前言

1.springboot的自动装配，是我们可以简单的在主启动类上使用@SpringbootApplication注解
2.main方法SpringApplication调用静态run方法就可以实现实现一个简单的应用

1、主启动类

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

2、SpringApplication

//静态帮助方法
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
	return run(new Class<?>[] { primarySource }, args);
}

//静态run方法重载
//创建SpringApplication实例调用run方法
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
	return new SpringApplication(primarySources).run(args);
}

2.1、实例化SpringApplication做了什么：

基于看过spring的源码，实例化的方法看了一个半小时，大多的时间花在了对于方法的刨根问底；下一次先放一放底层jdk级别的实现；先通流程

2.1.1 SpringApplication实例化过程

解析META-INF/spring.factories过程有spring的两个扩展点：

ApplicationContextInitializer
ApplicationListener

public SpringApplication(Class<?>... primarySources) {
	this(null, primarySources);
}

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
	this.resourceLoader = resourceLoader;
	//检查著启动类
	Assert.notNull(primarySources, "PrimarySources must not be null");
	//资源类存入全局变量primarySources 
	this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
	//检查web应用的类型
	this.webApplicationType = WebApplicationType.deduceFromClasspath();
	/**
	* 解析META-INF/spring.factories文件
	* 1.ApplicationContextInitializer的实现类
	* 2.ApplicationListener的实现类
	*/
	setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	//获取主启动类
	this.mainApplicationClass = deduceMainApplicationClass();
}

2.1.1 实例run方法

public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
	configureHeadlessProperty();

	/**
	* 解析springboot的jar下META-INF/spring.factories文件，需要的类
	* META-INF/spring.factories==>org.springframework.boot.SpringApplicationRunListener下的类
	* EventPublishingRunListener
	*/
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting();
	try {
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
		ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
		configureIgnoreBeanInfo(environment);
		//打印banner
		Banner printedBanner = printBanner(environment);
		context = createApplicationContext();
		exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
				new Class[] { ConfigurableApplicationContext.class }, context);
		prepareContext(context, environment, listeners, applicationArguments, printedBanner);
		//spirng的上下文刷新
		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;
}