBean(String name, Class<T> requiredType) throws BeansException;
  /**
   * Return an instance, which may be shared or independent, of the specified bean.
   * <p>Allows for specifying explicit constructor arguments / factory method arguments,
   * overriding the specified default arguments (if any) in the bean definition.
   * @param name the name of the bean to retrieve
   * @param args arguments to use when creating a bean instance using explicit arguments
   * (only applied when creating a new instance as opposed to retrieving an existing one)
   * @return an instance of the bean
   * @throws NoSuchBeanDefinitionException if there is no such bean definition
   * @throws BeanDefinitionStoreException if arguments have been given but
   * the affected bean isn't a prototype
   * @throws BeansException if the bean could not be created
   * @since 2.5
   */
  Object getBean(String name, Object... args) throws BeansException;
  /**
   * Return the bean instance that uniquely matches the given object type, if any.
   * <p>This method goes into {@link ListableBeanFactory} by-type lookup territory
   * but may also be translated into a conventional by-name lookup based on the name
   * of the given type. For more extensive retrieval operations across sets of beans,
   * use {@link ListableBeanFactory} and/or {@link BeanFactoryUtils}.
   * @param requiredType type the bean must match; can be an interface or superclass
   * @return an instance of the single bean matching the required type
   * @throws NoSuchBeanDefinitionException if no bean of the given type was found
   * @throws NoUniqueBeanDefinitionException if more than one bean of the given type was found
   * @throws BeansException if the bean could not be created
   * @since 3.0
   * @see ListableBeanFactory
   */
  <T> T getBean(Class<T> requiredType) throws BeansException;
  /**
   * Return an instance, which may be shared or independent, of the specified bean.
   * <p>Allows for specifying explicit constructor arguments / factory method arguments,
   * overriding the specified default arguments (if any) in the bean definition.
   * <p>This method goes into {@link ListableBeanFactory} by-type lookup territory
   * but may also be translated into a conventional by-name lookup based on the name
   * of the given type. For more extensive retrieval operations across sets of beans,
   * use {@link ListableBeanFactory} and/or {@link BeanFactoryUtils}.
   * @param requiredType type the bean must match; can be an interface or superclass
   * @param args arguments to use when creating a bean instance using explicit arguments
   * (only applied when creating a new instance as opposed to retrieving an existing one)
   * @return an instance of the bean
   * @throws NoSuchBeanDefinitionException if there is no such bean definition
   * @throws BeanDefinitionStoreException if arguments have been given but
   * the affected bean isn't a prototype
   * @throws BeansException if the bean could not be created
   * @since 4.1
   */
  <T> T getBean(Class<T> requiredType, Object... args) throws BeansException;
  /**
   * Return a provider for the specified bean, allowing for lazy on-demand retrieval
   * of instances, including availability and uniqueness options.
   * @param requiredType type the bean must match; can be an interface or superclass
   * @return a corresponding provider handle
   * @since 5.1
   * @see #getBeanProvider(ResolvableType)
   */
  <T> ObjectProvider<T> getBeanProvider(Class<T> requiredType);
  /**
   * Return a provider for the specified bean, allowing for lazy on-demand retrieval
   * of instances, including availability and uniqueness options.
   * @param requiredType type the bean must match; can be a generic type declaration.
   * Note that collection types are not supported here, in contrast to reflective
   * injection points. For programmatically retrieving a list of beans matching a
   * specific type, specify the actual bean type as an argument here and subsequently
   * use {@link ObjectProvider#orderedStream()} or its lazy streaming/iteration options.
   * @return a corresponding provider handle
   * @since 5.1
   * @see ObjectProvider#iterator()
   * @see ObjectProvider#stream()
   * @see ObjectProvider#orderedStream()
   */
  <T> ObjectProvider<T> getBeanProvider(ResolvableType requiredType);
  /**
   * Does this bean factory contain a bean definition or externally registered singleton
   * instance with the given name?
   * <p>If the given name is an alias, it will be translated back to the corresponding
   * canonical bean name.
   * <p>If this factory is hierarchical, will ask any parent factory if the bean cannot
   * be found in this factory instance.
   * <p>If a bean definition or singleton instance matching the given name is found,
   * this method will return {@code true} whether the named bean definition is concrete
   * or abstract, lazy or eager, in scope or not. Therefore, note that a {@code true}
   * return value from this method does not necessarily indicate that {@link #getBean}
   * will be able to obtain an instance for the same name.
   * @param name the name of the bean to query
   * @return whether a bean with the given name is present
   */
  boolean containsBean(String name);
  /**
   * Is this bean a shared singleton? That is, will {@link #getBean} always
   * return the same instance?
   * <p>Note: This method returning {@code false} does not clearly indicate
   * independent instances. It indicates non-singleton instances, which may correspond
   * to a scoped bean as well. Use the {@link #isPrototype} operation to explicitly
   * check for independent instances.
   * <p>Translates aliases back to the corresponding canonical bean name.
   * Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the name of the bean to query
   * @return whether this bean corresponds to a singleton instance
   * @throws NoSuchBeanDefinitionException if there is no bean with the given name
   * @see #getBean
   * @see #isPrototype
   */
  boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
  /**
   * Is this bean a prototype? That is, will {@link #getBean} always return
   * independent instances?
   * <p>Note: This method returning {@code false} does not clearly indicate
   * a singleton object. It indicates non-independent instances, which may correspond
   * to a scoped bean as well. Use the {@link #isSingleton} operation to explicitly
   * check for a shared singleton instance.
   * <p>Translates aliases back to the corresponding canonical bean name.
   * Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the name of the bean to query
   * @return whether this bean will always deliver independent instances
   * @throws NoSuchBeanDefinitionException if there is no bean with the given name
   * @since 2.0.3
   * @see #getBean
   * @see #isSingleton
   */
  boolean isPrototype(String name) throws NoSuchBeanDefinitionException;
  /**
   * Check whether the bean with the given name matches the specified type.
   * More specifically, check whether a {@link #getBean} call for the given name
   * would return an object that is assignable to the specified target type.
   * <p>Translates aliases back to the corresponding canonical bean name.
   * Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the name of the bean to query
   * @param typeToMatch the type to match against (as a {@code ResolvableType})
   * @return {@code true} if the bean type matches,
   * {@code false} if it doesn't match or cannot be determined yet
   * @throws NoSuchBeanDefinitionException if there is no bean with the given name
   * @since 4.2
   * @see #getBean
   * @see #getType
   */
  boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException;
  /**
   * Check whether the bean with the given name matches the specified type.
   * More specifically, check whether a {@link #getBean} call for the given name
   * would return an object that is assignable to the specified target type.
   * <p>Translates aliases back to the corresponding canonical bean name.
   * Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the name of the bean to query
   * @param typeToMatch the type to match against (as a {@code Class})
   * @return {@code true} if the bean type matches,
   * {@code false} if it doesn't match or cannot be determined yet
   * @throws NoSuchBeanDefinitionException if there is no bean with the given name
   * @since 2.0.1
   * @see #getBean
   * @see #getType
   */
  boolean isTypeMatch(String name, Class<?> typeToMatch) throws NoSuchBeanDefinitionException;
  /**
   * Determine the type of the bean with the given name. More specifically,
   * determine the type of object that {@link #getBean} would return for the given name.
   * <p>For a {@link FactoryBean}, return the type of object that the FactoryBean creates,
   * as exposed by {@link FactoryBean#getObjectType()}.
   * <p>Translates aliases back to the corresponding canonical bean name.
   * Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the name of the bean to query
   * @return the type of the bean, or {@code null} if not determinable
   * @throws NoSuchBeanDefinitionException if there is no bean with the given name
   * @since 1.1.2
   * @see #getBean
   * @see #isTypeMatch
   */
  @Nullable
  Class<?> getType(String name) throws NoSuchBeanDefinitionException;
  /**
   * Return the aliases for the given bean name, if any.
   * All of those aliases point to the same bean when used in a {@link #getBean} call.
   * <p>If the given name is an alias, the corresponding original bean name
   * and other aliases (if any) will be returned, with the original bean name
   * being the first element in the array.
   * <p>Will ask the parent factory if the bean cannot be found in this factory instance.
   * @param name the bean name to check for aliases
   * @return the aliases, or an empty array if none
   * @see #getBean
   */
  String[] getAliases(String name);
}