SpringBoot 2.x 框架整体启动流程概览

启动流程

主要分为三步: 1.框架初始化 2. 框架启动 3. 自动化装配

• 框架初始化: new SpringApplication(primarySources).run(args); 调用SpringApplication的构造方法 构造方法中, 执行如下的代码, 进行框架的初始化

  public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {
  		// 1. 配置资源加载器
  		this.resourceLoader = resourceLoader;
  		Assert.notNull(primarySources, "PrimarySources must not be null");
  		// 2.  配置primarySources  
  		this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
  		// 3. 应用环境监测 
  		this.webApplicationType = WebApplicationType.deduceFromClasspath();
  		// 4. 配置系统初始化器 
  		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
  		// 5. 配置应用监听器  
  		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
  		// 6. 配置main 方法所在的类  
  		this.mainApplicationClass = deduceMainApplicationClass();
  	}
  

• 框架启动: SpringApplication 初始化完成后, 调用run方法, 进行框架的启动. run方法如下

  	public ConfigurableApplicationContext run(String... args) {
  	  // 1. 计时器开始计时 
  		StopWatch stopWatch = new StopWatch();
  		stopWatch.start();
  		ConfigurableApplicationContext context = null;
  		Collection exceptionReporters = new ArrayList();
  		// 2. Headless 模式赋值 : 工作在一个没有显示器键盘的环境
  		configureHeadlessProperty();
  		// 3. 发送ApplicationStartingEvent  监听事件 
  		SpringApplicationRunListeners listeners = getRunListeners(args);
  		listeners.starting();
  		try {
  				// 4. 配置环境模块
  			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
  	//  5. 发送 ApplicationEnvironmentPreparedEvent
  			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
  			configureIgnoreBeanInfo(environment);
  			// 6. 打印banner
  			Banner printedBanner = printBanner(environment);
  			// 7. 创建应用上下文对象 
  			context = createApplicationContext();
  			// 8. 初始化失败分析器 
  			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
  					new Class[] { ConfigurableApplicationContext.class }, context);
  					// 9. 关联SpringBoot 组件和应用上下文对象 
  					// 10. 在prepareContext 方法中发送ApplicationContextInitializedEvent 
  			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
  			//  11. 加载sources到context当中
  			 // 12. 发送ApplicationPreparedEvent 
  			 // 13. 刷新上下文
  			refreshContext(context);
  			afterRefresh(context, applicationArguments);
  			// 14. 计时器停止计时 . 
  			stopWatch.stop();
  			if (this.logStartupInfo) {
  				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
  			}
  			// 15. 发送ApplicationStartedEvent事件
  			listeners.started(context);
  			// 16. 调用框架启动扩展类
  			// 17. 发送ApplicationReadyEvent 事件
  			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;
  	}
  

• 自动化装配:

  1. 收集配置文件中的配置工厂类
  2. 加载组件工厂
  3. 注册组件内定义的bean

完整的启动流程图

完整的启动流程图如下. 在线浏览图片 https://www.processon.com/view/link/60c580aa7d9c0879372476bd