1. SpringBoot中怎么启动Tomcat?

1.1 ServletWebServerFactoryAutoConfiguration

配置Servlet web容器。

@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
      ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
      ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
      ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
}

ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class 导入 WebServerFactoryCustomizerBeanPostProcessor组件，web服务工厂定制器的后置增强

导入了三种不同的web服务器（Tomcat、Jetty、Undertow），默认是Tomcat

我们来看一下 EmbeddedTomcat:

@Configuration(proxyBeanMethods = false)
class ServletWebServerFactoryConfiguration {

   @Configuration(proxyBeanMethods = false)
   @ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
   @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
   static class EmbeddedTomcat {

      @Bean
      TomcatServletWebServerFactory tomcatServletWebServerFactory(
            ObjectProvider<TomcatConnectorCustomizer> connectorCustomizers,
            ObjectProvider<TomcatContextCustomizer> contextCustomizers,
            ObjectProvider<TomcatProtocolHandlerCustomizer<?>> protocolHandlerCustomizers) {
         TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
         factory.getTomcatConnectorCustomizers()
               .addAll(connectorCustomizers.orderedStream().collect(Collectors.toList()));
         factory.getTomcatContextCustomizers()
               .addAll(contextCustomizers.orderedStream().collect(Collectors.toList()));
         factory.getTomcatProtocolHandlerCustomizers()
               .addAll(protocolHandlerCustomizers.orderedStream().collect(Collectors.toList()));
         return factory;
      }

   }
}

tomcatServletWebServerFactory()方法中的参数都是从容器中获取，我们可以自定义直接放到容器中。实现ServletWebServerFactory 接口,该接口的getWebServlet()方法就是创建
Tomcat容器。

1.2 DispatcherServletAutoConfiguration

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {

  
   public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";

   public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

   @Configuration(proxyBeanMethods = false)
   @Conditional(DefaultDispatcherServletCondition.class)
   @ConditionalOnClass(ServletRegistration.class)
   @EnableConfigurationProperties(WebMvcProperties.class)
   protected static class DispatcherServletConfiguration {

      @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
      public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
         DispatcherServlet dispatcherServlet = new DispatcherServlet();
         dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
         dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
         dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
         dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
         dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
         return dispatcherServlet;
      }

      @Bean
      @ConditionalOnBean(MultipartResolver.class)
      @ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
      public MultipartResolver multipartResolver(MultipartResolver resolver) {
         // Detect if the user has created a MultipartResolver but named it incorrectly
         return resolver;
      }

   }

   @Configuration(proxyBeanMethods = false)
   @Conditional(DispatcherServletRegistrationCondition.class)
   @ConditionalOnClass(ServletRegistration.class)
   @EnableConfigurationProperties(WebMvcProperties.class)
   @Import(DispatcherServletConfiguration.class)
   protected static class DispatcherServletRegistrationConfiguration {

      @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
      @ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
      public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
            WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
         DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
               webMvcProperties.getServlet().getPath());
         registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
         registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
         multipartConfig.ifAvailable(registration::setMultipartConfig);
         return registration;
      }

   }
}

• dispatcherServlet方法就是往容器中注入DispatcherServlet组件。
• dispatcherServletRegistration() 方法就是将将DispatcherServlet组件添加到Tomcat中（tomcat.addServlet()）

我们来看一下DispatcherServletRegistrationBean继承图：

image.png

在Tomcat启动的时候 会调用 ServletContextInitializer.onStartup() 方法回调，将DispatcherServlet 添加到 Tomcat中，后面的启动流程就跟SpringMVC的启动流程是一样的

2. 核心方法run()

下面是一个简单的项目，我们直接开始看run方法

@SpringBootApplication
public class SpringbootDemoApplication {
    
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(SpringbootDemoApplication.class, args);
        Object demoService = run.getBean("demoService");
        System.out.println("demoService = " + demoService);
   }
}

我们这里直接看 SpringApplication#run(java.lang.Class<?>[], java.lang.String[]) 方法:

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

我们这里先看一下 SpringApplication 的构造函数流程:

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        // 保存启动类信息
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        // 初始化环境。环境分为三种 非web环境、web环境、reactive环境三种。其判断逻辑就是判断是否存在指定的类，默认是Servlet 环境，我们这也是Servlet
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        // getSpringFactoriesInstances 方法加载了 spring.factories文件。在这里进行了首次加载spring.factoies文件。设置 ApplicationContextInitializer
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        // 获取监听器，也加载了spring.factories文件
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        // 设置启动类信息
        this.mainApplicationClass = deduceMainApplicationClass();
}

我们下面直接来看 SpringApplication#run(java.lang.String...) 方法的执行流程:

public ConfigurableApplicationContext run(String... args) {
        // 开启关于启动时间的信息监控
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        // 准备 ApplicationContext
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        //java.awt.headless是J2SE的一种模式用于在缺少显示屏、键盘或者鼠标时的系统配置，很多监控工具如jconsole 需要将该值设置为true，系统变量默认为true
        configureHeadlessProperty();
        // 1. 获取Spring的监听器类，这里是从 spring.factories 中去获取，默认的是以 org.springframework.boot.SpringApplicationRunListener 为key,获取到的监听器类型为 EventPublishingRunListener。
        SpringApplicationRunListeners listeners = getRunListeners(args);
        // 1.1 监听器发送启动事件
        listeners.starting();
        try {
                // 封装参数
                ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
                // 2. 构造容器环境。将容器的一些配置内容加载到 environment  中
                ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
                // 配置BeanInfo的忽略 ：“spring.beaninfo.ignore”，值为“true”表示跳过对BeanInfo类的搜索
                configureIgnoreBeanInfo(environment);
                // 打印信息对象
                Banner printedBanner = printBanner(environment);
                // 3. 创建上下文对象
                context = createApplicationContext();
                // 从 spring.factries 中获取错误报告的类。出错的时候会调用其方法通知
                exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                                new Class[] { ConfigurableApplicationContext.class }, context);
                // 4. 准备刷新上下文
                prepareContext(context, environment, listeners, applicationArguments, printedBanner);
                // 5. 刷新上下文
                refreshContext(context);
                // 结束刷新，留待扩展功能，并未实现什么
                afterRefresh(context, applicationArguments);
                // 停止监听
                stopWatch.stop();
                if (this.logStartupInfo) {
                        new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
                }
                // 监听器发送启动结束时间
                listeners.started(context);
                // 调用 ApplicationRunner 和 CommandLineRunner 对应的方法
                callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
                handleRunFailure(context, ex, exceptionReporters, listeners);
                throw new IllegalStateException(ex);
        }

        try {
                // 发送容器运行事件
                listeners.running(context);
        }
        catch (Throwable ex) {
                handleRunFailure(context, ex, exceptionReporters, null);
                throw new IllegalStateException(ex);
        }
        return context;
}

3. run()流程步骤详解

下面我们重点分析几个步骤

3.1 获取监听器

这一步是从 spring.factories 文件中获取监听器集合，当有事件发生时调用监听器对应事件的方法。
默认的是以 org.springframework.boot.SpringApplicationRunListener 为key,获取到的监听器类型为 EventPublishingRunListener。

SpringApplicationRunListeners listeners = getRunListeners(args);

其详细代码如下：

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

这里需要注意的是 getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args) 返回的是一个Collection 类型。也就是说明在 SpringApplicationRunListeners并非代表一个监听器，而是保存了监听器集合，在默认情况下，仅有一个 EventPublishingRunListener。在 SpringApplicationRunListeners 类中也能看到，如下：

class SpringApplicationRunListeners {

    private final Log log;

    private final List<SpringApplicationRunListener> listeners;

    SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) {
        this.log = log;
        this.listeners = new ArrayList<>(listeners);
    }
    ...
}

总结一下: Spring启动时，通过 spring.factories 文件中获取监听器集合。默认类型为 EventPublishingRunListener。在事件发生时，EventPublishingRunListener 会寻找容器中 ApplicationListener 的bean，并进行事件通知。详见Spring5源码12-监听器原理

3.2 环境变量的构造

这一步的作用就是加载一些配置文件的内容

ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);

其具体实现如下:

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
                ApplicationArguments applicationArguments) {
        // Create and configure the environment
        // 获取或者创建 environment。这里获取类型是 StandardServletEnvironment 
        ConfigurableEnvironment environment = getOrCreateEnvironment();
        // 将入参配置到环境配置中
        configureEnvironment(environment, applicationArguments.getSourceArgs());
        ConfigurationPropertySources.attach(environment);
        // 发布环境准备事件。
        listeners.environmentPrepared(environment);
        bindToSpringApplication(environment);
        if (!this.isCustomEnvironment) {
                environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
                                deduceEnvironmentClass());
        }
        ConfigurationPropertySources.attach(environment);
        return environment;
}

private Class<? extends StandardEnvironment> deduceEnvironmentClass() {
        switch (this.webApplicationType) {
        case SERVLET:
                return StandardServletEnvironment.class;
        case REACTIVE:
                return StandardReactiveWebEnvironment.class;
        default:
                return StandardEnvironment.class;
        }
}

关于 webApplicationType 的值，在 org.springframework.boot.SpringApplication#SpringApplication(org.springframework.core.io.ResourceLoader, java.lang.Class<?>...) 构造函数中进行了赋值为Servlet。所以我们这里可以知道 Environment 类型为 StandardServletEnvironment 。
在 listeners.environmentPrepared(environment); 时会发送环境准备事件，环境准备事件要通知监听器如下。对于 Springboot 的配置文件application.yml或者application.properties文件的加载实际上是通过发布环境准备事件完成的，完成这项功能的就是ConfigDataEnvironmentPostProcessor。

3.2.1 application.yml 的加载

SpringBoot在启动时，读取所有的ApplicationListener下的配置类。spring-boot工程下的spring.factories文件：

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.env.EnvironmentPostProcessorApplicationListener

当EnvironmentPostProcessorApplicationListener类接收到ApplicationEnvironmentPreparedEvent的事件时，就会调用EnvironmentPostProcessorsFactory类下的getEnvironmentPostProcessors方法来获取所有的EnvironmentPostProcessor下的配置类，并触发这些类的postProcessEnvironment方法。

public class EnvironmentPostProcessorApplicationListener implements SmartApplicationListener, Ordered {
    ...
   
        public EnvironmentPostProcessorApplicationListener() {
           this(EnvironmentPostProcessorsFactory::fromSpringFactories, new DeferredLogs());
        }

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
        }
        ...
    }

    private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
        ...
        for (EnvironmentPostProcessor postProcessor : getEnvironmentPostProcessors(application.getResourceLoader(),
                event.getBootstrapContext())) {
            postProcessor.postProcessEnvironment(environment, application);
        }
    }

    List<EnvironmentPostProcessor> getEnvironmentPostProcessors(ResourceLoader resourceLoader,
            ConfigurableBootstrapContext bootstrapContext) {
        ...
        EnvironmentPostProcessorsFactory postProcessorsFactory = this.postProcessorsFactory.apply(classLoader);
        return postProcessorsFactory.getEnvironmentPostProcessors(this.deferredLogs, bootstrapContext);
    }
}


@FunctionalInterface
public interface EnvironmentPostProcessorsFactory {

   List<EnvironmentPostProcessor> getEnvironmentPostProcessors(DeferredLogFactory logFactory,
         ConfigurableBootstrapContext bootstrapContext);

   static EnvironmentPostProcessorsFactory fromSpringFactories(ClassLoader classLoader) {
      return new ReflectionEnvironmentPostProcessorsFactory(classLoader,
            SpringFactoriesLoader.loadFactoryNames(EnvironmentPostProcessor.class, classLoader));
   }

spring.factories文件中 ：

# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor,\
org.springframework.boot.env.RandomValuePropertySourceEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\
org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor,\
org.springframework.boot.reactor.DebugAgentEnvironmentPostProcessor

EnvironmentPostProcessor

EnvironmentPostProcessor是处理程序的配置的，不同的子类实现不同的配置，有处理json配置文件的、有处理yaml配置文件的、有替换配置文件中的环境变量的。

SpringBoot 2.4.0之前的版本，处理yaml配置文件的类是ConfigFileApplicationListener类
SpringBoot 2.4.0之后的版本，处理yaml配置文件的类是ConfigDataEnvironmentPostProcessor类,我们重点看这个。

ConfigDataEnvironmentPostProcessor

SpringBoot 2.4.0之后的版本，使用ConfigDataEnvironmentPostProcessor 类来加载yaml文件中的配置。

public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProcessor, Ordered {
    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
        postProcessEnvironment(environment, application.getResourceLoader(), application.getAdditionalProfiles());
    }

    void postProcessEnvironment(ConfigurableEnvironment environment, ResourceLoader resourceLoader,
            Collection<String> additionalProfiles) {
        ...
        getConfigDataEnvironment(environment, resourceLoader, additionalProfiles).processAndApply();
        ...
    }

    ConfigDataEnvironment getConfigDataEnvironment(ConfigurableEnvironment environment, ResourceLoader resourceLoader, Collection<String> additionalProfiles) {
        return new ConfigDataEnvironment(this.logFactory, this.bootstrapContext, environment, resourceLoader, additionalProfiles, this.environmentUpdateListener);
    }
}

ConfigDataEnvironment

ConfigDataEnvironmentPostProcessor 在postProcessEnvironment方法中会实例化一个ConfigDataEnvironment对象，这个对象会加载optional:classpath:/;optional:classpath:/config/;optional:file:./;optional:file:./config/;optional:file:./config/*/路径下的yaml文件。

class ConfigDataEnvironment {
    static final String LOCATION_PROPERTY = "spring.config.location";
    static final String ADDITIONAL_LOCATION_PROPERTY = "spring.config.additional-location";
    static final String IMPORT_PROPERTY = "spring.config.import";
    
    static final ConfigDataLocation[] DEFAULT_SEARCH_LOCATIONS;
    static {
        List<ConfigDataLocation> locations = new ArrayList<>();
        locations.add(ConfigDataLocation.of("optional:classpath:/;optional:classpath:/config/"));
        locations.add(ConfigDataLocation.of("optional:file:./;optional:file:./config/;optional:file:./config/*/"));
        DEFAULT_SEARCH_LOCATIONS = locations.toArray(new ConfigDataLocation[0]);
    }

    private ConfigDataEnvironmentContributors createContributors(Binder binder) {
        ...
        contributors.addAll(getInitialImportContributors(binder));
        ...
        return createContributors(contributors);
    }

    protected ConfigDataEnvironmentContributors createContributors(
            List<ConfigDataEnvironmentContributor> contributors) {
        return new ConfigDataEnvironmentContributors(this.logFactory, this.bootstrapContext, contributors);
    }

    private List<ConfigDataEnvironmentContributor> getInitialImportContributors(Binder binder) {
        List<ConfigDataEnvironmentContributor> initialContributors = new ArrayList<>();
        addInitialImportContributors(initialContributors, bindLocations(binder, IMPORT_PROPERTY, EMPTY_LOCATIONS));
        addInitialImportContributors(initialContributors,
                bindLocations(binder, ADDITIONAL_LOCATION_PROPERTY, EMPTY_LOCATIONS));
        addInitialImportContributors(initialContributors,
                bindLocations(binder, LOCATION_PROPERTY, DEFAULT_SEARCH_LOCATIONS));
        return initialContributors;
    }
}

spring.factories文件中 ：

# ConfigData Location Resolvers
org.springframework.boot.context.config.ConfigDataLocationResolver=\
org.springframework.boot.context.config.ConfigTreeConfigDataLocationResolver,\
org.springframework.boot.context.config.StandardConfigDataLocationResolver

# ConfigData Loaders
org.springframework.boot.context.config.ConfigDataLoader=\
org.springframework.boot.context.config.ConfigTreeConfigDataLoader,\
org.springframework.boot.context.config.StandardConfigDataLoader

# PropertySource Loaders
org.springframework.boot.env.PropertySourceLoader=\
org.springframework.boot.env.PropertiesPropertySourceLoader,\
org.springframework.boot.env.YamlPropertySourceLoader

processAndApply()

请求路径为：processAndApply() -> ConfigDataEnvironment#processAndApply -> ConfigDataEnvironment#processWithoutProfiles -> ConfigDataEnvironmentContributors#withProcessedImports -> ConfigDataImporter#resolveAndLoad -> ConfigDataImporter#load -> ConfigDataLoaders#load -> StandardConfigDataLoader#load -> YamlPropertySourceLoader#load
我们直接看YamlPropertySourceLoader#load 方法：

在这里加载 application.yml文件。

EnvironmentPostProcessor

如果想处理加载的配置文件，可以在自己的java项目里添加spring.factories，然后实现EnvironmentPostProcessor类。

org.springframework.boot.env.EnvironmentPostProcessor=\
com.camellibby.springboot.component.DemoEnvironmentPostProcessor

public class DemoEnvironmentPostProcessor implements EnvironmentPostProcessor {
    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
        System.out.println("DemoEnvironmentPostProcessor is starting");
    }
}

3.3 创建上下文

这一步是创建上下文了:

context = createApplicationContext();

其详细内容如下：

public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
                + "annotation.AnnotationConfigApplicationContext";

public static final String DEFAULT_SERVLET_WEB_CONTEXT_CLASS = "org.springframework.boot."
                + "web.servlet.context.AnnotationConfigServletWebServerApplicationContext";

public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework."
                + "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";


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

// org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext.Factory#create
static class Factory implements ApplicationContextFactory {

   @Override
   public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {
      return (webApplicationType != WebApplicationType.SERVLET) ? null
            : new AnnotationConfigServletWebServerApplicationContext();
   }

}

public AnnotationConfigServletWebServerApplicationContext() {
   this.reader = new AnnotatedBeanDefinitionReader(this);
   this.scanner = new ClassPathBeanDefinitionScanner(this);
}

很明显，因为我们知道 webApplicationType 值是 servlet，所以这里创建的是 AnnotationConfigServletWebServerApplicationContext 类型的上下文
这里需要注意：AnnotationConfigServletWebServerApplicationContext 构造函数中会创建 AnnotatedBeanDefinitionReader。而在 AnnotatedBeanDefinitionReader 构造函数中会调用 AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);，该方法将一些必要Bean(如ConfigurationClassPostProcessor、AutowiredAnnotationBeanPostProcessor、CommonAnnotationBeanPostProcessor 等)注入到了容器中。

3.4 上下文准备工作

上面一步，仅仅是将上下文创建出来了，并没有对上下文进行操作。这一步开始对上下文的准备操作。

prepareContext(context, environment, listeners, applicationArguments, printedBanner);

其详细内容如下：

private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
                SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
        // 设置上下文的环境变量
        context.setEnvironment(environment);
        // 执行容器后置处理 ： 可以注册beanName策略生成器、设置资源加载器，设置转换服务等。但这里默认是没有做任何处理。目的是留给后续可以扩展
        postProcessApplicationContext(context);
        // 处理所有的初始化类的初始化方法。即 spring.factories 中key 为 org.springframework.context.ApplicationContextInitializer 指向的类，调用其 initialize 方法
        applyInitializers(context);
        // 向监听器发送容器准备事件
        listeners.contextPrepared(context);
        if (this.logStartupInfo) {
                logStartupInfo(context.getParent() == null);
                logStartupProfileInfo(context);
        }
        // Add boot specific singleton beans
        // 获取上下文中的 BeanFactory。这里的BeanFactory 实际类型是  DefaultListableBeanFactory。BeanFactory 在初始化的时候，直接在构造函数里创建为 DefaultListableBeanFactory
        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        // 注册 springApplicationArguments等一系列bean
        beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
        if (printedBanner != null) {
                beanFactory.registerSingleton("springBootBanner", printedBanner);
        }
        if (beanFactory instanceof DefaultListableBeanFactory) {
                // 设置是否允许bean定义覆盖
                ((DefaultListableBeanFactory) beanFactory)
                                .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }
        // 如果允许懒加载，则添加对应的BeanFactory后置处理器
        if (this.lazyInitialization) {
                context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
        }
        // Load the sources
        // 这里加载的实际上是启动类
        Set<Object> sources = getAllSources();
        Assert.notEmpty(sources, "Sources must not be empty");
        // 这里将启动类加入到 beanDefinitionMap 中，为后续的自动化配置做好了基础
        load(context, sources.toArray(new Object[0]));
        // 发送容器加载完成事件
        listeners.contextLoaded(context);
}

....

// 需要注意这里的 sources参数实际上是 启动类的 Class
protected void load(ApplicationContext context, Object[] sources) {
        if (logger.isDebugEnabled()) {
                logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
        }
        // 从上下文中获取 BeanDefinitionRegistry并依次创建出 BeanDefinitionLoader 。这里将sources作为参数保存到了 loader  中。也就是 loader  中保存了 启动类的Class信息
        BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources);
        if (this.beanNameGenerator != null) {
                loader.setBeanNameGenerator(this.beanNameGenerator);
        }
        if (this.resourceLoader != null) {
                loader.setResourceLoader(this.resourceLoader);
        }
        if (this.environment != null) {
                loader.setEnvironment(this.environment);
        }
        loader.load();
}

我们这里比较关键的方法是 loader.load(); 方法 其中 loader.load(); 不管怎么跳转，最后都会跳转到 BeanDefinitionLoader#load(java.lang.Class<?>) 方法中。如下:

private int load(Class<?> source) {
        // 判断是否存在 groovy 加载方式
        if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
                // Any GroovyLoaders added in beans{} DSL can contribute beans here
                GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class);
                load(loader);
        }
        // 判断 source 是否 需要被加载到Spring容器中。实际上是根据判断是否存在 @Component 
        if (isComponent(source)) {
                // 将source 就是启动类的 class，注册到 annotatedReader 中。annotatedReader  类型是AnnotatedBeanDefinitionReader。
                this.annotatedReader.register(source);
                return 1;
        }
        return 0;
}

this.annotatedReader.register(source); 后续会跳转到 AnnotatedBeanDefinitionReader#doRegisterBean 方法中，看名字就知道是这个方法的工作是 注册 Bean。实际上，在这个方法中完成了对@Qualifier 以及一些其他注解的处理。具体如下：

// 这里的 beanClass 其实就是启动类的 beanClass 
private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
                @Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
                @Nullable BeanDefinitionCustomizer[] customizers) {
        // 将Class 转换成一个 BeanDefinition 类
        AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
        // 判断是否应该跳过
        if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
                return;
        }

        abd.setInstanceSupplier(supplier);
        // 保存其作用域信息。这里默认是 singleton
        ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
        abd.setScope(scopeMetadata.getScopeName());
        // 获取 beanName
        String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
        // 处理一些通用的注解信息，包括Lazy、Primary、DependsOn、Role、Description 注解。获取其value值并保存到 abd 中
        AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
        // 处理  @Qualifier 
        if (qualifiers != null) {
                for (Class<? extends Annotation> qualifier : qualifiers) {
                        if (Primary.class == qualifier) {
                                abd.setPrimary(true);
                        }
                        else if (Lazy.class == qualifier) {
                                abd.setLazyInit(true);
                        }
                        else {
                                abd.addQualifier(new AutowireCandidateQualifier(qualifier));
                        }
                }
        }
        if (customizers != null) {
                for (BeanDefinitionCustomizer customizer : customizers) {
                        customizer.customize(abd);
                }
        }

        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
        // 判断是否需要创建代理，需要则创建
        definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
        // 将 BeanDefinitionHolder  注册到 容器中。此时的 registry 就是 AnnotationConfigServletWebServerApplicationContext。在BeanDefinitionLoader 初始化的时候保存的
        BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}

3.5 SpringApplication#refreshContext

对容器进行一个刷新工作。在此进行了大量的工作。这里的处理工作就由Springboot交给 Spring来处理了

refreshContext(context);

详细如下:

private void refreshContext(ConfigurableApplicationContext context) {
        refresh(context);
        if (this.registerShutdownHook) {
                try {
                        context.registerShutdownHook();
                }
                catch (AccessControlException ex) {
                        // Not allowed in some environments.
                }
        }
}

最终会跳转到 AbstractApplicationContext#refresh 中。而关于 AbstractApplicationContext#refresh 方法在之前的文章中有过介绍，参见Spring5源码11-容器刷新refresh方法(注解版)。我们重点看一下Tomcat的启动过程，着重看onRefresh()方法：

@Override
public void refresh() throws BeansException, IllegalStateException {

         // Initialize other special beans in specific context subclasses.
         onRefresh();

         // Check for listener beans and register them.
         registerListeners();      
}

SpringBoot使用ServletWebServerApplicationContext#onRefresh：

@Override
protected void onRefresh() {
   super.onRefresh();
   try {
      createWebServer();
   }
   catch (Throwable ex) {
      throw new ApplicationContextException("Unable to start web server", ex);
   }
}

直接看createWebServer()方法：

private void createWebServer() {
   WebServer webServer = this.webServer;
   ServletContext servletContext = getServletContext();
   if (webServer == null && servletContext == null) {
      StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");
      // 本文环境获取的是tomcatServletWebServerFactory，默认的
      ServletWebServerFactory factory = getWebServerFactory();
      createWebServer.tag("factory", factory.getClass().toString());
      this.webServer = factory.getWebServer(getSelfInitializer());
      createWebServer.end();
      getBeanFactory().registerSingleton("webServerGracefulShutdown",
            new WebServerGracefulShutdownLifecycle(this.webServer));
      getBeanFactory().registerSingleton("webServerStartStop",
            new WebServerStartStopLifecycle(this, this.webServer));
   }
   else if (servletContext != null) {
      try {
         getSelfInitializer().onStartup(servletContext);
      }
      catch (ServletException ex) {
         throw new ApplicationContextException("Cannot initialize servlet context", ex);
      }
   }
   initPropertySources();
}

3.5.1 getWebServerFactory()

如下所示，从容器中获取ServletWebServerFactory类型的bean，唯一一个，否则抛出异常。本文环境获取的是tomcatServletWebServerFactory。

protected ServletWebServerFactory getWebServerFactory() {
   // Use bean names so that we don't consider the hierarchy
   String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
   if (beanNames.length == 0) {
      throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
            + "ServletWebServerFactory bean.");
   }
   if (beanNames.length > 1) {
      throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
            + "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
   }
   return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}

3.5.2 getSelfInitializer()

ServletWebServerApplicationContext的getSelfInitializer方法，返回的是ServletContextInitializer。

private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
    return this::selfInitialize;
}

看到this::selfInitialize是不是比较迷糊？典型的java8的lambda写法。我们看一下ServletContextInitializer 可能就明白了。
如下所示，其是一个函数式接口，只有一个onStartup方法。函数式接口(有且仅有一个抽象方法的接口)可以使用lambda式的写法。

@FunctionalInterface
public interface ServletContextInitializer {
     // 初始化过程中，使用给定的servlets、filters、listeners
     //context-params and attributes necessary配置ServletContext
    void onStartup(ServletContext servletContext) throws ServletException;

}

我们这里获取到的本质是一个lambda，参数则是当前this，如下图所示：

image.png

this::selfInitialize中的selfInitialize则指的是ServletWebServerApplicationContext的selfInitialize方法。this指的是AnnotationConfigServletWebServerApplicationContext，其继承于ServletWebServerApplicationContext

private void selfInitialize(ServletContext servletContext) throws ServletException {
    prepareWebApplicationContext(servletContext);
    registerApplicationScope(servletContext);
    WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
    for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
        beans.onStartup(servletContext);
    }
}

其实换成匿名类的写法则是：

new ServletContextInitializer() {
      @Override
      public void onStartup(ServletContext servletContext) throws ServletException {
        selfInitialize(servletContext);
      }
};

3.5.3 getWebServer(）

本文这里是TomcatServletWebServerFactory#getWebServer方法。

@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
    if (this.disableMBeanRegistry) {
    // registry = new NoDescriptorRegistry();
        Registry.disableRegistry();
    }
    //实例化Tomcat
    Tomcat tomcat = new Tomcat();

    //获取临时路径 
    File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
    //设置基础路径
    tomcat.setBaseDir(baseDir.getAbsolutePath());

    //实例化Connector 并进行配置
    Connector connector = new Connector(this.protocol);
    connector.setThrowOnFailure(true);

    //这里会实例化server  service
    tomcat.getService().addConnector(connector);
    customizeConnector(connector);

    //对Connector做配置比如Protocol、URIEncoding
    tomcat.setConnector(connector);

    //这里会实例化Engine、Host
    tomcat.getHost().setAutoDeploy(false);
    configureEngine(tomcat.getEngine());
    for (Connector additionalConnector : this.additionalTomcatConnectors) {
                // todo
        tomcat.getService().addConnector(additionalConnector);
    }
    prepareContext(tomcat.getHost(), initializers);
    return getTomcatWebServer(tomcat);
}

getService

getService首先会触发getServer然后获取service。getServer如下所示会实例化Server并对其进行配置。

public Service getService() {
    return getServer().findServices()[0];
}
public Server getServer() {
   if (server != null) {
       return server;
   }
   System.setProperty("catalina.useNaming", "false");
    // 实例化 server
   server = new StandardServer();

    // 对basedir做处理
   initBaseDir();

   // Set configuration source
   ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(new File(basedir), null));
   // 为server设置port和service
   server.setPort( -1 );
   //实例化service
   Service service = new StandardService();
   service.setName("Tomcat");
   server.addService(service);
   return server;
}

prepareContext

这里会实例化TomcatEmbeddedContext并对其进行配置。

protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
    File documentRoot = getValidDocumentRoot();
    TomcatEmbeddedContext context = new TomcatEmbeddedContext();
    if (documentRoot != null) {
        context.setResources(new LoaderHidingResourceRoot(context));
    }
    context.setName(getContextPath());
    context.setDisplayName(getDisplayName());
    context.setPath(getContextPath());
    File docBase = (documentRoot != null) ? documentRoot : createTempDir("tomcat-docbase");
    context.setDocBase(docBase.getAbsolutePath());
    context.addLifecycleListener(new FixContextListener());
    context.setParentClassLoader((this.resourceLoader != null) ? this.resourceLoader.getClassLoader()
            : ClassUtils.getDefaultClassLoader());
    resetDefaultLocaleMapping(context);
    addLocaleMappings(context);
    context.setUseRelativeRedirects(false);
    try {
        context.setCreateUploadTargets(true);
    }
    catch (NoSuchMethodError ex) {
        // Tomcat is < 8.5.39. Continue.
    }
    configureTldSkipPatterns(context);
    WebappLoader loader = new WebappLoader(context.getParentClassLoader());
    loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName());
    loader.setDelegate(true);
    context.setLoader(loader);
    if (isRegisterDefaultServlet()) {
        addDefaultServlet(context);
    }
    if (shouldRegisterJspServlet()) {
        addJspServlet(context);
        addJasperInitializer(context);
    }
    context.addLifecycleListener(new StaticResourceConfigurer(context));
    ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);
    host.addChild(context);
    configureContext(context, initializersToUse);
    postProcessContext(context);
}

getTomcatWebServer

这个方法很简单，只是直接实例化了TomcatWebServer返回。其构造方法触发了initialize，这会引起后续一系列动作，包括tomcat.start()。

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
    return new TomcatWebServer(tomcat, getPort() >= 0);
}
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
    Assert.notNull(tomcat, "Tomcat Server must not be null");
    this.tomcat = tomcat;
    this.autoStart = autoStart;
        // todo
    initialize();
}

initialize()

我们回过头来，看一下initialize()方法：

private void initialize() throws WebServerException {
   logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
   synchronized (this.monitor) {
      try {
         ...
         // Start the server to trigger initialization listeners
         this.tomcat.start();

        ...
      }
   }
}

在这里将嵌入式Tomcat启动。

selfInitialize

获取到TomcatWebServer后，Tomcat启动之后就触发了selfInitialize方法。这里servletContext其实是获取了ApplicationContext的一个门面/外观–ApplicationContextCade。

// ServletWebServerApplicationContext
private void selfInitialize(ServletContext servletContext) throws ServletException {
        // todo
    prepareWebApplicationContext(servletContext);
        // todo
    registerApplicationScope(servletContext);
        // todo
    WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
        // todo
    for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
        beans.onStartup(servletContext);
    }
}

prepareWebApplicationContext
ServletWebServerApplicationContext的prepareWebApplicationContext方法如下所示，简单来讲就是为servletContext设置根容器属性并为当前应用上下文ApplicationContext设置servletContext引用。

protected void prepareWebApplicationContext(ServletContext servletContext) {
//尝试从servletContext中获取rootContext 
        Object rootContext = servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
        if (rootContext != null) {
                if (rootContext == this) {
                        throw new IllegalStateException(
                                        "Cannot initialize context because there is already a root application context present - "
                                                        + "check whether you have multiple ServletContextInitializers!");
                }
                return;
        }
        Log logger = LogFactory.getLog(ContextLoader.class);
        // 这个日志是不是很熟悉？！
        servletContext.log("Initializing Spring embedded WebApplicationContext");
        try {

//向servletContext设置属性 ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE
                servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this);
                if (logger.isDebugEnabled()) {
                        logger.debug("Published root WebApplicationContext as ServletContext attribute with name ["
                                        + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
                }
                // 为ApplicationContext设置servletContext引用
                setServletContext(servletContext);
                if (logger.isInfoEnabled()) {
                        long elapsedTime = System.currentTimeMillis() - getStartupDate();
                        logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
                }
        }
        catch (RuntimeException | Error ex) {
                logger.error("Context initialization failed", ex);
                servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
                throw ex;
        }
}

registerApplicationScope:
ServletWebServerApplicationContext的registerApplicationScope方法如下所示，简单来讲就是(扩展)注册scope-application。这里会实例化一个ServletContextScope (包装了servletContext)，然后注册到BeanFactory中并为servletContext设置属性。

private void registerApplicationScope(ServletContext servletContext) {
        ServletContextScope appScope = new ServletContextScope(servletContext);
        // application
        getBeanFactory().registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope);
        // Register as ServletContext attribute, for ContextCleanupListener to detect it.
        servletContext.setAttribute(ServletContextScope.class.getName(), appScope);
}

我们在Spring中refresh分析之postProcessBeanFactory方法详解提到了request-RequestScope，session–SessionScope的注册，本文这里注册了application-ServletContextScope注册。

registerEnvironmentBeans:
WebApplicationContextUtils的registerEnvironmentBeans方法。

public static void registerEnvironmentBeans(ConfigurableListableBeanFactory bf, @Nullable ServletContext sc) {
        registerEnvironmentBeans(bf, sc, null);
}

public static void registerEnvironmentBeans(ConfigurableListableBeanFactory bf,
                @Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) {

//将servletContext作为单例注册容器
        if (servletContext != null && !bf.containsBean(WebApplicationContext.SERVLET_CONTEXT_BEAN_NAME)) {
                bf.registerSingleton(WebApplicationContext.SERVLET_CONTEXT_BEAN_NAME, servletContext);
        }

// 将servletConfig 作为单例注册容器本文这里没有触发
        if (servletConfig != null && !bf.containsBean(ConfigurableWebApplicationContext.SERVLET_CONFIG_BEAN_NAME)) {
                bf.registerSingleton(ConfigurableWebApplicationContext.SERVLET_CONFIG_BEAN_NAME, servletConfig);
        }
// String CONTEXT_PARAMETERS_BEAN_NAME = "contextParameters";
        if (!bf.containsBean(WebApplicationContext.CONTEXT_PARAMETERS_BEAN_NAME)) {
                Map<String, String> parameterMap = new HashMap<>();
                if (servletContext != null) {
                // 获取servletContextd的初始化参数
                        Enumeration<?> paramNameEnum = servletContext.getInitParameterNames();
                        while (paramNameEnum.hasMoreElements()) {
                                String paramName = (String) paramNameEnum.nextElement();
                                parameterMap.put(paramName, servletContext.getInitParameter(paramName));
                        }
                }
                // 本文这里servletConfig 为null
                if (servletConfig != null) {
                // // 获取servletConfig的初始化参数
                        Enumeration<?> paramNameEnum = servletConfig.getInitParameterNames();
                        while (paramNameEnum.hasMoreElements()) {
                                String paramName = (String) paramNameEnum.nextElement();
                                parameterMap.put(paramName, servletConfig.getInitParameter(paramName));
                        }
                }
                // 将contextParameters作为单例注册到容器
                bf.registerSingleton(WebApplicationContext.CONTEXT_PARAMETERS_BEAN_NAME,
                                Collections.unmodifiableMap(parameterMap));
        }

// String CONTEXT_ATTRIBUTES_BEAN_NAME = "contextAttributes";
        if (!bf.containsBean(WebApplicationContext.CONTEXT_ATTRIBUTES_BEAN_NAME)) {
                Map<String, Object> attributeMap = new HashMap<>();
                if (servletContext != null) {
                        Enumeration<?> attrNameEnum = servletContext.getAttributeNames();
                        while (attrNameEnum.hasMoreElements()) {
                                String attrName = (String) attrNameEnum.nextElement();
                                attributeMap.put(attrName, servletContext.getAttribute(attrName));
                        }
                }
                // 将contextAttributes作为单例注册到容器
                bf.registerSingleton(WebApplicationContext.CONTEXT_ATTRIBUTES_BEAN_NAME,
                                Collections.unmodifiableMap(attributeMap));
        }
}

触发ServletContextInitializer的onStartup:如下所示，这里会获取ServletContextInitializer的所有实例，遍历触发其onStartup方法。

for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
        beans.onStartup(servletContext);
}

如下所示，将会挨个触发这5个的onStartup方法:

image.png

核心代码如下：

// org.springframework.boot.web.servlet.RegistrationBean#onStartup
@Override
public final void onStartup(ServletContext servletContext) throws ServletException {
   String description = getDescription();
   if (!isEnabled()) {
      logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
      return;
   }
   register(description, servletContext);
}
// org.springframework.boot.web.servlet.DynamicRegistrationBean#register
@Override
protected final void register(String description, ServletContext servletContext) {
   D registration = addRegistration(description, servletContext);
   if (registration == null) {
      logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");
      return;
   }
   configure(registration);
}
// org.springframework.boot.web.servlet.ServletRegistrationBean#addRegistration
@Override
protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) {
   String name = getServletName();
   return servletContext.addServlet(name, this.servlet);
}

在这里，会将Dispatcher加入到Tomcat中，之后就是Tomcat的启动流程，跟之前启动SpringMVC流程一样

3.6 afterRefresh

进入org.springframework.boot.SpringApplication#afterRefresh方法中

protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) {
}

这里啥也没做，就是一个模板方法，可能使用于扩展性的吧

3.7 callRunners

进入org.springframework.boot.SpringApplication#callRunners方法中

private void callRunners(ApplicationContext context, ApplicationArguments args) {
   List<Object> runners = new ArrayList<>();
   runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
   runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
   AnnotationAwareOrderComparator.sort(runners);
   for (Object runner : new LinkedHashSet<>(runners)) {
      if (runner instanceof ApplicationRunner) {
         callRunner((ApplicationRunner) runner, args);
      }
      if (runner instanceof CommandLineRunner) {
         callRunner((CommandLineRunner) runner, args);
      }
   }
}
private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
   try {
      (runner).run(args);
   }
   catch (Exception ex) {
      throw new IllegalStateException("Failed to execute ApplicationRunner", ex);
   }
}

可以看到这里主要就是从容器中获取runner对象并调用对应的run方法。

3.8 流程框图

image.png