springboot

spring-boot-启动配置原理

启动原理、运行流程、自动配置原理

Posted by LQFGH on August 24, 2019

[TOC]

Ⅰ启动流程

重要的四个组件

一：准备环境

  • 执行 ApplicationContextInitializer.initialize 方法
  • 监听器 SpringApplicationRunListener 回调 contextPrepared方法加载主配置类信息
  • 监听器 SpringApplicationRunListener 回调 contextLoaded 方法

ApplicationContextInitializer 和 SpringApplicationRunListener 需要在 META-INF/spring.factories 中定义才能生效

二：刷新启动 IOC 容器

  • 扫描加载容器中所有组件
  • 包括从 META-INF/spring.factories 中获取的所有的 EnableAutoConfiguration 组件

三：回调容器中所有 ApplicationRunner 、CommandLineRunner 组件

四：监听器 SpringApplicationRunListener 回调 finished

Ⅱ创建 SpringApplication 对象

这是一个 spring boot 启动类 run 方法

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public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
		return new SpringApplication(sources).run(args);
}

首先创建了一个 SpringApplication 类，我们看下是怎么创建的

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	public SpringApplication(Object... sources) {
		initialize(sources);
	}

接下来进入 initialize 方法

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	private void initialize(Object[] sources) {
		if (sources != null && sources.length > 0) {
            //保存主配置类
			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();
	}

该方法中分别从所有 spring 的 jar 包的 META-INF/spring.factories 文件中分别获取了 所有类型为ApplicationContextInitializer 和 ApplicationListener 的类添加到当前类中。然后将在方法调用栈中获取了 带有 main 方法的主配置类，也就是我们自己定义的 ConfigurableApplicationContext 类

Ⅲ run 方法启动过程

这段代码就是 spring boot 启动的整个流程

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	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
            //创建环境完成后回调SpringApplicationRunListener.environmentPrepared()；表示环境准备完成
			ConfigurableEnvironment environment = prepareEnvironment(listeners,
					applicationArguments);
			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（）；
            
            //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);
		}
	}

Ⅳ时间监听机制

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

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public class HelloSpringApplicationRunLister implements SpringApplicationRunListener {   
    public HelloSpringApplicationRunLister(SpringApplication application, String[]
                                           args) {}
    @Override
    public void starting() {
        System.out.println("HelloSpringApplicationRunLister...starting...");
    }

    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        System.out.println("HelloSpringApplicationRunLister...environmentPrepared...");
    }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("HelloSpringApplicationRunLister...contextPrepared...");
    }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("HelloSpringApplicationRunLister...contextLoaded...");
    }

    @Override
    public void finished(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("HelloSpringApplicationRunLister...finished...");
    }
}

这里需要注意的是 HelloSpringApplicationRunLister 必须要实现构造方法，参数是固定的 SpringApplication 和 String[]

ApplicationContextInitializer 和 SpringApplicationRunListener 组件需要被配置在 META-INF/spring.factories 才能生效，spring 中的很多组件都是这样配置的

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org.springframework.context.ApplicationContextInitializer=\
com.feng.boot.datajpa.listener.HelloApplicationContextInitializer

org.springframework.boot.SpringApplicationRunListener=\
com.feng.boot.datajpa.listener.HelloSpringApplicationRunLister

ApplicationRunner 和 CommandLineRunner 组件只需要添加到容器中即可生效

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

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

最终执行的顺序是

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HelloSpringApplicationRunLister...starting...
HelloSpringApplicationRunLister...starting...
HelloSpringApplicationRunLister...environmentPrepared...
HelloApplicationContextInitializer...initialize...
HelloSpringApplicationRunLister...contextPrepared...
HelloSpringApplicationRunLister...contextLoaded...
HelloSpringApplicationRunLister...finished...
HelloSpringApplicationRunLister...environmentPrepared...
HelloApplicationContextInitializer...initialize...
HelloSpringApplicationRunLister...contextPrepared...
HelloSpringApplicationRunLister...contextLoaded...
HelloApplicationRunner...run...
HelloCommandLineRunner...run...
HelloSpringApplicationRunLister...finished...
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