• springIOC原理加载过程


    关于spring ,我以前学过很多次,也看过很多的书.以及博客,但是总是不得要领,这次我再学习一遍,在这里做点记录,如果不对的地方还请大家指正

    Ioc: inverse of controller 控制反转 . 对象的创建权利由程序反转给spring

    什么是IOC容器呢?

      所谓的IOC容器是指的spring bean 工厂里面MAP存储结构(存储了bean的实例)

    spring框架中的工厂有哪些?

      beanFactory 是spring早期创建bean对象工厂接口

      applicationContext()接口实现了beanFactory接口

      实现applicationContext接口的工厂,可以获取到容器中具体bean对象

      实现了beanFactory接口的工厂也可以获取到bean对象

    l ApplicationContext和BeanFactory的区别?

     beanFactory采取的延迟加载,第一次getBean时才会初始化Bean

     applicationContext是加载完applicationContext.xml 就创建了具体的bean实例(只对BeanDefition中描述是单例的bean,才进行恶汉模式创建)

    这里我们看到顶层都是继承与beanfactory 我们常用的就是applicationContext

      applicationContext接口常用实现类

    • classpathXmlApplicationContext : 它是从类的跟路劲下加载配置文件,推荐使用这种
    • FileSystemXmlApplicationContext: 它是从磁盘上加载配置文件,配置文件可以在磁盘的任意位置
    • AnnotationConfigApplicationContext : 当我们使用注解配置容器对象时,需要使用此类来创建 spring 容器。它用来读取注解。

    IOC容器的创建方式

      java创建IOC容器

    ApplicationContext context = new ClassPathXmlApplicationContext(xml路径);

      web 创建IOC 容器:(重点要知道)

    • web服务器(tomcat)启动会加载web.xml(启动ContextLoaderListener监听器):
    • public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
      
          public ContextLoaderListener(WebApplicationContext context) {
              super(context);
          }
      
      
          /**
        serveltContext域对象创建的时候调用这个方法
      * Initialize the root web application context. */ @Override public void contextInitialized(ServletContextEvent event) {
          //初始化web环境中的spring容器 initWebApplicationContext(event.getServletContext()); }
      /** * Close the root web application context. */ @Override public void contextDestroyed(ServletContextEvent event) { closeWebApplicationContext(event.getServletContext()); ContextCleanupListener.cleanupAttributes(event.getServletContext()); } }

      

    当我们点击initWebApplicationContext方法中的时候会发现以下源码

    这个方法在contextLoader之中 也就是Contextloader创建spring容器并初始化spring bean实例

            try {
                // Store context in local instance variable, to guarantee that
                // it is available on ServletContext shutdown.
                if (this.context == null) {
              //这一步就是创建spring容器
    this.context = createWebApplicationContext(servletContext); } if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; if (!cwac.isActive()) { // The context has not yet been refreshed -> provide services such as // setting the parent context, setting the application context id, etc if (cwac.getParent() == null) { // The context instance was injected without an explicit parent -> // determine parent for root web application context, if any. ApplicationContext parent = loadParentContext(servletContext); cwac.setParent(parent); }
    //spring 容器初始化单例bean的实例 configureAndRefreshWebApplicationContext(cwac, servletContext); } }
    configureAndRefreshWebApplicationContext 方法中调用最终初始化Bean的refresh方法
        protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
            if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
                // The application context id is still set to its original default value
                // -> assign a more useful id based on available information
                String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
                if (idParam != null) {
                    wac.setId(idParam);
                }
                else {
                    // Generate default id...
                    wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
                            ObjectUtils.getDisplayString(sc.getContextPath()));
                }
            }
    
            wac.setServletContext(sc);
            String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
            if (configLocationParam != null) {
                wac.setConfigLocation(configLocationParam);
            }
    
            // The wac environment's #initPropertySources will be called in any case when the context
            // is refreshed; do it eagerly here to ensure servlet property sources are in place for
            // use in any post-processing or initialization that occurs below prior to #refresh
            ConfigurableEnvironment env = wac.getEnvironment();
            if (env instanceof ConfigurableWebEnvironment) {
                ((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
            }
    
            customizeContext(sc, wac);
    //不管是web还是java环境都是会调用这个方法实例化bean
            wac.refresh();
        }

    如果web.xml中没有contextClass的元素,那么spring会找到自己的contextLoad.properties文件来加载

    # Default WebApplicationContext implementation class for ContextLoader.
    # Used as fallback when no explicit context implementation has been specified as context-param.
    # Not meant to be customized by application developers.
    
    org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

    IOC容器如何加载bean对象呢?

      跟着上面的refresh()方法我们来到他的源码看看 

      源码来自AbstractApplicationContext

      

    @Override
        public void refresh() throws BeansException, IllegalStateException {
            synchronized (this.startupShutdownMonitor) {
                // Prepare this context for refreshing.
                prepareRefresh();
            //1. 创建真正的bean容器 ConfiurabaleBeanFactroy 

              //2.加载beandefiniton(描述要初始化的Bean的信息)

    
    

                  //3.beandefiniton注册到BeanDefitionRegistry

     
                ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
                // Prepare the bean factory for use in this context.
                prepareBeanFactory(beanFactory);
    
                try {
                    // Allows post-processing of the bean factory in context subclasses.
                    postProcessBeanFactory(beanFactory);

                 //执行实现了BeanFactoryPostProcessor接口的Bean

                      //比如PropertyPlaceHolderConfigurer(context:property-placeholer)就是此处被调用的,替换掉BeanDefition中的占位符(${})中的内容

    // Invoke factory processors registered as beans in the context.
             //针对beandifition实例进行操作
    invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation.
            //主要针对bean实例进行操作的的,
                 //比如容器自动装载了一个AutowiredAnnotationBeanPostProcessor后置处理器(实现@Autowired注解功能) registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons.
          
              //初始化非懒加载方式的单例bean实例 自定的的java类 compent 之类的
              这里的单例可以用过 scope作用域来进行自定义
    finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }

     总结:

      IOC 的原理有几点

      什么是IOC?

      什么是spring容器(IOC容器)?

      如何创建spring容器?(java方式创建和webspring容器的创建方式)

      spring容器如何初始化(就是bean实例 初始化的过程)?

      DI介绍.

      什么是DI 依赖注入

      什么时候进行依赖注入?

      在beandefinition 实例化bean的时候,还未初始化属性 这个时候就调用DI 通过set 或者 构造方式的注入

      @Autowired注解,它是如何生效的?就是在beanpostProcessor对bean处理的时候调用AutowiredBeanPostProcessor类 

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  • 原文地址:https://www.cnblogs.com/bj-xiaodao/p/10777396.html
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