本文主要讲解SpringBoot从主方法入口到容器刷新那边的过程，至于容器刷新过程，可以参考之前写的文章：重新学习Spring注解——Spring容器。
一般主方法如下：
@SpringBootApplication public class DemoApplication { public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); } }
跟进主方法，我们来到了类：org.springframework.context.ConfigurableApplicationContext
/** * Static helper that can be used to run a {@link SpringApplication} from the * specified source using default settings. * @param primarySource the primary source to load * @param args the application arguments (usually passed from a Java main method) * @return the running {@link ApplicationContext} */ public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) { return run(new Class<?>[] { primarySource }, args); } // 继续往下走 /** * Static helper that can be used to run a {@link SpringApplication} from the * specified sources using default settings and user supplied arguments. * @param primarySources the primary sources to load * @param args the application arguments (usually passed from a Java main method) * @return the running {@link ApplicationContext} */ public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) { return new SpringApplication(primarySources).run(args); } // 点击run,再往下走 /** * Run the Spring application, creating and refreshing a new * {@link ApplicationContext}. * @param args the application arguments (usually passed from a Java main method) * @return a running {@link ApplicationContext} */ public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>(); configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); Banner printedBanner = printBanner(environment); // 采用策略模式决定创建什么容器：创建ServletWebServer或ReactiveWebServer或主容器 context = createApplicationContext(); exceptionReporters = getSpringFactoriesInstances( SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context); prepareContext(context, environment, listeners, applicationArguments, printedBanner); // 容器刷新 refreshContext(context); afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } listeners.started(context); callRunners(context, applicationArguments); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, listeners); throw new IllegalStateException(ex); } try { listeners.running(context); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, null); throw new IllegalStateException(ex); } return context; } // 接上面：context = createApplicationContext(); /** * Strategy method used to create the {@link ApplicationContext}. By default this * method will respect any explicitly set application context or application context * class before falling back to a suitable default. * @return the application context (not yet refreshed) * @see #setApplicationContextClass(Class) */ protected ConfigurableApplicationContext createApplicationContext() { Class<?> contextClass = this.applicationContextClass; if (contextClass == null) { try { switch (this.webApplicationType) { case SERVLET: contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS); break; case REACTIVE: contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS); break; default: contextClass = Class.forName(DEFAULT_CONTEXT_CLASS); } } catch (ClassNotFoundException ex) { throw new IllegalStateException( "Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass", ex); } } return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass); } // 容器刷新 private void refreshContext(ConfigurableApplicationContext context) { // 关键方法： refresh(context); if (this.registerShutdownHook) { try { context.registerShutdownHook(); } catch (AccessControlException ex) { // Not allowed in some environments. } } } // 接上面关键方法：refresh(context); /** * Refresh the underlying {@link ApplicationContext}. * @param applicationContext the application context to refresh */ protected void refresh(ApplicationContext applicationContext) { Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext); // 容器刷新 ((AbstractApplicationContext) applicationContext).refresh(); }
refresh()真正的方法如下：org.springframework.context.support.AbstractApplicationContext
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. 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); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. 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. 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(); } } }
上面提到的策略模式，会生成三面三种容器中的一种：
/** * The class name of application context that will be used by default for non-web * environments. */ public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context." + "annotation.AnnotationConfigApplicationContext"; /** * The class name of application context that will be used by default for web * environments. */ public static final String DEFAULT_SERVLET_WEB_CONTEXT_CLASS = "org.springframework.boot." + "web.servlet.context.AnnotationConfigServletWebServerApplicationContext"; /** * The class name of application context that will be used by default for reactive web * environments. */ public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework." + "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";
结合下图，核实是否子类（截图虹口），刷新方法一样？
① 针对：org.springframework.context.annotation.AnnotationConfigApplicationContext
public class AnnotationConfigApplicationContext extends GenericApplicationContext implements AnnotationConfigRegistry {} public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry {} // 说明：AnnotationConfigApplicationContext与GenericApplicationContext都没有重写refresh()
② 针对：org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext
public class AnnotationConfigReactiveWebServerApplicationContext extends ReactiveWebServerApplicationContext implements AnnotationConfigRegistry {} public class ReactiveWebServerApplicationContext extends GenericReactiveWebApplicationContext implements ConfigurableWebServerApplicationContext { // 点击super.refresh();跳转org.springframework.context.support.AbstractApplicationContext#refresh @Override public final void refresh() throws BeansException, IllegalStateException { try { super.refresh(); } catch (RuntimeException ex) { stopAndReleaseReactiveWebServer(); throw ex; } } }
③针对：org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext
public class AnnotationConfigServletWebServerApplicationContext extends ServletWebServerApplicationContext implements AnnotationConfigRegistry {} public class ServletWebServerApplicationContext extends GenericWebApplicationContext implements ConfigurableWebServerApplicationContext { // 点击super.refresh();跳转org.springframework.context.support.AbstractApplicationContext#refresh @Override public final void refresh() throws BeansException, IllegalStateException { try { super.refresh(); } catch (RuntimeException ex) { stopAndReleaseWebServer(); throw ex; } } }
所以：容器刷新都是调用 org.springframework.context.support.AbstractApplicationContext#refresh方法。