SpringBoot啟動流程分析

從SpringBoot的主類進入SpringApplication的run()方法，然後接着往下分析

1、首先啟動一個StopWatch(秒表)

2、配置awt相關

configureHeadlessProperty();
           

3、從所有的jar包下的META-INF/spring.factories檔案中讀取所有的org.springframework.boot.SpringApplicationRunListener配置的類名通過反射執行個體化并儲存到SpringApplicationRunListeners的listeners(List<SpringApplicationRunListener> listeners)屬性中，并調用SpringApplicationRunListeners的starting方法，既是調用它裡面儲存的所有的SpringApplicationRunListener的starting方法。

SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
           

4、初始化應用參數和環境變量

5、列印Banner

6、建立應用上下文ApplicationContext。根據目前應用的的類型建立不同的應用上下文，如果是web應用則建立AnnotationConfigServletWebServerApplicationContext，如果是REACTIVE反應式web應用則建立AnnotationConfigReactiveWebServerApplicationContext，否則建立基本的AnnotationConfigApplicationContext。

context = createApplicationContext();
           

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);
}
           

7、執行一系列的前置方法prepareContext

prepareContext(context, environment, listeners, applicationArguments, printedBanner);
           

8、屬性應用上下文

refreshContext(context);
           

執行所有的ApplicationContext的父類AbstractApplicationContext的refresh方法，重新整理Spring的IOC容器。

@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();
			}
		}
	}
           

如果目前是web項目，也即是ServletWebServerApplicationContext，則會調用它的onRefresh()方法，然後再調createWebServer方法，建立嵌入式web伺服器，并啟動。

@Override
	protected void onRefresh() {
		super.onRefresh();
		try {
			createWebServer();
		}
		catch (Throwable ex) {
			throw new ApplicationContextException("Unable to start web server", ex);
		}
	}
    

    private void createWebServer() {
		WebServer webServer = this.webServer;
		ServletContext servletContext = getServletContext();
		if (webServer == null && servletContext == null) {
			ServletWebServerFactory factory = getWebServerFactory();
			this.webServer = factory.getWebServer(getSelfInitializer());
		}
		else if (servletContext != null) {
			try {
				getSelfInitializer().onStartup(servletContext);
			}
			catch (ServletException ex) {
				throw new ApplicationContextException("Cannot initialize servlet context", ex);
			}
		}
		initPropertySources();
	}

           

直到最後完全啟動應用。