什么是Servlet(小服务器)容器/Spring容器

  • 它首先是一个java应用程序，跑在jvm里面
    • 同理还有tomcat jetty etc
    • 他们首先是一个普通的java程序
    • 普通的java程序被人类的指挥精巧地组织起来的成果
    • 可以对他们做一切可以对普通的java程序做的事情
  • 他们遵守java程序的规定(限定)
    • 为什么这里脱离了容器就是null
    • 我想知道这个属性是什么时候被注入的？

web应用是怎么工作的？

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spring容器

核心概念

DI(dependency injection)

IOC(inverse of control)

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对比二者区别

自己手工创建对象，按照依赖关系装配

声明对象的依赖关系，容器自动完成装配

@autowired/@inject

Spring源码导读

1. 容器是怎么启动的以及bean加载

  • BeanFactory（根接口）
    • ApplicationContext（这个就是spring的容器类，实现了上面的那个接口）
  • refresh模板方法
    • 读取bean定义
    • 挨个儿实例化
      • 依赖注入

AbstractApplication类的refresh方法

  1. @Override
  2.     public void refresh() throws BeansException, IllegalStateException {
  3.         synchronized (this.startupShutdownMonitor) {
  4.             StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
  6.             // Prepare this context for refreshing.
  7.             prepareRefresh();
  9.             // Tell the subclass to refresh the internal bean factory.
  10.             ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
  12.             // Prepare the bean factory for use in this context.
  13.             prepareBeanFactory(beanFactory);
  15.             try {
  16.                 // Allows post-processing of the bean factory in context subclasses.
  17.                 postProcessBeanFactory(beanFactory);
  19.                 StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
  20.                 // Invoke factory processors registered as beans in the context.
  21.                 invokeBeanFactoryPostProcessors(beanFactory);
  23.                 // Register bean processors that intercept bean creation.
  24.                 registerBeanPostProcessors(beanFactory);
  25.                 beanPostProcess.end();
  27.                 // Initialize message source for this context.
  28.                 initMessageSource();
  30.                 // Initialize event multicaster for this context.
  31.                 initApplicationEventMulticaster();
  33.                 // Initialize other special beans in specific context subclasses.
  34.                 onRefresh();
  36.                 // Check for listener beans and register them.
  37.                 registerListeners();
  39.                 // Instantiate all remaining (non-lazy-init) singletons.
  40.                 finishBeanFactoryInitialization(beanFactory);
  42.                 // Last step: publish corresponding event.
  43.                 finishRefresh();
  44.             }
  46.             catch (BeansException ex) {
  47.                 if (logger.isWarnEnabled()) {
  48.                     logger.warn("Exception encountered during context initialization - " +
  49.                             "cancelling refresh attempt: " + ex);
  50.                 }
  52.                 // Destroy already created singletons to avoid dangling resources.
  53.                 destroyBeans();
  55.                 // Reset 'active' flag.
  56.                 cancelRefresh(ex);
  58.                 // Propagate exception to caller.
  59.                 throw ex;
  60.             }
  62.             finally {
  63.                 // Reset common introspection caches in Spring's core, since we
  64.                 // might not ever need metadata for singleton beans anymore...
  65.                 resetCommonCaches();
  66.                 contextRefresh.end();
  67.             }
  68.         }
  69.     }
  1. 创建一个applicationContext
  2. 读取所有的bean定义，并且加载
    • 工厂开张了，先招聘了一个主管叫做ConfigurationClassPostProcessor
    • 由这个主管负责找更多的人（扫描更多的bean),
      • 有的主管扫描注解
      • 有的主管读取xml
      • BeanDefinition的资源定位
        • ResourceLoader加载
    • 按照Bean的定义取创建Bean
    • 一些Hook，比如postProcessor

2. 依赖注入

构造器注入

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AbstractAutowiredCapableBeanFactory

ConstructorResolver

Field注入

AutowiredAnnotationBeanPostProcessor负责注入