SpringBoot是如何动起来的

程序入口

SpringApplication.run(BeautyApplication.class, args);

执行此方法来加载整个SpringBoot的环境。

1.从哪儿开始？

SpringApplication.java

    /*** 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) {//...}

调用SpringApplication.java中的run方法，目的是加载Spring Application，同时返回ApplicationContext。

2.执行了什么？

2.1计时

记录整个Spring Application的加载时间！

StopWatch stopWatch = new StopWatch();
stopWatch.start();
// ...
stopWatch.stop();
if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}

2.2声明

// 声明 ApplicationContext
ConfigurableApplicationContext context = null;
// 声明 一个异常报告集合
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();

2.3指定程序运行模式

指定java.awt.headless，默认是true

一般是在程序开始激活headless模式，告诉程序，现在你要工作在Headless mode下，就不要指望硬件帮忙了，你得自力更生，依靠系统的计算能力模拟出这些特性来。

private void configureHeadlessProperty() {System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, System.getProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
}

2.4配置监听并发布应用启动事件

SpringApplicationRunListener负责加载ApplicationListener事件。

SpringApplicationRunListeners listeners = getRunListeners(args);
// 开始
listeners.starting();
// 处理所有 property sources 配置和 profiles 配置，准备环境，分为标准 Servlet 环境和标准环境
ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
// 准备应用上下文
prepareContext(context, environment, listeners, applicationArguments,printedBanner);
// 完成
listeners.started(context);
// 异常
handleRunFailure(context, ex, exceptionReporters, listeners);
// 执行
listeners.running(context);

getRunListeners中根据type = SpringApplicationRunListener.class去拿到了所有的Listener并根据优先级排序。

对应的就是META-INF / spring.factories文件中的org.springframework.boot.SpringApplicationRunListener = org.springframework.boot.context.event.EventPublishingRunListener

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,Class<?>[] parameterTypes, Object... args) {ClassLoader classLoader = Thread.currentThread().getContextClassLoader();// Use names and ensure unique to protect against duplicatesSet<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));List<T> instances = createSpringFactoriesInstances(type, parameterTypes,classLoader, args, names);AnnotationAwareOrderComparator.sort(instances);return instances;}

在ApplicationListener中，可以针对任何一个阶段插入处理代码。

public interface SpringApplicationRunListener {/*** Called immediately when the run method has first started. Can be used for very* early initialization.*/void starting();/*** Called once the environment has been prepared, but before the* {@link ApplicationContext} has been created.* @param environment the environment*/void environmentPrepared(ConfigurableEnvironment environment);/*** Called once the {@link ApplicationContext} has been created and prepared, but* before sources have been loaded.* @param context the application context*/void contextPrepared(ConfigurableApplicationContext context);/*** Called once the application context has been loaded but before it has been* refreshed.* @param context the application context*/void contextLoaded(ConfigurableApplicationContext context);/*** The context has been refreshed and the application has started but* {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner* ApplicationRunners} have not been called.* @param context the application context.* @since 2.0.0*/void started(ConfigurableApplicationContext context);/*** Called immediately before the run method finishes, when the application context has* been refreshed and all {@link CommandLineRunner CommandLineRunners} and* {@link ApplicationRunner ApplicationRunners} have been called.* @param context the application context.* @since 2.0.0*/void running(ConfigurableApplicationContext context);/*** Called when a failure occurs when running the application.* @param context the application context or {@code null} if a failure occurred before* the context was created* @param exception the failure* @since 2.0.0*/void failed(ConfigurableApplicationContext context, Throwable exception);}

3.每个阶段执行的内容

3.1 listeners.starting（）;

在加载Spring Application之前执行，所有资源和环境未被加载。

3.2 prepareEnvironment（listeners，applicationArguments）;

创建ConfigurableEnvironment;

将配置的环境绑定到Spring Application中;

    private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) {// Create and configure the environmentConfigurableEnvironment environment = getOrCreateEnvironment();configureEnvironment(environment, applicationArguments.getSourceArgs());listeners.environmentPrepared(environment);bindToSpringApplication(environment);if (this.webApplicationType == WebApplicationType.NONE) {environment = new EnvironmentConverter(getClassLoader()).convertToStandardEnvironmentIfNecessary(environment);}ConfigurationPropertySources.attach(environment);return environment;}

3.3 prepareContext

配置忽略的豆;

    private void configureIgnoreBeanInfo(ConfigurableEnvironment environment) {if (System.getProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME) == null) {Boolean ignore = environment.getProperty("spring.beaninfo.ignore",Boolean.class, Boolean.TRUE);System.setProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME,ignore.toString());}}

打印日志 - 加载的资源

Banner printedBanner = printBanner(environment);

根据不同的WebApplicationType创建上下文

context = createApplicationContext();

3.4 refreshContext

支持定制刷新

    /*** Register a shutdown hook with the JVM runtime, closing this context* on JVM shutdown unless it has already been closed at that time.* <p>This method can be called multiple times. Only one shutdown hook* (at max) will be registered for each context instance.* @see java.lang.Runtime#addShutdownHook* @see #close()*/void registerShutdownHook();

3.5 afterRefresh

刷新后的实现方法暂未实现

    /*** Called after the context has been refreshed.* @param context the application context* @param args the application arguments*/protected void afterRefresh(ConfigurableApplicationContext context,ApplicationArguments args) {}

3.6 listeners.started（context）;

到此为止，Spring Application的环境和资源都加载完毕了;

发布应用上下文启动完成事件;

执行所有Runner运行器 - 执行所有ApplicationRunner和CommandLineRunner这两种运行器

// 启动
callRunners(context, applicationArguments);

3.7 listeners.running（context）;

触发所有SpringApplicationRunListener监听器的running事件方法