SpringBoot系列二十一：启动配置原理

心已赠人 2022-01-16 06:25 333阅读 0赞

启动流程：  
1、创建SpringApplication对象

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();
    }

![在这里插入图片描述][20190615093111348.png]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpemhpcWlhbmcxMjE3_size_16_color_FFFFFF_t_70]  
2、运行run方法

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  
几个重要的事件回调机制：  
（1）、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

（2）、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));
        }
    }

[20190615093111348.png]: /images/20220114/26274eb33c50484e8cde65d4646b405e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpemhpcWlhbmcxMjE3_size_16_color_FFFFFF_t_70]: /images/20220114/48ab1a3015e54d6c9efa0741bc3f5add.png