最近看springBoot，研究一下springBoot启动源码

springboot启动

• 初始化SpringApplication
• 调用SpringApplication的run方法启动

主入口程序

@SpringBootApplication
public class PracticeBootStarterApplication {
    private static final Logger logger = LoggerFactory.getLogger(PracticeBootStarterApplication.class);

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

    }
}

SpringApplication.java

//第一步调用
public static ConfigurableApplicationContext run(Class<?> primarySource,
            String... args) {
        return run(new Class<?>[] { primarySource }, args);
    }

//第二步调用
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
            String[] args) {
        return new SpringApplication(primarySources).run(args);
    }
    
//第三步调用
public SpringApplication(Class<?>... primarySources) {
    this(null, primarySources);
}


//SpringApplication构造方法
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        //设置resourceLoader 默认时为null
        this.resourceLoader = resourceLoader;
        //判断启动类不为空
        Assert.notNull(primarySources, "PrimarySources must not be null");
        //设置启动类为主source
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        //设置web应用类型，main方法启动时类型为WebApplicationType.SERVLET
        this.webApplicationType = deduceWebApplicationType();
        //设置初始化类实例(从spring-boot-autoconfigure包中META-INF/spring.factoryes配置文件中查找对应的类名)
        setInitializers((Collection) getSpringFactoriesInstances(
                ApplicationContextInitializer.class));
        //设置初始化监听器实例(从spring-boot-autoconfigure包中META-INF/spring.factoryes配置文件中查找对应的类名)
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        //设置主入口
        this.mainApplicationClass = deduceMainApplicationClass();
    }
    
    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        //设置Headless模式(
        //Headless模式是系统的一种配置模式。在系统可能缺少显示设备、键盘或鼠标这些外设的情况下可以使用该模式。
        //Headless模式虽然不是我们愿意见到的，但事实上我们却常常需要在该模式下工作，尤其是服务器端程序开发者。
        //因为服务器（如提供Web服务的主机）往往可能缺少前述设备，但又需要使用他们提供的功能，生成相应的数据，
        //以提供给客户端（如浏览器所在的配有相关的显示设备、键盘和鼠标的主机）。)
        configureHeadlessProperty();
        //获取SpringApplicationRunListener实例(从spring-boot包中META-INF/spring.factoryes配置文件中查找对应的类名)
        SpringApplicationRunListeners listeners = getRunListeners(args);
        //启动监听器
        listeners.starting();
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            //准备启动环境(可理解为把配置文件读取到environment对象中)
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            configureIgnoreBeanInfo(environment);
            //打印banner信息(在environment获取spring.banner.location属性获取banner地址，默认在classpath下的banner.txt)
            Banner printedBanner = printBanner(environment);
            //创建ConfigurableApplicationContext
            context = createApplicationContext();
            //获取异常分析器实例(从spring-boot包中META-INF/spring.factoryes配置文件中查找对应的类名org.springframework.boot.diagnostics.FailureAnalyzers)
            exceptionReporters = getSpringFactoriesInstances(
                    SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
             //设置context的environment、listeners等属性
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);
            //1、刷新Context(调用AbstractApplicationContext的refresh)
            //2、context设置shutdownHook
            refreshContext(context);
            //暂时是空方法，扩展使用
            afterRefresh(context, applicationArguments);
            stopWatch.stop();
            //打印启动时间(单位毫秒)
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass)
                        .logStarted(getApplicationLog(), stopWatch);
            }
            //启动监听器
            listeners.started(context);
            //通过implements ApplicationRunner扩展的spring容器启动时执行的动作
            //下面以MyRunner为例
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
            //分析并打印异常原因
            handleRunFailure(context, ex, exceptionReporters, listeners);
            throw new IllegalStateException(ex);
        }

        try {
            //监听器启动
            listeners.running(context);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, null);
            throw new IllegalStateException(ex);
        }
        return context;
    }

其中refreshContext(context)调用applicationContext的refresh方法

自定义runner

@Component
public class MyRunner implements ApplicationRunner {
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("--123--");
    }
}