Spring Boot基础（五）SpringBoot启动流程

 

SpringBoot从主类的main方法中的run方法进入，跳转到Application类中的ConfigurableApplicationContext方法，new了一个SpringApplication对象，并且执行了它的run方法

    public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
        return new SpringApplication(primarySources).run(args);
    }

 

当new一个SprngApplication对象时，调用了SpringApplication的构造方法：

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        
        this.resourceLoader = resourceLoader;
        //判断是否有主类
        Assert.notNull(primarySources, "PrimarySources must not be null");
        //参数放入一个set
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        //判断是否为web环境
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        this.bootstrapRegistryInitializers = new ArrayList<>(getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
        //从配置文件中获取Initializers和Listeners两种监听器的名字
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = deduceMainApplicationClass();
    }

 

执行完构造后，对象初始化完毕，监听器已获取，开始真正执行run方法

public ConfigurableApplicationContext run(String... args) {
        //计时
        long startTime = System.nanoTime();
        DefaultBootstrapContext bootstrapContext = createBootstrapContext();
        ConfigurableApplicationContext context = null;
        configureHeadlessProperty();
        //获取获取所有的RunListener（包括自己定义的）
        SpringApplicationRunListeners listeners = getRunListeners(args);
        //调用所有Listeners的Startting方法
        listeners.starting(bootstrapContext, this.mainApplicationClass);
        try {
            //准备启动，封装参数对象
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //准备环境，
            ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
            configureIgnoreBeanInfo(environment);
            Banner printedBanner = printBanner(environment);
            //开始创建context（即IoC容器）
            context = createApplicationContext();
            context.setApplicationStartup(this.applicationStartup);
            //传入listeners，Initializer被初始化。Ioc已创建完毕，未加载Bean
            prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
            //刷新context，在配置中寻找并创建Bean
            refreshContext(context);
            afterRefresh(context, applicationArguments);
            //计时停止
            Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);
            }
            //执行后，项目启动成功
            listeners.started(context, timeTakenToStartup);
            //回调Runner，即ApplicationRunne 和CommandLineRunner被调用
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, listeners);
            throw new IllegalStateException(ex);
        }
        try {
            Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
            listeners.ready(context, timeTakenToReady);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, null);
            throw new IllegalStateException(ex);
        }
        //返回IoC容器
        return context;
    }

 

Startting方法，旧版是用for-each方法实现：

    void starting(ConfigurableBootstrapContext bootstrapContext, Class<?> mainApplicationClass) {
        doWithListeners("spring.boot.application.starting", (listener) -> listener.starting(bootstrapContext),
                (step) -> {
                    if (mainApplicationClass != null) {
                        step.tag("mainApplicationClass", mainApplicationClass.getName());
                    }
                });
    }