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技术文章第一时间送达！
作者：襄垣
juejin.im/post/5c6f730ce51d457f14363a53
推荐阅读(点击即可跳转阅读)
2. 面试题内容聚合
3. 设计模式内容聚合
4. Mybatis内容聚合
5. 多线程内容聚合
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 ApplicationContextConfigurableApplicationContext 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 duplicates Set<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 environment ConfigurableEnvironment 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Bean；
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Context
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
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