SpringBoot的启动流程分析(2)

我们来分析SpringApplication启动流程中的run()方法,代码如下

    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        FailureAnalyzers analyzers = null;
        configureHeadlessProperty();
        SpringApplicationRunListeners listeners = getRunListeners(args);
        listeners.starting();
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            Banner printedBanner = printBanner(environment);
            context = createApplicationContext();
            analyzers = new FailureAnalyzers(context);
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);
            refreshContext(context);
            afterRefresh(context, applicationArguments);
            listeners.finished(context, null);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass)
                        .logStarted(getApplicationLog(), stopWatch);
            }
            return context;
        }
        catch (Throwable ex) {
            handleRunFailure(context, listeners, analyzers, ex);
            throw new IllegalStateException(ex);
        }
    }

看起来方法比较长，不过我们主要看启动流程，哪些监控，失败分析的我们以后再说，所以这个方法中关键的几步如下

1 context = createApplicationContext();
2 prepareContext(context,environment,listeners,applicationArguments,printedBanner);
3 refreshContext(context);
4 afterRefresh(context, applicationArguments);

没错，看到关键的方法就是这4个，我们首先分析 createApplicationContext()方法，代码如下

　　public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework."
            + "boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext";
    public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
            + "annotation.AnnotationConfigApplicationContext";


    protected ConfigurableApplicationContext createApplicationContext() {
        Class contextClass = this.applicationContextClass;
        if (contextClass == null) {
            try {
                contextClass = Class.forName(this.webEnvironment
                        ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS);
            }
            catch (ClassNotFoundException ex) {
                throw new IllegalStateException(
                        "Unable create a default ApplicationContext, "
                                + "please specify an ApplicationContextClass",
                        ex);
            }
        }
        return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);
    }

很明显，在web环境下它加载并创建了 ConfigurableApplicationContext,简单点说就是创建了ApplicationContext,即创建了Bean的容器(BeanFactory)

然后看 prepareContext()方法，可以看出，这个方法是将配置，参数，监听器，以及banner信息注入applicationContext中

    private void prepareContext(ConfigurableApplicationContext context,
            ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments, Banner printedBanner) {
        context.setEnvironment(environment);
        postProcessApplicationContext(context);
        applyInitializers(context);
        listeners.contextPrepared(context);
        if (this.logStartupInfo) {
            logStartupInfo(context.getParent() == null);
            logStartupProfileInfo(context);
        }

        // Add boot specific singleton beans
        context.getBeanFactory().registerSingleton("springApplicationArguments",
                applicationArguments);
        if (printedBanner != null) {
            context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
        }

        // Load the sources
        Set