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
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
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. * * <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); }
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