createApplicationContext

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陈年老文，不看也罢

createApplicationContext

  • 先来看看之前的run方法
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public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    configureHeadlessProperty();
    SpringApplicationRunListeners listeners = getRunListeners(args);
    listeners.starting();
    try {
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
        configureIgnoreBeanInfo(environment);
        Banner printedBanner = printBanner(environment);
        //这是本文重点
        context = createApplicationContext();
        exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context);
        prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        refreshContext(context);
        afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
        }
        listeners.started(context);
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, listeners);
        throw new IllegalStateException(ex);
    }
    try {
        listeners.running(context);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, null);
        throw new IllegalStateException(ex);
    }
    return context;
    }

createApplicationContext()源码

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protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            switch (this.webApplicationType) {
                case SERVLET:
                    contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
                    break;
                case REACTIVE:
                    contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
                    break;
                default:
                    contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
            }
        }
        catch (ClassNotFoundException ex) {
            throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);
        }
    }
    // 通过反射获取对应类的实例
    return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

根据SpringApplication的webApplicationType来实例化对应的上下文；如果webApplicationType的值是SERVLET，那么实例化AnnotationConfigServletWebServerApplicationContext，如果是REACTIVE则实例化AnnotationConfigReactiveWebServerApplicationContext（响应式编程，后续再看），如果既不是SERVLET、也不是REACTIVE，那么则是默认情况（也就是我们所说的非web引用），实例化AnnotationConfigApplicationContext.
webApplicationType的值就在构造SpringApplition时获取

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public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    //...
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
    //...
}

虽然已经创建了应用上下文，但还只是具有一个骨架（填充了少部分内容,注解的,扫描的等等）
参考1