springboot启动流程简述

 

springboot启动流程简述

程序入口

@SpringBootApplication
public class App {
    public static void main(String[] args) {
    SpringApplication application = new SpringApplication(AppServer.class);
    application.run(args);
    }
}

SpringApplication 构造函数：
初始化上下文的各种接口，实例化监听器

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
   this.resourceLoader = resourceLoader;
   Assert.notNull(primarySources, "PrimarySources must not be null");
   this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
   this.webApplicationType = WebApplicationType.deduceFromClasspath();
   setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
   setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
   this.mainApplicationClass = deduceMainApplicationClass();
}

run方法
1、开启一个秒表统计启动时间并打印日志
2、初始化监听器，启动监听
3、新建和获取当前的Environment实例：
封装main方法的参数，初始化参数，写入到 Environment中，发布 ApplicationEnvironmentPreparedEvent（环境事件），做一些绑定后返回Environment。
4、创建上下文实例：
加载创建的上下文实例，加载中，先填充Environment环境和设置的参数，如果application有设置beanNameGenerator（bean）、resourceLoader（加载器）就将其注入到上下文中
调用初始化的切面，发布ApplicationContextInitializedEvent（上下文初始化）事件；
5、刷新上下文。在刷新上下文里面，做一些，切面方法的调用，注册切面bean，listener注册（ 到广播器中），清理缓存等。
6、发布启动完成的事件，并调用监听者的方法。
（方法调用的细节这里没有点击进去一步步描述，只是自己的一点理解，有错误欢迎指正，谢谢）

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);
      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;
}