Spring Boot源码（一）

今天又是新的一天，时间过的真快，我真（心）慌（慌）。加油,小菜🦆,🦆 ！

先大致看一下，spring boot 启动到底都干了什么吧

• 入口

// 启动入口方法
public static void main(String[] args) {
        SpringApplication.run(IchatApplication.class, args);
    }

• 进入run()方法

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

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

• 先看一下new SpringApplication(primarySources)

  
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 = new HashSet();
        this.isCustomEnvironment = false;
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        // 保存主配置类
        this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
        // 设置应用类型 NONE,    SERVLET,    REACTIVE;三种类型
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        // 设置初始化器 从类路径下找到 META/INF/Spring.factories 配置的所有 ApplicationContextInitializer，然后保存起来
        this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
        // 设置监听器    从类路径下找到 META/INF/Spring.factories 配置的所有 ApplicationListener，然后保存起来
        this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
        // 从多个配置类中找到有 main 方法的主配置类
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }

primarySources：

• 重点来了 run()方法

public ConfigurableApplicationContext run(String... args) {
        // 计时
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        // 什么IOC容器
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
        this.configureHeadlessProperty();

        // 从类路径下找到 META/INF/Spring.factories 获取 SpringApplicationRunListeners 并启动监听器
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting();

        Collection exceptionReporters;
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            // 准备环境，包括创建环境，创建环境完成后回调 SpringApplicationRunListeners#environmentPrepared()方法，表示环境准备完成
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            // 创建 IOC 容器（决定创建 web 的 IOC 容器还是普通的 IOC 容器）
            context = this.createApplicationContext();
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            // Spring容器前置处理
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            // 刷新容器，IOC 容器初始化（如果是 Web 应用还会创建嵌入式的 Tomcat），扫描、创建、加载所有组件的地方
            this.refreshContext(context);
            // Spring容器后置处理
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }
            // 发出结束执行的事件
            listeners.started(context);
            //  执行Runners
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, exceptionReporters, listeners);
            throw new IllegalStateException(var10);
        }

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