Spring Boot深入理解SpringApplication.run()方法启动

我们知道spring boot项目启动，只需要启动@SpringBootApplication.calss中的含有SpringApplication.run()方法的main方法就可以

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

我们下面来看看Spring Boot应用是怎么启动的。

SpringApplication的启动流程

SpringApplication的启动过程非常复杂，下面是在调用SpringApplication.run方法之后启动的关键动作：

既然要了解原理，最直接的方式当然是看源码：

SpringApplication.class

public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
        this.configureHeadlessProperty();
        //初始化监听器
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        //发布ApplicationStartingEvent
        listeners.starting();

        try {
            //装配参数和环境
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //发布ApplicationEnvironmentPreparedEvent
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            //创建ApplicationContext,并装配
            context = this.createApplicationContext();
            this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            //发布ApplicationPreparedEvent
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }
            
            //发布ApplicationStartedEvent
            listeners.started(context);
            //执行Spring中@Bean下的一些操作，如静态方法等
            this.callRunners(context, applicationArguments);
        } catch (Throwable var9) {
            this.handleRunFailure(context, listeners, exceptionReporters, var9);
            throw new IllegalStateException(var9);
        }

        //发布ApplicationReadyEvent
        listeners.running(context);
        return context;
    }