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

秒速五厘米 2022-12-18 00:57 103阅读 0赞

上次说到Spring有两个核心组件，IOC（控制反转）和AOP（面向切面编程），今天就讲讲什么是Spring的IOC

IOC：Inversion of Control 控制反转  
       一种说法：对象之间的依赖关系，由容器在运行时依据配置文件动态的建立  
       另一种说法：对象的控制器转移了，转到外部容器了，避免了代码的纠缠，代码更容易被维护，模板之间的耦合性降低，容易测试  
    IOC 控制反转意味着将你设计好的类交给容器去控制,而不是在类的内部进行控制,即控制权由应用代码中转到了外部容器

IOC的两种实现方式：  
      DI：Dependency Injection依赖注入,组件不做定位查询,只提供相应方法,由容器创建对象,并调用相应方法设置所需对象需要的组件  
      DL：Dependency Lookup依赖查找,容器创建对象并提供回调接口和上下文环境给组件,需要时通过接口从容器中查找对象  
    依赖查找，现在使用不太多。（EJB使用的更多，将对象创建好后，放到容器中。）  
      
    IOC解决：对象谁来创建的问题——》控制反转  
    DI解决：对象间的关系如何建立的问题。——》依赖注入

org.springframework.beans及org.springframework.context包是IOC容器的基础，就是要使用spring，至少这两个包得存在

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SpringIOC核心API

BeanFactory接口和容器

BeanFactory是Spring中Bean容器,IoC的核心接口,主要用于处理Bean的初始化和配置,建立对象间的依赖关系

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BeanFactory.java 源码：

/*
 * 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.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.
 *
 * 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).
 *
 * 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.
 *
 * 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.
 *
 * 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).
 *
 * 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.
 *
 * 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>
 *
 * 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 created 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.
 	 * 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.
 	 * 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.
 	 * 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)}.
 	 * 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.
 	 * 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.
 	 * 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.
 	 * Allows for specifying explicit constructor arguments / factory method arguments,
 	 * overriding the specified default arguments (if any) in the bean definition.
 	 * 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?
 	 * If the given name is an alias, it will be translated back to the corresponding
 	 * canonical bean name.
 	 * If this factory is hierarchical, will ask any parent factory if the bean cannot
 	 * be found in this factory instance.
 	 * 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?
 	 * 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.
 	 * 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?
 	 * 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.
 	 * 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.
 	 * 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.
 	 * 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.
 	 * For a {@link FactoryBean}, return the type of object that the FactoryBean creates,
 	 * as exposed by {@link FactoryBean#getObjectType()}.
 	 * 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.
 	 * 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.
 	 * 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);
 
 }

定义了如下方法:
 Object getBean(String name) //根据指定名称返回一个Bean实例
 
 <T> T getBean(Class<T> requiredType) //返回一个与给定Class唯一匹配的Bean实例
 
 <T> T getBean(String name, Class<T> requiredType)
 
 Object getBean(String name, Object... args)
 
 Class<?> getType(String name) //得到名称为name的Bean的Class对象
 
 boolean isPrototype(String name) //判断名称为name的Bean是否是原型,即是否总是返回一个新实例
 boolean isSingleton(String name) //判断名称为name的Bean是否是单例
 
 boolean containsBean(String name) //判断是否包含给定名称的Bean实例
 
 boolean isTypeMatch(String name, Class<?> targetType) //判断名称为name的Bean实例是否为targetType类型
 String[] getAliases(String name) //如果名称为name的Bean有别名返回

ApplicationContext接口和容器

该接口继承于BeanFactory,增强了BeanFactory,提供了事务处理AOP,国际化,事件传递

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