SpringBoot RUN方法執行流程

1、查看main方法

@SpringBootApplication // 能夠掃描Spring組件並自動配置Spring Boot
public class  SpringbootApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringbootApplication.class, args);
    }
}

2、點進run方法

    public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) { // 調用重載方法
        return run(new Class[]{primarySource}, args);
    }

    public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) { // 兩件事:1.初始化SpringApplication 2.執行run方法
        return (new SpringApplication(primarySources)).run(args);
    }

• 初始化SpringApplication對象
• 執行run方法

3、初始化SpringApplication對象

public SpringApplication(Class<?>... primarySources) {
        this((ResourceLoader)null, primarySources);
    }

    public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        this.sources = new LinkedHashSet();
        this.bannerMode = Mode.CONSOLE;
        this.logStartupInfo = true;
        this.addCommandLineProperties = true;
        this.addConversionService = true;
        this.headless = true;
        this.registerShutdownHook = true;
        this.additionalProfiles = Collections.emptySet();
        this.isCustomEnvironment = false;
        this.lazyInitialization = false;
        this.applicationContextFactory = ApplicationContextFactory.DEFAULT;
        this.applicationStartup = ApplicationStartup.DEFAULT;
        // 設置資源加載器
        this.resourceLoader = resourceLoader;
        // 斷言加載資源類不能為null
        Assert.notNull(primarySources, "PrimarySources must not be null");
        // 將primarySources數組轉換為List，最后放到LinkedHashSet集合中
        this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
        //【1.1 推斷應用類型，后面會根據類型初始化對應的環境。常用的一般都是servlet環境 】
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        this.bootstrapRegistryInitializers = this.getBootstrapRegistryInitializersFromSpringFactories();
				
// 【1.2 初始化classpath下 META-INF/spring.factories中已配置的 ApplicationContextInitializer 】       
      this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
// 【1.3 初始化classpath下所有已配置的 ApplicationListener 】
        this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
// 【1.4 根據調用棧，推斷出 main 方法的類名 】
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }

4、 run(args)源碼剖析

public ConfigurableApplicationContext run(String... args) {
        //記錄程序運行時間
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
  	    // 注解bootstrap 初始化器到BootStrapContext上下文中
        DefaultBootstrapContext bootstrapContext = this.createBootstrapContext();
        ConfigurableApplicationContext context = null;
  			// 設置 java.awt.headless屬性
        this.configureHeadlessProperty();
  			//從META-INF/spring.factories中獲取監聽器 `SpringApplicationRunListener`
        //1、獲取並啟動監聽器
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
  			// 循環遍歷啟動監聽器
        listeners.starting(bootstrapContext, this.mainApplicationClass);

        try {
          
            // 封裝參數對象
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //2、構造應用上下文環境,看構建的是SERVLET、REACTIVE、還是普通環境
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);
            //處理需要忽略的Bean
            this.configureIgnoreBeanInfo(environment);
            //打印banner
            Banner printedBanner = this.printBanner(environment);
            //3、初始化應用上下文
            context = this.createApplicationContext();
            context.setApplicationStartup(this.applicationStartup);
          //4、刷新應用上下文前的准備階段
            this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
          //5、刷新應用上下文
            this.refreshContext(context);
          //刷新應用上下文后的擴展接口
            this.afterRefresh(context, applicationArguments);
          //時間記錄停止
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }
						//發布容器啟動完成事件
            listeners.started(context);
          	// 將ApplicationRunner、CommandLineRunner注入到list里面並排序，然后循環調用Runner的run方法
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, listeners);
            throw new IllegalStateException(var10);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }

以后就是主要分六步

• 第1步：創建並啟動監聽器listener

• 第2步：構建上下文環境，看是創建看構建的是SERVLET、REACTIVE、還是普通環境ApplicationEnvironment

• 第3步：初始化應用上下文

• 第4步：刷新應用上下文前的准備階段，

• 第5步：刷新上下文並且注冊了一個鈎子（JVM關閉就會關閉這個上下文）

• 第6步：刷新應用上下文后的擴展接口，afterRefresh這個是一個空實現的方法