SpringBoot啟動(dòng)過(guò)程分析，首先打開(kāi)SpringBoot的啟用入口Main類(lèi)：
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@SpringBootApplicationpublic class ApplicationMain{ public static void main(String[] args) { SpringApplication.run(ApplicationMain.class, args); }} |
可以看到main方法里面只有一行核心啟用類(lèi)：SpringApplication.run(ApplicationMain.class, args);這個(gè)是關(guān)鍵，在改行打上斷點(diǎn)，debug模式啟動(dòng)該main類(lèi)。點(diǎn)擊下一步進(jìn)入SpringApplication的源碼對(duì)應(yīng)的run方法：
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public static ConfigurableApplicationContext run(Object[] sources, String[] args) { return (new SpringApplication(sources)).run(args); } |
初始化SpringApplication
SpringApplication實(shí)例化之前會(huì)調(diào)用構(gòu)造方法進(jìn)行初始化：
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public SpringApplication(Object... sources) { this.bannerMode = Mode.CONSOLE; this.logStartupInfo = true; this.addCommandLineProperties = true; this.headless = true; this.registerShutdownHook = true; this.additionalProfiles = new HashSet(); this.initialize(sources); } |
而SpringApplication構(gòu)造方法的核心是：this.initialize(sources);初始化方法，SpringApplication通過(guò)調(diào)用該方法來(lái)初始化。
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private void initialize(Object[] sources) { if (sources != null && sources.length > 0) { this.sources.addAll(Arrays.asList(sources)); } this.webEnvironment = deduceWebEnvironment(); setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); this.mainApplicationClass = deduceMainApplicationClass();} |
1.deduceWebEnvironment方法是用來(lái)判斷當(dāng)前應(yīng)用的環(huán)境，該方法通過(guò)獲取這兩個(gè)類(lèi)來(lái)判斷當(dāng)前環(huán)境是否是web環(huán)境，如果能獲得這兩個(gè)類(lèi)說(shuō)明是web環(huán)境，否則不是。
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javax.servlet.Servletorg.springframework.web.context.ConfigurableWebApplicationContext |
2.getSpringFactoriesInstances方法主要用來(lái)從spring.factories文件中找出key為ApplicationContextInitializer的類(lèi)并實(shí)例化，然后調(diào)用setInitializers方法設(shè)置到SpringApplication的initializers屬性中。這個(gè)過(guò)程就是找出所有的應(yīng)用程序初始化器。
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private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); AnnotationAwareOrderComparator.sort(instances); return instances; } |
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public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); try { //從spring.factories文件中找出key為ApplicationContextInitializer的類(lèi) Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories"); ArrayList result = new ArrayList(); while(urls.hasMoreElements()) { URL url = (URL)urls.nextElement(); Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url)); String factoryClassNames = properties.getProperty(factoryClassName); result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames))); } return result; } catch (IOException var8) { throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + "META-INF/spring.factories" + "]", var8); } } |
當(dāng)前的初始化器有如下幾個(gè):
3.同理調(diào)用getSpringFactoriesInstances從spring.factories文件中找出key為ApplicationListener的類(lèi)并實(shí)例化，然后調(diào)用setListeners方法設(shè)置到SpringApplication的listeners屬性中。這個(gè)過(guò)程就是找出所有的應(yīng)用程序事件監(jiān)聽(tīng)器。
當(dāng)前的事件監(jiān)聽(tīng)器有如下幾個(gè)：
4.調(diào)用deduceMainApplicationClass方法找出main類(lèi)，就是這里的ApplicationMain類(lèi)。
運(yùn)行SpringApplication
初始化SpringApplication完成之后，調(diào)用run方法運(yùn)行：
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public ConfigurableApplicationContext run(String... args) { //計(jì)時(shí)器，統(tǒng)計(jì)任務(wù)的執(zhí)行時(shí)間 StopWatch stopWatch = new StopWatch(); //開(kāi)始執(zhí)行 stopWatch.start(); ConfigurableApplicationContext context = null; FailureAnalyzers analyzers = null; this.configureHeadlessProperty(); // 獲取SpringApplicationRunListeners啟動(dòng)事件監(jiān)聽(tīng)器，這里只有一個(gè)EventPublishingRunListener SpringApplicationRunListeners listeners = this.getRunListeners(args); // 封裝成SpringApplicationEvent事件然后廣播出去給SpringApplication中的listeners所監(jiān)聽(tīng) listeners.starting(); try { // 構(gòu)造一個(gè)應(yīng)用程序參數(shù)持有類(lèi) ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); // 準(zhǔn)備并配置環(huán)境 ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments); // 打印banner圖形 Banner printedBanner = this.printBanner(environment); // 創(chuàng)建Spring容器 context = this.createApplicationContext(); new FailureAnalyzers(context); // 配置Spring容器 this.prepareContext(context, environment, listeners, applicationArguments, printedBanner); // 容器上下文刷新 this.refreshContext(context); // 容器創(chuàng)建完成之后調(diào)用afterRefresh方法 this.afterRefresh(context, applicationArguments); // 調(diào)用監(jiān)聽(tīng)器，廣播Spring啟動(dòng)結(jié)束的事件 listeners.finished(context, (Throwable)null); // 停止計(jì)時(shí)器 stopWatch.stop(); if (this.logStartupInfo) { (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch); } return context; } catch (Throwable var9) { this.handleRunFailure(context, listeners, (FailureAnalyzers)analyzers, var9); throw new IllegalStateException(var9); } } |
SpringApplicationRunListeners
1.獲取啟動(dòng)事件監(jiān)聽(tīng)器，可以看看該方法：
SpringApplicationRunListeners listeners = this.getRunListeners(args);
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private SpringApplicationRunListeners getRunListeners(String[] args) { Class<?>[] types = new Class[]{SpringApplication.class, String[].class}; return new SpringApplicationRunListeners(logger, this.getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args)); } |
同樣的通過(guò)調(diào)用getSpringFactoriesInstances方法去META-INF/spring.factories文件中拿到SpringApplicationRunListener監(jiān)聽(tīng)器，當(dāng)前的SpringApplicationRunListener事件監(jiān)聽(tīng)器只有一個(gè)EventPublishingRunListener廣播事件監(jiān)聽(tīng)器：
SpringApplicationRunListeners內(nèi)部持有SpringApplicationRunListener集合和1個(gè)Log日志類(lèi)。用于SpringApplicationRunListener監(jiān)聽(tīng)器的批量執(zhí)行。
SpringApplicationRunListener用于監(jiān)聽(tīng)SpringApplication的run方法的執(zhí)行，它定義了5個(gè)步驟：
1.starting：run方法執(zhí)行的時(shí)候立馬執(zhí)行，對(duì)應(yīng)的事件類(lèi)型是ApplicationStartedEvent
2.environmentPrepared：ApplicationContext創(chuàng)建之前并且環(huán)境信息準(zhǔn)備好的時(shí)候調(diào)用，對(duì)應(yīng)的事件類(lèi)型是ApplicationEnvironmentPreparedEvent
3.contextPrepared：ApplicationContext創(chuàng)建好并且在source加載之前調(diào)用一次，沒(méi)有具體的對(duì)應(yīng)事件
4.contextLoaded：ApplicationContext創(chuàng)建并加載之后并在refresh之前調(diào)用，對(duì)應(yīng)的事件類(lèi)型是ApplicationPreparedEvent
5.finished：run方法結(jié)束之前調(diào)用，對(duì)應(yīng)事件的類(lèi)型是ApplicationReadyEvent或ApplicationFailedEvent
SpringApplicationRunListener目前只有一個(gè)實(shí)現(xiàn)類(lèi)EventPublishingRunListener，詳見(jiàn)獲取SpringApplicationRunListeners。它把監(jiān)聽(tīng)的過(guò)程封裝成了SpringApplicationEvent事件并讓內(nèi)部屬性ApplicationEventMulticaster接口的實(shí)現(xiàn)類(lèi)SimpleApplicationEventMulticaster廣播出去，廣播出去的事件對(duì)象會(huì)被SpringApplication中的listeners屬性進(jìn)行處理。
所以說(shuō)SpringApplicationRunListener和ApplicationListener之間的關(guān)系是通過(guò)ApplicationEventMulticaster廣播出去的SpringApplicationEvent所聯(lián)系起來(lái)的
2.啟動(dòng)事件監(jiān)聽(tīng)器
通過(guò)listeners.starting()可以啟動(dòng)事件監(jiān)聽(tīng)器SpringApplicationRunListener ，SpringApplicationRunListener 是一個(gè)啟動(dòng)事件監(jiān)聽(tīng)器接口：
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public interface SpringApplicationRunListener { void starting(); void environmentPrepared(ConfigurableEnvironment var1); void contextPrepared(ConfigurableApplicationContext var1); void contextLoaded(ConfigurableApplicationContext var1); void finished(ConfigurableApplicationContext var1, Throwable var2);} |
SpringApplicationRunListener 接口的具體實(shí)現(xiàn)就是EventPublishingRunListener類(lèi)，我們主要來(lái)看一下它的startting方法，該方法會(huì)封裝成SpringApplicationEvent事件然后廣播出去給SpringApplication中的listeners所監(jiān)聽(tīng)。
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public void starting() { this.initialMulticaster.multicastEvent(new ApplicationStartedEvent(this.application, this.args)); } |
配置并準(zhǔn)備環(huán)境
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private ConfigurableEnvironment prepareEnvironment( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { // 創(chuàng)建應(yīng)用程序的環(huán)境信息。如果是web程序，創(chuàng)建StandardServletEnvironment；否則，創(chuàng)建StandardEnvironment ConfigurableEnvironment environment = getOrCreateEnvironment(); // 配置環(huán)境信息。比如profile，命令行參數(shù) configureEnvironment(environment, applicationArguments.getSourceArgs()); // 廣播出ApplicationEnvironmentPreparedEvent事件給相應(yīng)的監(jiān)聽(tīng)器執(zhí)行 listeners.environmentPrepared(environment); // 環(huán)境信息的校對(duì) if (!this.webEnvironment) { environment = new EnvironmentConverter(getClassLoader()) .convertToStandardEnvironmentIfNecessary(environment); } return environment;} |
判斷環(huán)境，如果是web程序，創(chuàng)建StandardServletEnvironment；否則，創(chuàng)建StandardEnvironment。
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private ConfigurableEnvironment getOrCreateEnvironment() { if (this.environment != null) { return this.environment; } else { return (ConfigurableEnvironment)(this.webEnvironment ? new StandardServletEnvironment() : new StandardEnvironment()); } } |
創(chuàng)建Spring容器上下文
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protected ConfigurableApplicationContext createApplicationContext() { Class<?> contextClass = this.applicationContextClass; if (contextClass == null) { try { // 判斷是否是web應(yīng)用， // 如果是則創(chuàng)建AnnotationConfigEmbeddedWebApplicationContext，否則創(chuàng)建AnnotationConfigApplicationContext contextClass = Class.forName(this.webEnvironment ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS); } catch (ClassNotFoundException ex) { throw new IllegalStateException( "Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass", ex); } } return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);} |
配置Spring容器上下文
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private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) { // 設(shè)置Spring容器上下文的環(huán)境信息 context.setEnvironment(environment); // Spring容器創(chuàng)建之后做一些額外的事 postProcessApplicationContext(context); // SpringApplication的初始化器開(kāi)始工作 applyInitializers(context); // 遍歷調(diào)用SpringApplicationRunListener的contextPrepared方法。目前只是將這個(gè)事件廣播器注冊(cè)到Spring容器中 listeners.contextPrepared(context); if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); } // 把應(yīng)用程序參數(shù)持有類(lèi)注冊(cè)到Spring容器中，并且是一個(gè)單例 context.getBeanFactory().registerSingleton("springApplicationArguments", applicationArguments); if (printedBanner != null) { context.getBeanFactory().registerSingleton("springBootBanner", printedBanner); } // 加載sources，sources是main方法所在的類(lèi) Set<Object> sources = getSources(); Assert.notEmpty(sources, "Sources must not be empty"); // 將sources加載到應(yīng)用上下文中。最終調(diào)用的是AnnotatedBeanDefinitionReader.registerBean方法 load(context, sources.toArray(new Object[sources.size()])); // 廣播出ApplicationPreparedEvent事件給相應(yīng)的監(jiān)聽(tīng)器執(zhí)行 // 執(zhí)行EventPublishingRunListener.contextLoaded方法 listeners.contextLoaded(context);} |
Spring容器創(chuàng)建之后回調(diào)方法postProcessApplicationContext
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protected void postProcessApplicationContext(ConfigurableApplicationContext context) { // 如果SpringApplication設(shè)置了實(shí)例命名生成器，則注冊(cè)到Spring容器中 if (this.beanNameGenerator != null) { context.getBeanFactory().registerSingleton( AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, this.beanNameGenerator); } // 如果SpringApplication設(shè)置了資源加載器，設(shè)置到Spring容器中 if (this.resourceLoader != null) { if (context instanceof GenericApplicationContext) { ((GenericApplicationContext) context) .setResourceLoader(this.resourceLoader); } if (context instanceof DefaultResourceLoader) { ((DefaultResourceLoader) context) .setClassLoader(this.resourceLoader.getClassLoader()); } }} |
初始化器開(kāi)始工作
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protected void applyInitializers(ConfigurableApplicationContext context) { // 遍歷每個(gè)初始化器，調(diào)用對(duì)應(yīng)的initialize方法 for (ApplicationContextInitializer initializer : getInitializers()) { Class<?> requiredType = GenericTypeResolver.resolveTypeArgument( initializer.getClass(), ApplicationContextInitializer.class); Assert.isInstanceOf(requiredType, context, "Unable to call initializer."); initializer.initialize(context); }} |
Spring容器創(chuàng)建完成之后會(huì)調(diào)用afterRefresh方法
ApplicationRunner、CommandLineRunner類(lèi)都是在在afterRefresh方法中調(diào)用的，也就是說(shuō)在Spring容器創(chuàng)建之后執(zhí)行的。
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protected void applyInitializers(ConfigurableApplicationContext context) { // 遍歷每個(gè)初始化器，調(diào)用對(duì)應(yīng)的initialize方法 for (ApplicationContextInitializer initializer : getInitializers()) { Class<?> requiredType = GenericTypeResolver.resolveTypeArgument( initializer.getClass(), ApplicationContextInitializer.class); Assert.isInstanceOf(requiredType, context, "Unable to call initializer."); initializer.initialize(context); }} |
參考：https://blog.wangqi.love/articles/Spring/SpringBoot啟動(dòng)過(guò)程.html
到此這篇關(guān)于SpringBoot啟動(dòng)過(guò)程的實(shí)現(xiàn)的文章就介紹到這了,更多相關(guān)SpringBoot啟動(dòng)過(guò)程內(nèi)容請(qǐng)搜索服務(wù)器之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持服務(wù)器之家！
原文鏈接：https://blog.csdn.net/chengbinbbs/article/details/88557162
