SpringBoot是如何動起來的

程序入口

SpringApplication.run(BeautyApplication.class, args);
複製代碼

執行此方法來加載整個SpringBoot的環境。

1. 從哪兒開始？

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) {
		//...
  }
複製代碼

調用SpringApplication.java 中的 run 方法，目的是加載Spring Application，同時返回 ApplicationContext。

2. 執行了什麼？

2.1 計時

記錄整個Spring Application的加載時間！

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

2.2 聲明

// 聲明 ApplicationContext
ConfigurableApplicationContext context = null;
// 聲明 一個異常報告集合
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
複製代碼

2.3 指定程序運行模式

指定 java.awt.headless，默認是true 通常是在程序開始激活headless模式，告訴程序，如今你要工做在Headless mode下，就不要期望硬件幫忙了，你得自力更生，依靠系統的計算能力模擬出這些特性來。

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

2.4 配置監聽併發布應用啓動事件

SpringApplicationRunListener 負責加載 ApplicationListener事件。

SpringApplicationRunListeners listeners = getRunListeners(args);
// 開始
listeners.starting();
// 處理全部 property sources 配置和 profiles 配置，準備環境，分爲標準 Servlet 環境和標準環境
ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
// 準備應用上下文
prepareContext(context, environment, listeners, applicationArguments,printedBanner);
// 完成
listeners.started(context);
// 異常
handleRunFailure(context, ex, exceptionReporters, listeners);
// 執行
listeners.running(context);
複製代碼

getRunListeners 中根據 type = SpringApplicationRunListener.class 去拿到了全部的 Listener 並根據優先級排序。 對應的就是 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;
	}
複製代碼

在 ApplicationListener 中 , 能夠針對任何一個階段插入處理代碼。

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);

}
複製代碼

3. 每一個階段執行的內容

3.1 listeners.starting();

在加載Spring Application以前執行，全部資源和環境未被加載。

3.2 prepareEnvironment(listeners, applicationArguments);

建立 ConfigurableEnvironment； 將配置的環境綁定到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;
	}
複製代碼

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());
		}
	}
複製代碼

打印日誌-加載的資源

Banner printedBanner = printBanner(environment);
複製代碼

根據不一樣的WebApplicationType建立Context

context = createApplicationContext();
複製代碼

3.4 refreshContext

支持定製刷新

/** * 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();
複製代碼

3.5 afterRefresh

刷新後的實現方法暫未實現

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

3.6 listeners.started(context);

到此爲止， Spring Application的環境和資源都加載完畢了； 發佈應用上下文啓動完成事件； 執行全部 Runner 運行器 - 執行全部 ApplicationRunner 和 CommandLineRunner 這兩種運行器

// 啓動
callRunners(context, applicationArguments);
複製代碼

3.7 listeners.running(context);

觸發全部 SpringApplicationRunListener 監聽器的 running 事件方法