1. SpringApplication

SpringBoot启动流程及各组件相互调用关系如图

1.1. 详解

1.1.1. 无参构造方法调用initialize()方法做初始化动作

/**
 * Create a new SpringApplication instance. The application context will load beans from the specified sources (see class-level documentation for details. The instance can be customized before calling run(String...).
 Params:
 sources – the bean sources
 See Also:
 run(Object, String[]), SpringApplication(ResourceLoader, Object...)
 */
@SuppressWarnings({"unchecked", "rawtypes"})
private void initialize(Object[]sources){
        if(sources!=null&&sources.length>0){
        this.sources.addAll(Arrays.asList(sources));
        }
        //推断当前程序类型
        this.webEnvironment=deduceWebEnvironment();
        //使用SpringFactoriesLoader 实例化所有可用的初始器
        setInitializers((Collection)getSpringFactoriesInstances(ApplicationContextInitializer.class));
        //使用SpringFactoriesLoader 实例化所有可用的监听器
        setListeners((Collection)getSpringFactoriesInstances(ApplicationListener.class));
        //配置应用主方法所在类
        this.mainApplicationClass=deduceMainApplicationClass();
        }

1.1.2. 启动方法run()

run方法完成了spring整个启动过程

    /**
     * Run the Spring application, creating and refreshing a new
     * {@link ApplicationContext}.
     * @param args the application arguments (usually passed from a Java main method)
     * @return a running {@link ApplicationContext}
     */
    public ConfigurableApplicationContext run(String... args) {
        //开启时钟计时
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        FailureAnalyzers analyzers = null;
        //开启设置，让系统模拟不存在io设备
        configureHeadlessProperty();
        //初始化SpringApplicationRunListener 监听器，并进行封装
        SpringApplicationRunListeners listeners = getRunListeners(args);
        listeners.starting();
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            //环境准备
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            //打印banner
            Banner printedBanner = printBanner(environment);
            context = createApplicationContext();
            analyzers = new FailureAnalyzers(context);
            //容器初始化
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);
            //刷新上下文容器
            refreshContext(context);
            afterRefresh(context, applicationArguments);
            listeners.finished(context, null);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass)
                        .logStarted(getApplicationLog(), stopWatch);
            }
            return context;
        }
        catch (Throwable ex) {
            handleRunFailure(context, listeners, analyzers, ex);
            throw new IllegalStateException(ex);
        }
    }

1.1.3. SpringApplicationRunListeners 使用

通过getSpringFactoriesInstances 获取到所有实现SpringApplicationRunListener 接口的实例，默认情况下该接口的实现类只有 EventPublishingRunListener 他的主要作用是作为springboot 的一个广播器

private SpringApplicationRunListeners getRunListeners(String[] args) {
        Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
        return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
                SpringApplicationRunListener.class, types, this, args));
    }