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前言

springboot2.5.6版本

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入口

public static void main(String[] args) {SpringApplication.run(KafkaMain.class, args);
}

一、SpringApplication构造器

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {this.resourceLoader = resourceLoader;Assert.notNull(primarySources, "PrimarySources must not be null");this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));//1.获取应用类型this.webApplicationType = WebApplicationType.deduceFromClasspath();//2.加载META-INF/spring.factories下所有的 BootstrapRegistryInitializerthis.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();//3.加载META-INF/spring.factories下所有的 ApplicationContextInitializer 初始化器setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));//4.加载META-INF/spring.factories 下所有的 ApplicationListener 监听器setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));//5.检查启动类this.mainApplicationClass = deduceMainApplicationClass();
}

我需要了解spring内置注入的这些类是做什么的：
BootstrapRegistryInitializer

ApplicationContextInitializer
添加的初始化器

ApplicationListener
添加的监听器

二 run

//运行 Spring 应用程序，创建并刷新一个新的ApplicationContext 
public ConfigurableApplicationContext run(String... args) {//记录程序运行时间StopWatch stopWatch = new StopWatch();stopWatch.start();DefaultBootstrapContext bootstrapContext = createBootstrapContext();//ConfigurableApplicationContext Spring 的上下文ConfigurableApplicationContext context = null;configureHeadlessProperty();//加载META-INF/spring.factories下所有的 SpringApplicationRunListeneSpringApplicationRunListeners listeners = getRunListeners(args);//发布应用启动事件 触发LoggingApplicationListener监听器listeners.starting(bootstrapContext, this.mainApplicationClass);try {//存储argsApplicationArguments applicationArguments = new DefaultApplicationArguments(args);//准备环境ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);context = createApplicationContext();context.setApplicationStartup(this.applicationStartup);prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);//刷新容器refreshContext(context);afterRefresh(context, applicationArguments);stopWatch.stop();if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);}listeners.started(context);//容器刷新完成 回调ApplicationRunner  CommandLineRunnercallRunners(context, applicationArguments);} catch (Throwable ex) {handleRunFailure(context, ex, listeners);throw new IllegalStateException(ex);}try {listeners.running(context);} catch (Throwable ex) {handleRunFailure(context, ex, null);throw new IllegalStateException(ex);}return context;
}

三 prepareEnvironment（）

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {// 获取或者创建 environment。这里获取类型是 StandardServletEnvironmentConfigurableEnvironment environment = getOrCreateEnvironment();// 将入参配置到环境配置中configureEnvironment(environment, applicationArguments.getSourceArgs());ConfigurationPropertySources.attach(environment);//发布环境准备时间ApplicationEnvironmentPreparedEvent, 触发EnvironmentPostProcessorApplicationListener监听器listeners.environmentPrepared(bootstrapContext, environment);DefaultPropertiesPropertySource.moveToEnd(environment);Assert.state(!environment.containsProperty("spring.main.environment-prefix"),"Environment prefix cannot be set via properties.");bindToSpringApplication(environment);if (!this.isCustomEnvironment) {environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,deduceEnvironmentClass());}ConfigurationPropertySources.attach(environment);return environment;
}

四 prepareContext（）

private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments, Banner printedBanner) {//设置环境context.setEnvironment(environment);postProcessApplicationContext(context);//应用 SpringApplication 构造器中加载的ApplicationContextInitializerapplyInitializers(context);//发布 容器 初始化完成事件ApplicationContextInitializedEvent,bean定义被加载之前listeners.contextPrepared(context);bootstrapContext.close(context);if (this.logStartupInfo) {logStartupInfo(context.getParent() == null);logStartupProfileInfo(context);}// Add boot specific singleton beansConfigurableListableBeanFactory beanFactory = context.getBeanFactory();beanFactory.registerSingleton("springApplicationArguments", applicationArguments);if (printedBanner != null) {beanFactory.registerSingleton("springBootBanner", printedBanner);}if (beanFactory instanceof DefaultListableBeanFactory) {((DefaultListableBeanFactory) beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);}if (this.lazyInitialization) {context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());}// Load the sourcesSet<Object> sources = getAllSources();Assert.notEmpty(sources, "Sources must not be empty");// 这里将启动类加入到 beanDefinitionMap 中，为后续的自动化配置做好了基础load(context, sources.toArray(new Object[0]));//发布应用准备事件ApplicationPreparedEventlisteners.contextLoaded(context);
}