1 启动配置原理

1.1 创建SpringApplication对象

    @SuppressWarnings({ "unchecked", "rawtypes" })
    private void initialize(Object[] sources) {
        //保存主配置类
        if (sources != null && sources.length > 0) {
            this.sources.addAll(Arrays.asList(sources));
        }
        //判断当前是否是一个web应用
        this.webEnvironment = deduceWebEnvironment();
        //从类路径下找到META‐INF/spring.factories配置的所有ApplicationContextInitializer然后保存起来
        setInitializers((Collection) getSpringFactoriesInstances(
                ApplicationContextInitializer.class));
        //从类路径下找到META‐INF/spring.factories配置的所有ApplicationListener然后保存起来
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        //从多个配置类中找到有main方法的主配置类
        this.mainApplicationClass = deduceMainApplicationClass();
    }

1.2 运行run方法

    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        FailureAnalyzers analyzers = null;
        configureHeadlessProperty();
        //获取SpringApplicationRunListeners，从类路径下找到META‐INF/spring.factories配置的所有SpringApplicationRunListeners
        SpringApplicationRunListeners listeners = getRunListeners(args);
        //回调所有的获取SpringApplicationRunListeners.starting();方法
        listeners.starting();
        try {
            //封装命令行参数
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            //准备环境  创建环境完成后回调SpringApplicationRunListener的environmentPrepared()方法，表示环境准备完成
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            Banner printedBanner = printBanner(environment);
            //创建ApplicationContext，决定创建web的IOC容器还是普通的IOC容器
            context = createApplicationContext();
            analyzers = new FailureAnalyzers(context);
            //准备上下文环境
            //将environment保存到ioc容器中;
            //applyInitializers(context); 回调之前报错的所有的ApplicationContextInitializer的initialize方法
            //回调所有的SpringApplicationRunListener的contextPrepared()方法
            //listeners.contextLoaded(context);   回调所有的SpringApplicationRunListener的contextLoaded方法
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);
            //刷新容器：IOC容器初始化流程。
            refreshContext(context);
            //从IOC容器中获取所有的ApplicationRunner和CommandLineRunner进行回调
            //ApplicationRunner先回调
            //CommandLineRunner再回调
            afterRefresh(context, applicationArguments);
            //所有的SpringApplicationRunListene回调finished方法
            listeners.finished(context, null);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass)
                        .logStarted(getApplicationLog(), stopWatch);
            }
            //整个SpringBoot应用启动完成以后返回IOC容器
            return context;
        }
        catch (Throwable ex) {
            handleRunFailure(context, listeners, analyzers, ex);
            throw new IllegalStateException(ex);
        }
    }

• 总结：
• ApplicationContextInitializer和SpringApplicationRunListener需要配置在META‐INF/spring.factories中。
• ApplicationRunner和CommandLineRunner需要放在IOC容器中。

2 自定义starter

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原文地址：https://www.cnblogs.com/xuweiweiwoaini/p/12272538.html