Java架构狮

Spring Boot 启动源码解析结合Spring Bean生命周期分析

1.SpringBoot 源码执行流程图

2. 创建SpringApplication 应用，在构造函数中推断启动应用类型，并进行spring boot自动装配

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

查看 SpringApplication 构造函数

　　public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {
        this.sources = new LinkedHashSet();
        // 获取banner打印模式
        this.bannerMode = Mode.CONSOLE;
        this.logStartupInfo = true;
        // 添加命令行系统属性
        this.addCommandLineProperties = true;
        this.addConversionService = true;
        this.headless = true;
        this.registerShutdownHook = true;
        this.additionalProfiles = Collections.emptySet();
        this.isCustomEnvironment = false;
         // 是否懒加载
        this.lazyInitialization = false;
        // 默认赋值 applicationContextFactory 工厂对象
        this.applicationContextFactory = ApplicationContextFactory.DEFAULT;
        this.applicationStartup = ApplicationStartup.DEFAULT;
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
         // 根据类加载路径推断webApplicaitonType类型：SERVLET；REACTIVE
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        // 进行Spring的自动装配，主要用来SpringFactoriesLoader类进行装载工厂
        this.bootstrappers = new ArrayList(this.getSpringFactoriesInstances(Bootstrapper.class));
        this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
         // 设置监听器
        this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }

getSpringFactoriesInstances 方法主要用来进行Spring的自动装配；用 SpringFactoriesLoader类 进行装载工厂，工厂资源位于 META-INF/spring.factories 文件中，这个文件可能在类路径的多个jar文件中。然后调用createSpringFactoriesInstances() 方法对工厂进行实例化并根据注解进行排序。

3.SpringApplication.run方法源码

查看run方法源码

 　　public ConfigurableApplicationContext run(String... args) {
        // 应用启动计时器
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        DefaultBootstrapContext bootstrapContext = this.createBootstrapContext();
        // 初始化应用上下文
        ConfigurableApplicationContext context = null;
        this.configureHeadlessProperty();
        // 获取启动监听器
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        //监听器使用类似于生产-消费模式进行消息监听
        listeners.starting(bootstrapContext, this.mainApplicationClass);

        try {
            //构建应用参数
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //准备应用环境
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            //打印banner
            Banner printedBanner = this.printBanner(environment);
            //创建ApplicationContext
            context = this.createApplicationContext();
            context.setApplicationStartup(this.applicationStartup);
            //准备context
            this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
            //重点：刷新context:实现IOC容器启动的整个过程
            this.refreshContext(context);
            //后置工作
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, listeners);
            throw new IllegalStateException(var10);
        }
        
    }

获取启动监听器。实际上获取的是一个EventPublishingRunListener对象，这个类能通过一个SimpleApplicationEventMulticaster对象广播事件，用到了Executor多线程异步执行框架；

3.1 执行prepareEnvironment 方法，准备应用环境

prepareEnvironment 方法源码

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {
        // 根据前面推断的web环境类型创建推Environment对象
        ConfigurableEnvironment environment = this.getOrCreateEnvironment();
        // 进行环境配置
        this.configureEnvironment((ConfigurableEnvironment)environment, applicationArguments.getSourceArgs());
        ConfigurationPropertySources.attach((Environment)environment);
        listeners.environmentPrepared(bootstrapContext, (ConfigurableEnvironment)environment);
        DefaultPropertiesPropertySource.moveToEnd((ConfigurableEnvironment)environment);
        this.configureAdditionalProfiles((ConfigurableEnvironment)environment);
        this.bindToSpringApplication((ConfigurableEnvironment)environment);
        if (!this.isCustomEnvironment) {
            environment = (new EnvironmentConverter(this.getClassLoader())).convertEnvironmentIfNecessary((ConfigurableEnvironment)environment, this.deduceEnvironmentClass());
        }

        ConfigurationPropertySources.attach((Environment)environment);
        return (ConfigurableEnvironment)environment;
    }

prepareEnvironment 方法主要用来准备应用环境，进行property配置文件解析，profile 环境解析以及获取系统属性和系统环境等；

3.2.1 getOrCreateEnvironment 方法源码

　　private ConfigurableEnvironment getOrCreateEnvironment() {
        if (this.environment != null) {
            return this.environment;
        } else {
            switch(this.webApplicationType) {
            case SERVLET:
                return new StandardServletEnvironment();
            case REACTIVE:
                return new StandardReactiveWebEnvironment();
            default:
                return new StandardEnvironment();
            }
        }
    }

StandardEnvironment的构造器会先对属性源进行定制（将系统属性和系统环境添加到一个MutablePropertySources维护的list中）。这个对象的主要工作包括 property分析、profile相关操作、获取系统属性和系统环境等。

3.2.2 configureEnvironment() 方法获取配置环境

configureEnvironment() 源码：

　　protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
        if (this.addConversionService) {
            ConversionService conversionService = ApplicationConversionService.getSharedInstance();
            environment.setConversionService((ConfigurableConversionService)conversionService);
        }
        // 配置属性源
        this.configurePropertySources(environment, args);
        //获取激活的 profile
        this.configureProfiles(environment, args);
    }

configureProfiles 方法通过AbstractEnvironment#getActiveProfiles() 解析 spring.profile.active 属性，添加到activeProfiles这个集合中。

3.3.createApplicationContext方法

createApplicationContext 方法源码

　　protected ConfigurableApplicationContext createApplicationContext() {
        return this.applicationContextFactory.create(this.webApplicationType);
    }

进入 applicationContextFactory.create 方法的类中，存在一个根据webApplicationType获取容器类型的变量方法如下:

@FunctionalInterface
public interface ApplicationContextFactory {
    // 根据webApplicationType返回指定的容器实例
    applicationContextFactoryApplicationContextFactory DEFAULT = (webApplicationType) -> {
        try {
            switch(webApplicationType) {
            case SERVLET:
                return new AnnotationConfigServletWebServerApplicationContext();
            case REACTIVE:
                return new AnnotationConfigReactiveWebServerApplicationContext();
            default:
                return new AnnotationConfigApplicationContext();
            }
        } catch (Exception var2) {
            throw new IllegalStateException("Unable create a default ApplicationContext instance, you may need a custom ApplicationContextFactory", var2);
        }
    };
      ConfigurableApplicationContext create(WebApplicationType webApplicationType);
}

通过以上方式获取到具体的ApplicationContext实例，并通过构造函数进行实例化，查看构造函数的过程：

3.3.1AnnotationConfigApplicationContext() 的构造方法

构造方法源码如下：

public AnnotationConfigApplicationContext() {
        // 启动上面获取的容器类型实例
        StartupStep createAnnotatedBeanDefReader = this.getApplicationStartup().start("spring.context.annotated-bean-reader.create");
        // 构建AnnotatedBeanDefinitionReader对象
        this.reader = new AnnotatedBeanDefinitionReader(this);
        createAnnotatedBeanDefReader.end();
          // 构建 ClassPathBeanDefinitionScanner对象
        this.scanner = new ClassPathBeanDefinitionScanner(this);
    }

AnnotationConfigApplicationContext的默认构造器会构造一个AnnotationBeanDefinitionReader对象和ClassPathBeanDefinitionScanner对象，在构造AnnotationBeanDefinitionReader对象的过程中会向bean factory添加注解处理器和事件监听处理器BeanDefinition，为后续的配置解析作准备。这样，就能通过JavaConfig 构建 BeanDefinition 并实现自动扫描。

AnnotationConfigApplicationContext的父类GenericApplicationContext的默认构造器会构造一个DefaultListableBeanFactory 对象，这样应用上下文持有一个bean factory的引用，大部分应用只需与应用上下文提供的接口打交道就是因为它对bean factory进行了一层封装。至此，一个Spring容器已经构造出来了，但是目前这个容器还什么都没有，需要根据用户的配置文件进行配置才能按照用户逻辑进行工作。

3.4.prepareContext方法

prepareContext 方法源码

private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
        // 使context持有应用环境的引用，同时将应用环境的引用赋给reader和scanner
        context.setEnvironment(environment);
        // 实现应用上下文的后置处理：主要是注册BeanNameGenerator类型的bean并设置应用上下文的资源加载器和类加载器
        this.postProcessApplicationContext(context);
        // 应用初始化器--添加监听器、logger、warnning、以及spring启动加解密等组件
        this.applyInitializers(context);
        listeners.contextPrepared(context);
        bootstrapContext.close(context);
        if (this.logStartupInfo) {
            this.logStartupInfo(context.getParent() == null);
            this.logStartupProfileInfo(context);
        }

        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        // 添加启动相关的bean
        beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
        // 注册打印banner的bean
        if (printedBanner != null) {
            beanFactory.registerSingleton("springBootBanner", printedBanner);
        }
        // 注册可定义重写的bean
        if (beanFactory instanceof DefaultListableBeanFactory) {
            ((DefaultListableBeanFactory)beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }
        // 添加懒加载的bean工厂后置处理器
        if (this.lazyInitialization) {
            context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
        }
        // Load the sources
        Set