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.将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