SpringBoot啟動過程的實現
SpringBoot啟動過程分析,首先開啟SpringBoot的啟用入口Main類:
@SpringBootApplication public class ApplicationMain{ public static void main(String[] args) { SpringApplication.run(ApplicationMain.class,args); } }
可以看到main方法裡面只有一行核心啟用類:SpringApplication.run(ApplicationMain.class,args);這個是關鍵,在改行打上斷點,debug模式啟動該main類。點選下一步進入SpringApplication的原始碼對應的run方法:
public static ConfigurableApplicationContext run(Object[] sources,String[] args) { return (new SpringApplication(sources)).run(args); }
初始化SpringApplication
SpringApplication例項化之前會呼叫構造方法進行初始化:
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構造方法的核心是:this.initialize(sources);初始化方法,SpringApplication通過呼叫該方法來初始化。
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方法是用來判斷當前應用的環境,該方法通過獲取這兩個類來判斷當前環境是否是web環境,如果能獲得這兩個類說明是web環境,否則不是。
javax.servlet.Servlet org.springframework.web.context.ConfigurableWebApplicationContext
2.getSpringFactoriesInstances方法主要用來從spring.factories檔案中找出key為ApplicationContextInitializer的類並例項化,然後呼叫setInitializers方法設定到SpringApplication的initializers屬性中。這個過程就是找出所有的應用程式初始化器。
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; }
public static List<String> loadFactoryNames(Class<?> factoryClass,ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); try { //從spring.factories檔案中找出key為ApplicationContextInitializer的類 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); } }
當前的初始化器有如下幾個:
3.同理呼叫getSpringFactoriesInstances從spring.factories檔案中找出key為ApplicationListener的類並例項化,然後呼叫setListeners方法設定到SpringApplication的listeners屬性中。這個過程就是找出所有的應用程式事件監聽器。
當前的事件監聽器有如下幾個:
4.呼叫deduceMainApplicationClass方法找出main類,就是這裡的ApplicationMain類。
執行SpringApplication
初始化SpringApplication完成之後,呼叫run方法執行:
public ConfigurableApplicationContext run(String... args) { //計時器,統計任務的執行時間 StopWatch stopWatch = new StopWatch(); //開始執行 stopWatch.start(); ConfigurableApplicationContext context = null; FailureAnalyzers analyzers = null; this.configureHeadlessProperty(); // 獲取SpringApplicationRunListeners啟動事件監聽器,這裡只有一個EventPublishingRunListener SpringApplicationRunListeners listeners = this.getRunListeners(args); // 封裝成SpringApplicationEvent事件然後廣播出去給SpringApplication中的listeners所監聽 listeners.starting(); try { // 構造一個應用程式引數持有類 ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); // 準備並配置環境 ConfigurableEnvironment environment = this.prepareEnvironment(listeners,applicationArguments); // 列印banner圖形 Banner printedBanner = this.printBanner(environment); // 建立Spring容器 context = this.createApplicationContext(); new FailureAnalyzers(context); // 配置Spring容器 this.prepareContext(context,environment,listeners,applicationArguments,printedBanner); // 容器上下文重新整理 this.refreshContext(context); // 容器建立完成之後呼叫afterRefresh方法 this.afterRefresh(context,applicationArguments); // 呼叫監聽器,廣播Spring啟動結束的事件 listeners.finished(context,(Throwable)null); // 停止計時器 stopWatch.stop(); if (this.logStartupInfo) { (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(),stopWatch); } return context; } catch (Throwable var9) { this.handleRunFailure(context,(FailureAnalyzers)analyzers,var9); throw new IllegalStateException(var9); } }
SpringApplicationRunListeners
1.獲取啟動事件監聽器,可以看看該方法:
SpringApplicationRunListeners listeners = this.getRunListeners(args);
private SpringApplicationRunListeners getRunListeners(String[] args) { Class<?>[] types = new Class[]{SpringApplication.class,String[].class}; return new SpringApplicationRunListeners(logger,this.getSpringFactoriesInstances(SpringApplicationRunListener.class,types,this,args)); }
同樣的通過呼叫getSpringFactoriesInstances方法去META-INF/spring.factories檔案中拿到SpringApplicationRunListener監聽器,當前的SpringApplicationRunListener事件監聽器只有一個EventPublishingRunListener廣播事件監聽器:
SpringApplicationRunListeners內部持有SpringApplicationRunListener集合和1個Log日誌類。用於SpringApplicationRunListener監聽器的批量執行。
SpringApplicationRunListener用於監聽SpringApplication的run方法的執行,它定義了5個步驟:
1.starting:run方法執行的時候立馬執行,對應的事件型別是ApplicationStartedEvent
2.environmentPrepared:ApplicationContext建立之前並且環境資訊準備好的時候呼叫,對應的事件型別是ApplicationEnvironmentPreparedEvent
3.contextPrepared:ApplicationContext建立好並且在source載入之前呼叫一次,沒有具體的對應事件
4.contextLoaded:ApplicationContext建立並載入之後並在refresh之前呼叫,對應的事件型別是ApplicationPreparedEvent
5.finished:run方法結束之前呼叫,對應事件的型別是ApplicationReadyEvent或ApplicationFailedEvent
SpringApplicationRunListener目前只有一個實現類EventPublishingRunListener,詳見獲取SpringApplicationRunListeners。它把監聽的過程封裝成了SpringApplicationEvent事件並讓內部屬性ApplicationEventMulticaster介面的實現類SimpleApplicationEventMulticaster廣播出去,廣播出去的事件物件會被SpringApplication中的listeners屬性進行處理。
所以說SpringApplicationRunListener和ApplicationListener之間的關係是通過ApplicationEventMulticaster廣播出去的SpringApplicationEvent所聯絡起來的
2.啟動事件監聽器
通過listeners.starting()可以啟動事件監聽器SpringApplicationRunListener ,SpringApplicationRunListener 是一個啟動事件監聽器介面:
public interface SpringApplicationRunListener { void starting(); void environmentPrepared(ConfigurableEnvironment var1); void contextPrepared(ConfigurableApplicationContext var1); void contextLoaded(ConfigurableApplicationContext var1); void finished(ConfigurableApplicationContext var1,Throwable var2); }
SpringApplicationRunListener 介面的具體實現就是EventPublishingRunListener類,我們主要來看一下它的startting方法,該方法會封裝成SpringApplicationEvent事件然後廣播出去給SpringApplication中的listeners所監聽。
public void starting() { this.initialMulticaster.multicastEvent(new ApplicationStartedEvent(this.application,this.args)); }
配置並準備環境
private ConfigurableEnvironment prepareEnvironment( SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) { // 建立應用程式的環境資訊。如果是web程式,建立StandardServletEnvironment;否則,建立StandardEnvironment ConfigurableEnvironment environment = getOrCreateEnvironment(); // 配置環境資訊。比如profile,命令列引數 configureEnvironment(environment,applicationArguments.getSourceArgs()); // 廣播出ApplicationEnvironmentPreparedEvent事件給相應的監聽器執行 listeners.environmentPrepared(environment); // 環境資訊的校對 if (!this.webEnvironment) { environment = new EnvironmentConverter(getClassLoader()) .convertToStandardEnvironmentIfNecessary(environment); } return environment; }
判斷環境,如果是web程式,建立StandardServletEnvironment;否則,建立StandardEnvironment。
private ConfigurableEnvironment getOrCreateEnvironment() { if (this.environment != null) { return this.environment; } else { return (ConfigurableEnvironment)(this.webEnvironment ? new StandardServletEnvironment() : new StandardEnvironment()); } }
建立Spring容器上下文
protected ConfigurableApplicationContext createApplicationContext() { Class<?> contextClass = this.applicationContextClass; if (contextClass == null) { try { // 判斷是否是web應用, // 如果是則建立AnnotationConfigEmbeddedWebApplicationContext,否則建立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
private void prepareContext(ConfigurableApplicationContext context,ConfigurableEnvironment environment,SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments,Banner printedBanner) { // 設定Spring容器上下文的環境資訊 context.setEnvironment(environment); // Spring容器建立之後做一些額外的事 postProcessApplicationContext(context); // SpringApplication的初始化器開始工作 applyInitializers(context); // 遍歷呼叫SpringApplicationRunListener的contextPrepared方法。目前只是將這個事件廣播器註冊到Spring容器中 listeners.contextPrepared(context); if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); } // 把應用程式引數持有類註冊到Spring容器中,並且是一個單例 context.getBeanFactory().registerSingleton("springApplicationArguments",applicationArguments); if (printedBanner != null) { context.getBeanFactory().registerSingleton("springBootBanner",printedBanner); } // 載入sources,sources是main方法所在的類 Set<Object> sources = getSources(); Assert.notEmpty(sources,"Sources must not be empty"); // 將sources載入到應用上下文中。最終呼叫的是AnnotatedBeanDefinitionReader.registerBean方法 load(context,sources.toArray(new Object[sources.size()])); // 廣播出ApplicationPreparedEvent事件給相應的監聽器執行 // 執行EventPublishingRunListener.contextLoaded方法 listeners.contextLoaded(context); }
Spring容器建立之後回撥方法postProcessApplicationContext
protected void postProcessApplicationContext(ConfigurableApplicationContext context) { // 如果SpringApplication設定了例項命名生成器,則註冊到Spring容器中 if (this.beanNameGenerator != null) { context.getBeanFactory().registerSingleton( AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR,this.beanNameGenerator); } // 如果SpringApplication設定了資源載入器,設定到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()); } } }
初始化器開始工作
protected void applyInitializers(ConfigurableApplicationContext context) { // 遍歷每個初始化器,呼叫對應的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容器建立完成之後會呼叫afterRefresh方法
ApplicationRunner、CommandLineRunner類都是在在afterRefresh方法中呼叫的,也就是說在Spring容器建立之後執行的。
protected void applyInitializers(ConfigurableApplicationContext context) { // 遍歷每個初始化器,呼叫對應的initialize方法 for (ApplicationContextInitializer initializer : getInitializers()) { Class<?> requiredType = GenericTypeResolver.resolveTypeArgument( initializer.getClass(),"Unable to call initializer."); initializer.initialize(context); } }
參考:https://blog.wangqi.love/articles/Spring/SpringBoot啟動過程.html
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