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springIOC原理加载过程

作者:互联网

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

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)

  

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(); } } }

 

标签:web,springIOC,容器,spring,wac,bean,context,原理,加载
来源: https://www.cnblogs.com/bj-xiaodao/p/10777396.html