spring boot 启动

springboot启动流程主要分为三个部分：第一部分进行SpringApplication的初始化模块，配置一些基本的环境变量、资源、构造器、监听器，第二部分实现了应用具体的启动方案，包括启动流程的监听模块、加载配置环境模块、及核心的创建上下文环境模块，第三部分是自动化配置模块，该模块作为springboot自动配置核心，在后面的分析中会详细讨论。在下面的启动程序中我们会串联起结构中的主要功能。

轮回教主

4621人浏览 · 2022-05-17 21:08:00

轮回教主 · 2022-05-17 21:08:00 发布

springboot启动流程主要分为三个部分：

第一部分进行SpringApplication的初始化模块，配置一些基本的环境变量、资源、构造器、监听器，

第二部分实现了应用具体的启动方案，包括启动流程的监听模块、加载配置环境模块、及核心的创建上下文环境模块，

第三部分是自动化配置模块，该模块作为springboot自动配置核心，在后面的分析中会详细讨论。在下面的启动程序中我们会串联起结构中的主要功能。

每个SpringBoot程序都有一个主入口，也就是main方法，main里面调用SpringApplication.run()启动整个spring-boot程序，该方法所在类需要使用@SpringBootApplication注解，以及@ImportResource注解(if need)，

@SpringBootApplication包括三个注解，功能如下：

@EnableAutoConfiguration：SpringBoot根据应用所声明的依赖来对Spring框架进行自动配置

@SpringBootConfiguration(内部为@Configuration)：被标注的类等于在spring的XML配置文件中(applicationContext.xml)，装配所有bean事务，提供了一个spring的上下文环境

@ComponentScan：组件扫描，可自动发现和装配Bean，默认扫描SpringApplication的run方法里的Booter.class所在的包路径下文件，所以最好将该启动类放到根包路径下

下面详细介绍各个启动的环节：

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1、创建并启动计时监控类，可以看到记录当前任务的名称，默认是空字符串，然后记录当前springboot应用启动的开始时间。

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StopWatch stopWatch = new StopWatch();

stopWatch.start();

//详细源代码

public void start() throws IllegalStateException {

start("");

}

public void start(String taskName) throws IllegalStateException {

if (this.currentTaskName != null) {

throw new IllegalStateException("Can't start StopWatch: it's already running");

}

this.currentTaskName = taskName;

this.startTimeNanos = System.nanoTime();

}

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2、初始化应用上下文和异常报告集合

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ConfigurableApplicationContext context = null;

Collection

exceptionReporters = new ArrayList<>();

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3、设置系统属性java.awt.headless的值：

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java.awt.headless模式是在缺少显示屏、键盘或者鼠标的系统配置

当配置了如下属性之后，应用程序可以执行如下操作：

1、创建轻量级组件

2、收集关于可用的字体、字体指标和字体设置的信息

3、设置颜色来渲染准备图片

4、创造和获取图像，为渲染准备图片

5、使用java.awt.PrintJob,java.awt.print.*和javax.print.*类里的方法进行打印

private void configureHeadlessProperty() {

System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS,

System.getProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));

}

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4、创建所有spring运行监听器并发布应用启动事件

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SpringApplicationRunListeners listeners = getRunListeners(args);

listeners.starting();

//创建spring监听器

private SpringApplicationRunListeners getRunListeners(String[] args) {

Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };

return new SpringApplicationRunListeners(logger,

getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));

}

SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) {

this.log = log;

this.listeners = new ArrayList<>(listeners);

}

//循环遍历获取监听器

void starting() {

for (SpringApplicationRunListener listener : this.listeners) {

listener.starting();

}

//此处的监听器可以看出是事件发布监听器，主要用来发布启动事件

@Override

public void starting() {

//这里是创建application事件‘applicationStartingEvent’

this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));

}

//applicationStartingEvent是springboot框架最早执行的监听器，在该监听器执行started方法时，会继续发布事件，主要是基于spring的事件机制

@Override

public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {

ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));

//获取线程池，如果为空则同步处理。这里线程池为空，还未初始化

Executor executor = getTaskExecutor();

for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {

if (executor != null) {

//异步发送事件

executor.execute(() -> invokeListener(listener, event));

}

else {

//同步发送事件

invokeListener(listener, event);

}

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5、初始化默认应用参数类

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ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);

public DefaultApplicationArguments(String... args) {

Assert.notNull(args, "Args must not be null");

this.source = new Source(args);

this.args = args;

}

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6、根据运行监听器和应用参数来准备spring环境

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ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);

//详细环境的准备

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,

ApplicationArguments applicationArguments) {

// 获取或者创建应用环境

ConfigurableEnvironment environment = getOrCreateEnvironment();

// 配置应用环境，配置propertySource和activeProfiles

configureEnvironment(environment, applicationArguments.getSourceArgs());

//listeners环境准备，广播ApplicationEnvironmentPreparedEvent

ConfigurationPropertySources.attach(environment);

listeners.environmentPrepared(environment);

//将环境绑定给当前应用程序

bindToSpringApplication(environment);

//对当前的环境类型进行判断，如果不一致进行转换

if (!this.isCustomEnvironment) {

environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,

deduceEnvironmentClass());

}

//配置propertySource对它自己的递归依赖

ConfigurationPropertySources.attach(environment);

return environment;

}

// 获取或者创建应用环境，根据应用程序的类型可以分为servlet环境、标准环境(特殊的非web环境)和响应式环境

private ConfigurableEnvironment getOrCreateEnvironment() {

//存在则直接返回

if (this.environment != null) {

return this.environment;

}

//根据webApplicationType创建对应的Environment

switch (this.webApplicationType) {

case SERVLET:

return new StandardServletEnvironment();

case REACTIVE:

return new StandardReactiveWebEnvironment();

default:

return new StandardEnvironment();

}

//配置应用环境

protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {

if (this.addConversionService) {

ConversionService conversionService = ApplicationConversionService.getSharedInstance();

environment.setConversionService((ConfigurableConversionService) conversionService);

}

//配置property sources

configurePropertySources(environment, args);

//配置profiles

configureProfiles(environment, args);

}

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7、创建banner的打印类

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Banner printedBanner = printBanner(environment);//打印类的详细操作过程private Banner printBanner(ConfigurableEnvironment environment) { if (this.bannerMode == Banner.Mode.OFF) { return null; } ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader : new DefaultResourceLoader(getClassLoader()); SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner); if (this.bannerMode == Mode.LOG) { return bannerPrinter.print(environment, this.mainApplicationClass, logger); } return bannerPrinter.print(environment, this.mainApplicationClass, System.out); }

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8、创建应用的上下文:根据不同哦那个的应用类型初始化不同的上下文应用类

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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); }

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9、准备异常报告器

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exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context);private

Collection

getSpringFactoriesInstances(Class

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10、准备应用上下文

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prepareContext(context, environment, listeners, applicationArguments, printedBanner);private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) { //应用上下文的environment context.setEnvironment(environment); //应用上下文后处理 postProcessApplicationContext(context); //为上下文应用所有初始化器，执行容器中的applicationContextInitializer(spring.factories的实例)，将所有的初始化对象放置到context对象中 applyInitializers(context); //触发所有SpringApplicationRunListener监听器的ContextPrepared事件方法。添加所有的事件监听器 listeners.contextPrepared(context); //记录启动日志 if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); } // 注册启动参数bean，将容器指定的参数封装成bean，注入容器 ConfigurableListableBeanFactory beanFactory = context.getBeanFactory(); beanFactory.registerSingleton("springApplicationArguments", applicationArguments); //设置banner if (printedBanner != null) { beanFactory.registerSingleton("springBootBanner", printedBanner); } if (beanFactory instanceof DefaultListableBeanFactory) { ((DefaultListableBeanFactory) beanFactory) .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding); } if (this.lazyInitialization) { context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor()); } // 加载所有资源，指的是启动器指定的参数 Set

sources = getAllSources(); Assert.notEmpty(sources, "Sources must not be empty"); //将bean加载到上下文中 load(context, sources.toArray(new Object[0])); //触发所有springapplicationRunListener监听器的contextLoaded事件方法， listeners.contextLoaded(context); }------------------- //这里没有做任何的处理过程，因为beanNameGenerator和resourceLoader默认为空，可以方便后续做扩展处理 protected void postProcessApplicationContext(ConfigurableApplicationContext context) { if (this.beanNameGenerator != null) { context.getBeanFactory().registerSingleton(AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, this.beanNameGenerator); } if (this.resourceLoader != null) { if (context instanceof GenericApplicationContext) { ((GenericApplicationContext) context).setResourceLoader(this.resourceLoader); } if (context instanceof DefaultResourceLoader) { ((DefaultResourceLoader) context).setClassLoader(this.resourceLoader.getClassLoader()); } } if (this.addConversionService) { context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance()); } }--------------------- //将启动器类加载到spring容器中，为后续的自动化配置奠定基础，之前看到的很多注解也与此相关 protected void load(ApplicationContext context, Object[] sources) { if (logger.isDebugEnabled()) { logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources)); } BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources); if (this.beanNameGenerator != null) { loader.setBeanNameGenerator(this.beanNameGenerator); } if (this.resourceLoader != null) { loader.setResourceLoader(this.resourceLoader); } if (this.environment != null) { loader.setEnvironment(this.environment); } loader.load(); }--------------------- //springboot会优先选择groovy加载方式，找不到在选择java方式 private int load(Class<?> source) { if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) { // Any GroovyLoaders added in beans{} DSL can contribute beans here GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class); load(loader); } if (isComponent(source)) { this.annotatedReader.register(source); return 1; } return 0; }

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11、刷新应用上下文

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refreshContext(context);private void refreshContext(ConfigurableApplicationContext context) { refresh(context); if (this.registerShutdownHook) { try { context.registerShutdownHook(); } catch (AccessControlException ex) { // Not allowed in some environments. } } }------------ public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. //刷新上下文环境，初始化上下文环境，对系统的环境变量或者系统属性进行准备和校验 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. //初始化beanfactory，解析xml，相当于之前的xmlBeanfactory操作 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. //为上下文准备beanfactory，对beanFactory的各种功能进行填充，如@autowired，设置spel表达式解析器，设置编辑注册器，添加applicationContextAwareprocessor处理器等等 prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. //提供子类覆盖的额外处理，即子类处理自定义的beanfactorypostProcess postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. //激活各种beanfactory处理器 invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. //注册拦截bean创建的bean处理器，即注册beanPostProcessor registerBeanPostProcessors(beanFactory); // Initialize message source for this context. //初始化上下文中的资源文件如国际化文件的处理 initMessageSource(); // Initialize event multicaster for this context. //初始化上下文事件广播器 initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. //给子类扩展初始化其他bean onRefresh(); // Check for listener beans and register them. //在所有的bean中查找listener bean,然后注册到广播器中 registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. //初始化剩余的非懒惰的bean，即初始化非延迟加载的bean finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. //发完成刷新过程，通知声明周期处理器刷新过程，同时发出ContextRefreshEvent通知别人 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(); } } }

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12、应用上下文刷新后置处理

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afterRefresh(context, applicationArguments);//当前方法的代码是空的，可以做一些自定义的后置处理操作protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) { }

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13、停止计时监控类：计时监听器停止，并统计一些任务执行信息

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stopWatch.stop();public void stop() throws IllegalStateException { if (this.currentTaskName == null) { throw new IllegalStateException("Can't stop StopWatch: it's not running"); } long lastTime = System.nanoTime() - this.startTimeNanos; this.totalTimeNanos += lastTime; this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime); if (this.keepTaskList) { this.taskList.add(this.lastTaskInfo); } ++this.taskCount; this.currentTaskName = null; }

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14、输出日志记录执行主类名、时间信息

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if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);}

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15、发布应用上下文启动完成事件：触发所有SpringapplicationRunListener监听器的started事件方法

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listeners.started(context); void started(ConfigurableApplicationContext context) { for (SpringApplicationRunListener listener : this.listeners) { listener.started(context); } }

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16、执行所有Runner执行器：执行所有applicationRunner和CommandLineRunner两种运行器

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callRunners(context, applicationArguments);private void callRunners(ApplicationContext context, ApplicationArguments args) { List

runners = new ArrayList<>(); runners.addAll(context.getBeansOfType(ApplicationRunner.class).values()); runners.addAll(context.getBeansOfType(CommandLineRunner.class).values()); AnnotationAwareOrderComparator.sort(runners); for (Object runner : new LinkedHashSet<>(runners)) { if (runner instanceof ApplicationRunner) { callRunner((ApplicationRunner) runner, args); } if (runner instanceof CommandLineRunner) { callRunner((CommandLineRunner) runner, args); } } }

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17、发布应用上下文就绪事件：触发所有springapplicationRunnListener将挺起的running事件方法

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listeners.running(context);void running(ConfigurableApplicationContext context) { for (SpringApplicationRunListener listener : this.listeners) { listener.running(context); } }

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18、返回应用上下文

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return context;