跟我学springboot（二十二）springboot-启动配置原理

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/a303549861/article/details/82780402

1. 启动原理

1、创建SpringApplication对象

initialize(sources);
private void initialize(Object[] sources) {
	//保存主配置类
	if (sources != null && sources.length > 0) {
		this.sources.addAll(Arrays.asList(sources));
	} 
	//判断当前是否一个web应用
	this.webEnvironment = deduceWebEnvironment();
	//从类路径下找到META‐INF/spring.factories配置的所有ApplicationContextInitializer；然后保存起来
	setInitializers((Collection) getSpringFactoriesInstances(
	ApplicationContextInitializer.class));
	//从类路径下找到ETA‐INF/spring.factories配置的所有ApplicationListener
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	//从多个配置类中找到有main方法的主配置类
	this.mainApplicationClass = deduceMainApplicationClass();
}

2.运行流程

public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	FailureAnalyzers analyzers = null;
	configureHeadlessProperty();
	//获取SpringApplicationRunListeners；从类路径下META‐INF/spring.factories
	SpringApplicationRunListeners listeners = getRunListeners(args);
	//回调所有的获取SpringApplicationRunListener.starting()方法
	listeners.starting();
	try {
		//封装命令行参数
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(
		args);
		//准备环境
		ConfigurableEnvironment environment = prepareEnvironment(listeners,
		applicationArguments);
		//创建环境完成后回调SpringApplicationRunListener.environmentPrepared()；表示环境准
		备完成
		Banner printedBanner = printBanner(environment);
		//创建ApplicationContext；决定创建web的ioc还是普通的ioc
		context = createApplicationContext();
		analyzers = new FailureAnalyzers(context);
		//准备上下文环境;将environment保存到ioc中；而且applyInitializers()；
		//applyInitializers()：回调之前保存的所有的ApplicationContextInitializer的initialize方法
		//回调所有的SpringApplicationRunListener的contextPrepared()；
		//
		prepareContext(context, environment, listeners, applicationArguments,
		printedBanner);
		//prepareContext运行完成以后回调所有的SpringApplicationRunListener的contextLoaded（）；
		//s刷新容器；ioc容器初始化（如果是web应用还会创建嵌入式的Tomcat）；Spring注解版
		//扫描，创建，加载所有组件的地方；（配置类，组件，自动配置）
		refreshContext(context);
		//从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调
		//ApplicationRunner先回调，CommandLineRunner再回调
		afterRefresh(context, applicationArguments);
		//所有的SpringApplicationRunListener回调finished方法
		listeners.finished(context, null);
		stopWatch.stop();
		if (this.logStartupInfo) {
			new StartupInfoLogger(this.mainApplicationClass)
			.logStarted(getApplicationLog(), stopWatch);
		}
		//整个SpringBoot应用启动完成以后返回启动的ioc容器；
		return context;
	} catch (Throwable ex) {
		handleRunFailure(context, listeners, analyzers, ex);
		throw new IllegalStateException(ex);
	}
}

3.事件监听机制

配置在META-INF/spring.factories
ApplicationContextInitializer

public class HelloApplicationContextInitializer implements
ApplicationContextInitializer<ConfigurableApplicationContext> {
@Override
public void initialize(ConfigurableApplicationContext applicationContext) {
System.out.println("ApplicationContextInitializer...initialize..."+applicationContext);
}
}

SpringApplicationRunListener

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
//必须有的构造器
public HelloSpringApplicationRunListener(SpringApplication application, String[] args){
} @
Override
public void starting() {
System.out.println("SpringApplicationRunListener...starting...");
} @
Override
public void environmentPrepared(ConfigurableEnvironment environment) {
Object o = environment.getSystemProperties().get("os.name");
System.out.println("SpringApplicationRunListener...environmentPrepared.."+o);
} @
Override
public void contextPrepared(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener...contextPrepared...");
} @
Override
public void contextLoaded(ConfigurableApplicationContext context) {
System.out.println("SpringApplicationRunListener...contextLoaded...");
} @
Override
public void finished(ConfigurableApplicationContext context, Throwable exception) {
System.out.println("SpringApplicationRunListener...finished...");
}
}

配置（META-INF/spring.factories）

org.springframework.context.ApplicationContextInitializer=\
com.atguigu.springboot.listener.HelloApplicationContextInitializer
org.springframework.boot.SpringApplicationRunListener=\
com.atguigu.springboot.listener.HelloSpringApplicationRunListener

只需要放在ioc容器中
ApplicationRunner

@Component
public class HelloApplicationRunner implements ApplicationRunner {
	@Override
	public void run(ApplicationArguments args) throws Exception {
	System.out.println("ApplicationRunner...run....");
}
}

CommandLineRunner

@Component
public class HelloCommandLineRunner implements CommandLineRunner {
	@Override
	public void run(String... args) throws Exception {
	System.out.println("CommandLineRunner...run..."+ Arrays.asList(args));
	}
}