Spring Boot启动流程

一、一行代码完成启动

@SpringBootApplication
public class Sb2Application {

	public static void main(String[] args) {
		SpringApplication.run(Sb2Application.class, args);
	}

}

　　

进入SpringApplication的run方法

SpringApplication.run(Sb2Application.class, args);

分为两步： 一步是初始化SpringApplication, new SpringApplication，第二步是调用SpringApplication的run方法

第一步：初始化SpringApplication

 public SpringApplication(Class... primarySources) {
        this((ResourceLoader)null, primarySources);
    }

    public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {
        this.sources = new LinkedHashSet();
        this.bannerMode = Mode.CONSOLE;
        this.logStartupInfo = true;
        this.addCommandLineProperties = true;
        this.addConversionService = true;
        this.headless = true;
        this.registerShutdownHook = true;
        this.additionalProfiles = new HashSet();
        this.isCustomEnvironment = false;
        this.lazyInitialization = false;
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
        this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }

　　

第二步 调用SpringApplication的run方法

/**
	 * Run the Spring application, creating and refreshing a new
	 * {@link ApplicationContext}.
	 * @param args the application arguments (usually passed from a Java main method)
	 * @return a running {@link ApplicationContext}
	 */
	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;
	}

　

二、启动流程

1、框架初始化

2、框架启动

3、自动化装配

　

1、框架初始化步骤

框架初始化步骤：

配置资源加载器

配置primarySources

应用环境检测

配置系统初始化器

配置应用监听器

配置main方法所在的类

2、框架启动流程

计时器开始计时 -> Headless模式赋值 ->  发送ApplicationStartEvent

-> 配置环境模块 -> 发送ApplicationEnvironmentPreparedEvent

-> 打印banner（打印出来的Spring 1.X 或者Spring 2.X条幅）

-> 创建应用上下文对象 -> 初始化失败分析器

-> 关联springboot组件与应用上下文对象 -> 发送ApplicationContextInitializedEvent

-> 加载source到context -> 发送ApplicationPreparedEvent

-> 刷新上下文（调用Spring框架的DoRefresh方法）

->计时器停止计时 -> 发送ApplicationStartedEvent

-> 调用框架启动扩展类 -> 发送ApplicationReadyEvent

3、自动化装配

收集配置文件中的配置工厂类

加载组件工厂

注册组件内定义bean

Spring Boot的完整流程图