spring boot 源码解析 启动流程

在面试过程中经常被问到过spring boot的启动流程，今天就翻一下源码整体看一下；

首先，新建一个启动类，可以看到是首先调用的SpringApplication的静态方法run

@SpringBootApplicationpublic class SourceReadApplillcation {    public static void main(String[] args) {        SpringApplication.run(SourceReadApplillcation.class,args);    }}

1. 这里传入启动类的class，然后调用SpringApplication的构造函数new一个实例，接着调用run方法；

public static ConfigurableApplicationContext run(Class
     primarySource,            String... args) {        return run(new Class
    [] { primarySource }, args);}

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

public SpringApplication(Class
    ... primarySources) {        this(null, primarySources);}    @SuppressWarnings({ "unchecked", "rawtypes" })public SpringApplication(ResourceLoader resourceLoader, Class
    ... primarySources) {    this.resourceLoader = resourceLoader;        Assert.notNull(primarySources, "PrimarySources must not be null");    this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));    //推断web应用类型；    this.webApplicationType = WebApplicationType.deduceFromClasspath();    //设置初始化器，从META-INF/spring.factories读取ApplicationContextInitializer    //配置的值，读取详情后续研究    setInitializers((Collection) getSpringFactoriesInstances(            ApplicationContextInitializer.class));    //设置监听器，同上，读取ApplicationListener配置的值    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));    //设置应用main启动类    this.mainApplicationClass = deduceMainApplicationClass();}

负责启动SpringBoot的主要方法

public ConfigurableApplicationContext run(String... args) {    //计时器，主要为了统计消耗时间    StopWatch stopWatch = new StopWatch();    stopWatch.start();        //初始化应用上下文和异常报告集合    ConfigurableApplicationContext context = null;    Collection
    
      exceptionReporters = new ArrayList<>();        //设置java.awt.headless模式为true    onfigureHeadlessProperty();        //设置并启动META-INF/spring.factories下SpringApplicationRunListener配置的监听器    //这里为EventPublishingRunListener，会通过反射调用其构造函数进行初始化    //并将一开始设置的监听器保存到AbstractApplicationEventMulticaster的    //内部类ListenerRetriever中，详情后续    SpringApplicationRunListeners listeners = getRunListeners(args);    //触发监听器开始启动事件    listeners.starting();    try {        //初始化应用参数，例如启动设置的命令行参数等，可以通过这个类获取        ApplicationArguments applicationArguments = new DefaultApplicationArguments(                args);        //准备运行环境        ConfigurableEnvironment environment = prepareEnvironment(listeners,                applicationArguments);        configureIgnoreBeanInfo(environment);        //打印banner        Banner printedBanner = printBanner(environment);        //创建上下文，Springboot默认为AnnotationConfigApplicationContext        context = createApplicationContext();        //准备异常报告        exceptionReporters = getSpringFactoriesInstances(                SpringBootExceptionReporter.class,                new Class[] { ConfigurableApplicationContext.class }, context);        //准备上下文        prepareContext(context, environment, listeners, applicationArguments,                printedBanner);        //刷新上下文        refreshContext(context);        //上下文刷新后置处理(空方法)        afterRefresh(context, applicationArguments);        //计时统计结束        stopWatch.stop();                if (this.logStartupInfo) {            new StartupInfoLogger(this.mainApplicationClass)                    .logStarted(getApplicationLog(), stopWatch);        }        //触发启动完成事件        listeners.started(context);        callRunners(context, applicationArguments);    }    catch (Throwable ex) {        handleRunFailure(context, ex, exceptionReporters, listeners);        throw new IllegalStateException(ex);    }    try {        //触发运行事件        listeners.running(context);    }    catch (Throwable ex) {        handleRunFailure(context, ex, exceptionReporters, null);        throw new IllegalStateException(ex);    }    return context;}
    

整个启动流程大体就是这样，先有一个整体的概念，其中实现细节很庞杂，后续逐一研究