通常一個簡單的SpringBoot基礎項目我們會有如下代碼

@SpringBootApplication@RestController@RequestMapping('/')public class Application {public static void main(String[] args) {SpringApplication.run(Application.class, args);}}

值得關注的有SpringApplication.run以及注解@SpringBootApplication

public ConfigurableApplicationContext run(String... args) { // 秒表StopWatch stopWatch = new StopWatch();stopWatch.start();ConfigurableApplicationContext context = null;Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();configureHeadlessProperty();// 獲取監聽器SpringApplicationRunListeners listeners = getRunListeners(args);// 監聽器啟動listeners.starting();try { // application 啟動參數列表ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);// 配置忽略的bean信息configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);// 創建應用上下文context = createApplicationContext();exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,new Class[] { ConfigurableApplicationContext.class }, context); // 準備上下文，裝配beanprepareContext(context, environment, listeners, applicationArguments, printedBanner);// 上下文刷新refreshContext(context);// 刷新后做什么afterRefresh(context, applicationArguments);stopWatch.stop();if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);}// 監聽器開始了listeners.started(context);// 喚醒callRunners(context, applicationArguments);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, listeners);throw new IllegalStateException(ex);}try { // 監聽器正式運行listeners.running(context);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, null);throw new IllegalStateException(ex);}return context;}getRunListeners

獲取監聽器

private SpringApplicationRunListeners getRunListeners(String[] args) {Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };// 獲取 Spring Factory 實例對象return new SpringApplicationRunListeners(logger,getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));}private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {ClassLoader classLoader = getClassLoader();// Use names and ensure unique to protect against duplicates// 讀取 spring.factoriesSet<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 創建SpringFactory實例List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);/** * 排序 {@link Ordered} */AnnotationAwareOrderComparator.sort(instances);return instances;}

createSpringFactoriesInstances

@SuppressWarnings('unchecked') private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) { // 初始化 List<T> instances = new ArrayList<>(names.size()); for (String name : names) { try { // 通過名字創建類的class對象 Class<?> instanceClass = ClassUtils.forName(name, classLoader); Assert.isAssignable(type, instanceClass); // 構造器獲取 Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes); // 創建具體實例 T instance = (T) BeanUtils.instantiateClass(constructor, args); // 加入實例表中 instances.add(instance); } catch (Throwable ex) { throw new IllegalArgumentException('Cannot instantiate ' + type + ' : ' + name, ex); } } return instances; }printBanner

private Banner printBanner(ConfigurableEnvironment environment) {if (this.bannerMode == Banner.Mode.OFF) {return null;}ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader: new DefaultResourceLoader(getClassLoader());// 創建打印器SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);if (this.bannerMode == Mode.LOG) { // 輸出return bannerPrinter.print(environment, this.mainApplicationClass, logger);} // 輸出return bannerPrinter.print(environment, this.mainApplicationClass, System.out);}Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {Banner banner = getBanner(environment);banner.printBanner(environment, sourceClass, out);return new PrintedBanner(banner, sourceClass);}

最終輸出內容類：org.springframework.boot.SpringBootBanner

class SpringBootBanner implements Banner {private static final String[] BANNER = { '', ' . ____ _ __ _ _',' / / ___’_ __ _ _(_)_ __ __ _ ', '( ( )___ | ’_ | ’_| | ’_ / _` | ',' / ___)| |_)| | | | | || (_| | ) ) ) )', ' ’ |____| .__|_| |_|_| |___, | / / / /',' =========|_|==============|___/=/_/_/_/' };private static final String SPRING_BOOT = ' :: Spring Boot :: ';private static final int STRAP_LINE_SIZE = 42;@Overridepublic void printBanner(Environment environment, Class<?> sourceClass, PrintStream printStream) {for (String line : BANNER) {printStream.println(line);}String version = SpringBootVersion.getVersion();version = (version != null) ? ' (v' + version + ')' : '';StringBuilder padding = new StringBuilder();while (padding.length() < STRAP_LINE_SIZE - (version.length() + SPRING_BOOT.length())) {padding.append(' ');}printStream.println(AnsiOutput.toString(AnsiColor.GREEN, SPRING_BOOT, AnsiColor.DEFAULT, padding.toString(),AnsiStyle.FAINT, version));printStream.println();}}

希望通過本篇對于springboot啟動方法的解讀，讓大家對springboot底層有了一個大致了解，只分析了主要方法，希望對大家有幫助

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