Spring boot 启动过程工作原理

心已赠人 2023-07-15 09:17 17阅读 0赞

## 1. SpringBootApplication rum()方法 ##

@SpringBootApplication  //注解
    public class SpringBootTestApplication{
    
        public static void main(String[] args) {
            ConfigurableApplicationContext context  =SpringApplication.run(SpringBootStudySourceApplication.class, args);
        }
    }

## 2. SpringApplication注解 ##

/**
 * Indicates a {@link Configuration configuration} class that declares one or more
 * {@link Bean @Bean} methods and also triggers {@link EnableAutoConfiguration
 * auto-configuration} and {@link ComponentScan component scanning}. This is a convenience
 * annotation that is equivalent to declaring {@code @Configuration},
 * {@code @EnableAutoConfiguration} and {@code @ComponentScan}.
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @since 1.2.0
 */
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Inherited
 @SpringBootConfiguration
 @EnableAutoConfiguration
 @ComponentScan(excludeFilters = {//没有指定，默认是夹这个注解类所在的包
 @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
 @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
 public @interface SpringBootApplication {
 
 /**
 * Exclude specific auto-configuration classes such that they will never be applied.
 * @return the classes to exclude
 */
 @AliasFor(annotation = EnableAutoConfiguration.class)
 Class<?>[] exclude() default {};
 
 /**
 * Exclude specific auto-configuration class names such that they will never be
 * applied.
 * @return the class names to exclude
 * @since 1.3.0
 */
 @AliasFor(annotation = EnableAutoConfiguration.class)
 String[] excludeName() default {};
 
 /**
 * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses}
 * for a type-safe alternative to String-based package names.
 * @return base packages to scan
 * @since 1.3.0
 */
 @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
 String[] scanBasePackages() default {};
 
 /**
 * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to
 * scan for annotated components. The package of each class specified will be scanned.
 * 
 * Consider creating a special no-op marker class or interface in each package that
 * serves no purpose other than being referenced by this attribute.
 * @return base packages to scan
 * @since 1.3.0
 */
 @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
 Class<?>[] scanBasePackageClasses() default {};
 
 }
 
 @EnableAutoConfiguration  @ComponentScan @configuration  三个注解的复合

## 3. SpringApplication构造方法 ##

/**
 * 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) {
        //开始计时
 StopWatch stopWatch = new StopWatch();
 stopWatch.start();
 ConfigurableApplicationContext context = null;
 Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        //设置系统属性java.awt.handless 
 configureHeadlessProperty();
        //获取到META-INF/spring.factories中的配置SpringApplicationRunListeners
 SpringApplicationRunListeners listeners = getRunListeners(args);
        //循环执行
 listeners.starting();
 try {
            //命令行为参数，包装了ApplicationArguments
 ApplicationArguments applicationArguments = new DefaultApplicationArguments(
 args);
            //主备好environment
 ConfigurableEnvironment environment = prepareEnvironment(listeners,
 applicationArguments);
            //
 configureIgnoreBeanInfo(environment);
            //打印图标
 Banner printedBanner = printBanner(environment);
            //创建applicationContext
 context = createApplicationContext();
            //获取到META-INF/spring.factories中的配置SpringBootExceptionReporter
 exceptionReporters = getSpringFactoriesInstances(
 SpringBootExceptionReporter.class,
 new Class[] { ConfigurableApplicationContext.class }, context);
            //准备ApplicationContext
 prepareContext(context, environment, listeners, applicationArguments,
 printedBanner);
            //刷新ApplicationContext
 refreshContext(context);
 afterRefresh(context, applicationArguments);
 stopWatch.stop();
 if (this.logStartupInfo) {
 new StartupInfoLogger(this.mainApplicationClass)
 .logStarted(getApplicationLog(), stopWatch);
 }
            //发布started事件
 listeners.started(context);
            //执行所有的runners
 callRunners(context, applicationArguments);
              /**
            runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
    runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
            **/
 }
 catch (Throwable ex) {
 handleRunFailure(context, ex, exceptionReporters, listeners);
 throw new IllegalStateException(ex);
 }
 
 try {
            //发布所有running事件
 listeners.running(context);
          
 }
 catch (Throwable ex) {
 handleRunFailure(context, ex, exceptionReporters, null);
 throw new IllegalStateException(ex);
 }
        //返回
 return context;
 }

## 4. 环境准备过程 ##

private ConfigurableEnvironment prepareEnvironment(
                SpringApplicationRunListeners listeners,
                ApplicationArguments applicationArguments) {
            // Create and configure the environment
            //系统环境变量、系统参数、具体应用类配置参数
            ConfigurableEnvironment environment = getOrCreateEnvironment();
            //环境配置 
            /**configurePropertySources(environment, args);
            configureProfiles(environment, args);
            **/
            configureEnvironment(environment, applicationArguments.getSourceArgs());
            //触发RunListener环境准备回调
            listeners.environmentPrepared(environment);
            //绑定springApplication
            bindToSpringApplication(environment);
            if (!this.isCustomEnvironment) {
                environment = new EnvironmentConverter(getClassLoader())
                        .convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
            }
            ConfigurationPropertySources.attach(environment);
            return environment;
        }

## 5. 参数的配置是在哪加载的 ##

/**
 * Configure which profiles are active (or active by default) for this application
 * environment. Additional profiles may be activated during configuration file
 * processing via the {@code spring.profiles.active} property.
 * @param environment this application's environment
 * @param args arguments passed to the {@code run} method
 * @see #configureEnvironment(ConfigurableEnvironment, String[])
 * @see org.springframework.boot.context.config.ConfigFileApplicationListener
 */
 protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
 environment.getActiveProfiles(); // ensure they are initialized
 // But these ones should go first (last wins in a property key clash)
 Set<String> profiles = new LinkedHashSet<>(this.additionalProfiles);
 profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
 environment.setActiveProfiles(StringUtils.toStringArray(profiles));
 }

ConfigFileApplicationListener

//实现了EnvironmentPostProcessor ，在这里加载配置文件
 public class ConfigFileApplicationListener
 implements EnvironmentPostProcessor, SmartApplicationListener, Ordered {
 
 //    
 @Override
 public void postProcessEnvironment(ConfigurableEnvironment environment,
 SpringApplication application) {
 addPropertySources(environment, application.getResourceLoader());
 }
    
    //实现了ApplicationListener
   @Override
 public void onApplicationEvent(ApplicationEvent event) {
 if (event instanceof ApplicationEnvironmentPreparedEvent) {
 onApplicationEnvironmentPreparedEvent(
 (ApplicationEnvironmentPreparedEvent) event);
 }
 if (event instanceof ApplicationPreparedEvent) {
 onApplicationPreparedEvent(event);
 }
 }
    
    
   private void onApplicationEnvironmentPreparedEvent(
 ApplicationEnvironmentPreparedEvent event) {
 List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
 postProcessors.add(this);
 AnnotationAwareOrderComparator.sort(postProcessors);
 for (EnvironmentPostProcessor postProcessor : postProcessors) {
 postProcessor.postProcessEnvironment(event.getEnvironment(),
 event.getSpringApplication());
 }
 }
    
    /**
 * Post-process the given {@code environment}.
 * @param environment the environment to post-process
 * @param application the application to which the environment belongs
 */
 void postProcessEnvironment(ConfigurableEnvironment environment,
 SpringApplication application);
 
 }

栈执行链:

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## 6. ConfigurableApplicationContext ##

### 创建准备过程 ###

/**
 * Strategy method used to create the {@link ApplicationContext}. By default this
 * method will respect any explicitly set application context or application context
 * class before falling back to a suitable default.
 * @return the application context (not yet refreshed)
 * @see #setApplicationContextClass(Class)
 */
 protected ConfigurableApplicationContext createApplicationContext() {
 // 逻辑：如果没有编程式指定contextClass，webApplicationType来选择对应默认ApplicationContext实现类
 Class<?> contextClass = this.applicationContextClass;
 if (contextClass == null) {
 try {
 switch (this.webApplicationType) {
 case SERVLET:
 contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
 break;
 case REACTIVE:
 contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
 break;
 default:
 contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
 }
 }
 catch (ClassNotFoundException ex) {
 throw new IllegalStateException(
 "Unable create a default ApplicationContext, "
 + "please specify an ApplicationContextClass",
 ex);
 }
 }
 return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
 }
 
 //默认的三个常量名包含了什么？怎么执行的？
 /**
 * The class name of application context that will be used by default for non-web
 * environments.
 */
 public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
 + "annotation.AnnotationConfigApplicationContext";
 
 /**
 * The class name of application context that will be used by default for web
 * environments.
 */
 public static final String DEFAULT_SERVLET_WEB_CONTEXT_CLASS = "org.springframework.boot."
 + "web.servlet.context.AnnotationConfigServletWebServerApplicationContext";
 
 /**
 * The class name of application context that will be used by default for reactive web
 * environments.
 */
 public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework."
 + "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";

### 加载过程 ###

private void prepareContext(ConfigurableApplicationContext context,
 ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
 ApplicationArguments applicationArguments, Banner printedBanner) {
 //设置环境对象
 context.setEnvironment(environment);
 //设置beanNameGenerator resourceLoader addConversionService
 postProcessApplicationContext(context);
    //3、应用初始化器对ApplicationContext进行初始化处理（Initializers在构造SpringApplication时就从spring.factories中加载到了）
 applyInitializers(context);
    //发布事件
    /**
    @Override
 public void contextPrepared(ConfigurableApplicationContext context) {
 this.initialMulticaster.multicastEvent(new ApplicationContextInitializedEvent(
 this.application, this.args, context));
 }
    **/
 listeners.contextPrepared(context);
    //打印startup日志信息
 if (this.logStartupInfo) {
 logStartupInfo(context.getParent() == null);
 logStartupProfileInfo(context);
 }
 // Add boot specific singleton beans 单例bean注入工厂
 ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
 beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
 if (printedBanner != null) {
 beanFactory.registerSingleton("springBootBanner", printedBanner);
 }
 if (beanFactory instanceof DefaultListableBeanFactory) {
 ((DefaultListableBeanFactory) beanFactory)
 .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
 }
 // Load the sources 加载PrimarySource、其他编程式指定的source 配置类中的Bean定
 Set<Object> sources = getAllSources();
 Assert.notEmpty(sources, "Sources must not be empty");
 load(context, sources.toArray(new Object[0]));
          //发布applictionContext加载bean定义完毕事件
 listeners.contextLoaded(context);
 }

### 刷新事件 ###

private void refreshContext(ConfigurableApplicationContext context) {
            refresh(context);
            if (this.registerShutdownHook) {
                try {
                    context.registerShutdownHook();
                }
                catch (AccessControlException ex) {
                    // Not allowed in some environments.
                }
            }
        }
        
        /**
         * Refresh the underlying {@link ApplicationContext}.
         * @param applicationContext the application context to refresh
         */
        protected void refresh(ApplicationContext applicationContext) {
            Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
            ((AbstractApplicationContext) applicationContext).refresh();
        }

### bean是在哪加载的 ###

/**
 * Create a new {@link SpringApplication} instance. The application context will load
 * beans from the specified primary sources (see {@link SpringApplication class-level}
 * documentation for details. The instance can be customized before calling
 * {@link #run(String...)}.
 * @param resourceLoader the resource loader to use
 * @param primarySources the primary bean sources
 * @see #run(Class, String[])
 * @see #setSources(Set)
 */
 @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));
 this.webApplicationType = WebApplicationType.deduceFromClasspath();
 //初始化bean定义
 setInitializers((Collection) getSpringFactoriesInstances(
 ApplicationContextInitializer.class));
 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
 this.mainApplicationClass = deduceMainApplicationClass();
 }
 
 //
 
 private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
 return getSpringFactoriesInstances(type, new Class<?>[] {});
 }
 
 private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
 Class<?>[] parameterTypes, Object... args) {
 ClassLoader classLoader = getClassLoader();
 // Use names and ensure unique to protect against duplicates
 Set<String> names = new LinkedHashSet<>(
 SpringFactoriesLoader.loadFactoryNames(type, classLoader));
 List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
 classLoader, args, names);
 AnnotationAwareOrderComparator.sort(instances);
 return instances;
 }
 
 
 //# Auto Configure
 //org.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\

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`/* * Copyright 2012-2017 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *     http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.boot.autoconfigure; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Inherited; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; import org.springframework.boot.autoconfigure.condition.ConditionalOnBean; import org.springframework.boot.autoconfigure.condition.ConditionalOnClass; import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean; import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory; import org.springframework.boot.web.servlet.server.ServletWebServerFactory; import org.springframework.context.annotation.Conditional; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; import org.springframework.core.io.support.SpringFactoriesLoader; /** * Enable auto-configuration of the Spring Application Context, attempting to guess and * configure beans that you are likely to need. Auto-configuration classes are usually * applied based on your classpath and what beans you have defined. For example, if you * have {@code tomcat-embedded.jar} on your classpath you are likely to want a * {@link TomcatServletWebServerFactory} (unless you have defined your own * {@link ServletWebServerFactory} bean). * * When using {@link SpringBootApplication}, the auto-configuration of the context is * automatically enabled and adding this annotation has therefore no additional effect. * * Auto-configuration tries to be as intelligent as possible and will back-away as you * define more of your own configuration. You can always manually {@link #exclude()} any * configuration that you never want to apply (use {@link #excludeName()} if you don't * have access to them). You can also exclude them via the * {@code spring.autoconfigure.exclude} property. Auto-configuration is always applied * after user-defined beans have been registered. * * The package of the class that is annotated with {@code @EnableAutoConfiguration}, * usually via {@code @SpringBootApplication}, has specific significance and is often used * as a 'default'. For example, it will be used when scanning for {@code @Entity} classes. * It is generally recommended that you place {@code @EnableAutoConfiguration} (if you're * not using {@code @SpringBootApplication}) in a root package so that all sub-packages * and classes can be searched. * * Auto-configuration classes are regular Spring {@link Configuration} beans. They are * located using the {@link SpringFactoriesLoader} mechanism (keyed against this class). * Generally auto-configuration beans are {@link Conditional @Conditional} beans (most * often using {@link ConditionalOnClass @ConditionalOnClass} and * {@link ConditionalOnMissingBean @ConditionalOnMissingBean} annotations). * * @author Phillip Webb * @author Stephane Nicoll * @see ConditionalOnBean * @see ConditionalOnMissingBean * @see ConditionalOnClass * @see AutoConfigureAfter * @see SpringBootApplication */ @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import(AutoConfigurationImportSelector.class)//最终执行的类 public @interface EnableAutoConfiguration { String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration"; /** * Exclude specific auto-configuration classes such that they will never be applied. * @return the classes to exclude */ Class<?>[] exclude() default {}; /** * Exclude specific auto-configuration class names such that they will never be * applied. * @return the class names to exclude * @since 1.3.0 */ String[] excludeName() default {}; } //AutoConfigurationImportSelector实现了DeferredImportSelector //所谓延迟：在所有指定的、包扫描到的@Configuration类中的bean定义注册后，才会来处理延迟导入的 /** * A variation of {@link ImportSelector} that runs after all {@code @Configuration} beans * have been processed. This type of selector can be particularly useful when the selected * imports are {@code @Conditional}. * * Implementations can also extend the {@link org.springframework.core.Ordered} * interface or use the {@link org.springframework.core.annotation.Order} annotation to * indicate a precedence against other {@link DeferredImportSelector DeferredImportSelectors}. * * Implementations may also provide an {@link #getImportGroup() import group} which * can provide additional sorting and filtering logic across different selectors. * * @author Phillip Webb * @author Stephane Nicoll * @since 4.0 */ public interface DeferredImportSelector extends ImportSelector {     } 为什么要延迟导入的方式？    让我们自己编程配置的bean提前注册，这样自动配置时的条件判断能发现到我们配置的，就能做到不再配置 自动配置的bean等。比如：如果我们自己配置了数据源bean，则使用我们配置的数据源，不在自动配置数据源。数 据源自动配置的代码中可以看到@ConditionalOnMissingBean({ DataSource.class, XADataSource.class })：     @Configuration @Conditional(PooledDataSourceCondition.class) @ConditionalOnMissingBean({ DataSource.class, XADataSource.class }) @Import({ DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class, DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class, DataSourceJmxConfiguration.class }) protected static class PooledDataSourceConfiguration { }`

### callRunners ###

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);
 }
 }
 
 private void callRunner(CommandLineRunner runner, ApplicationArguments args) {
 try {
 (runner).run(args.getSourceArgs());
 }
 catch (Exception ex) {
 throw new IllegalStateException("Failed to execute CommandLineRunner", ex);
 }
 }
 
 ApplicationRunner，CommandLineRunner 有何作用？
    
    
 @SpringBootApplication
 public class SpringBootTestApplication implements ApplicationRunner {
  
   public static void main(String[] args) {
     SpringApplication.run(SpringBootTestApplication.class, args);
  }
   @Override
   public void run(ApplicationArguments args) throws Exception {
     System.out.println("***************** " + mybean);
  }
 }
 
 
 @SpringBootApplication
 public class SpringBootTestApplication implements ApplicationRunner {
   public static void main(String[] args) {
     ConfigurableApplicationContext context =
       SpringApplication.run(SpringBootTestApplication.class, args);
     MyBean mybean = context.getBean(MyBean.class);
     mybean.doService();
  }
 }

## 7. tomcat如何跑起来 ##

context = createApplicationContext();
 
 /**
 * Strategy method used to create the {@link ApplicationContext}. By default this
 * method will respect any explicitly set application context or application context
 * class before falling back to a suitable default.
 * @return the application context (not yet refreshed)
 * @see #setApplicationContextClass(Class)
 */
 protected ConfigurableApplicationContext createApplicationContext() {
 Class<?> contextClass = this.applicationContextClass;
 if (contextClass == null) {
 try {
 switch (this.webApplicationType) {
 case SERVLET:
 contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
 break;
 case REACTIVE:
 contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
 break;
 default:
 contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
 }
 }
 catch (ClassNotFoundException ex) {
 throw new IllegalStateException(
 "Unable create a default ApplicationContext, "
 + "please specify an ApplicationContextClass",
 ex);
 }
 }
 return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
 }
 
 /**
 * The class name of application context that will be used by default for web
 * environments.
 */
 public static final String DEFAULT_SERVLET_WEB_CONTEXT_CLASS = "org.springframework.boot."
 + "web.servlet.context.AnnotationConfigServletWebServerApplicationContext";
 
 
 
 /**
 * {@link ServletWebServerApplicationContext} that accepts annotated classes as input - in
 * particular {@link org.springframework.context.annotation.Configuration @Configuration}
 * -annotated classes, but also plain {@link Component @Component} classes and JSR-330
 * compliant classes using {@code javax.inject} annotations. Allows for registering
 * classes one by one (specifying class names as config location) as well as for classpath
 * scanning (specifying base packages as config location).
 * 
 * Note: In case of multiple {@code @Configuration} classes, later {@code @Bean}
 * definitions will override ones defined in earlier loaded files. This can be leveraged
 * to deliberately override certain bean definitions via an extra Configuration class.
 *
 * @author Phillip Webb
 * @see #register(Class...)
 * @see #scan(String...)
 * @see ServletWebServerApplicationContext
 * @see AnnotationConfigWebApplicationContext
 */
 public class AnnotationConfigServletWebServerApplicationContext
 extends ServletWebServerApplicationContext implements AnnotationConfigRegistry {
    
 }
 
 //父类
 /**
 * A {@link WebApplicationContext} that can be used to bootstrap itself from a contained
 * {@link ServletWebServerFactory} bean.
 * 
 * This context will create, initialize and run an {@link WebServer} by searching for a
 * single {@link ServletWebServerFactory} bean within the {@link ApplicationContext}
 * itself. The {@link ServletWebServerFactory} is free to use standard Spring concepts
 * (such as dependency injection, lifecycle callbacks and property placeholder variables).
 * 
 * In addition, any {@link Servlet} or {@link Filter} beans defined in the context will be
 * automatically registered with the web server. In the case of a single Servlet bean, the
 * '/' mapping will be used. If multiple Servlet beans are found then the lowercase bean
 * name will be used as a mapping prefix. Any Servlet named 'dispatcherServlet' will
 * always be mapped to '/'. Filter beans will be mapped to all URLs ('/*').
 * 
 * For more advanced configuration, the context can instead define beans that implement
 * the {@link ServletContextInitializer} interface (most often
 * {@link ServletRegistrationBean}s and/or {@link FilterRegistrationBean}s). To prevent
 * double registration, the use of {@link ServletContextInitializer} beans will disable
 * automatic Servlet and Filter bean registration.
 * 
    这个context会通过从自身查找一个ServletWebServerFactory单例bean来创建、初始化、运行一个WebServer
  
 此外，在context中定义的Servlet、Filter bean会被自动注册到Web Server。如果只有一个Servlet bean，则
 会将它映射到'/' 请求地址；多个Servlet bean时，则bean name 的小写将作为 mapping 前缀；bean名
 为'dispatcherServlet' 的Servlet将映射到 '/'。Filter beans将会映射到'/*'（所有url)
 
 更高级的配置ServletContext的方式：定义实现ServletContextInitializer接口的bean，更常用的方式是通过
 配置ServletRegistrationBean和FilterRegistrationBean的方式来配Servlet、Filter.
 为防止重复注册，当使用ServletContextInitializer beans 时会关闭自动Servlet和Filter Bean注册。
 
 * Although this context can be used directly, most developers should consider using the
 * {@link AnnotationConfigServletWebServerApplicationContext} or
 * {@link XmlServletWebServerApplicationContext} variants.
 *
 * @author Phillip Webb
 * @author Dave Syer
 * @see AnnotationConfigServletWebServerApplicationContext
 * @see XmlServletWebServerApplicationContext
 * @see ServletWebServerFactory
 */
 public class ServletWebServerApplicationContext extends GenericWebApplicationContext
 implements ConfigurableWebServerApplicationContext {
 
 private static final Log logger = LogFactory
 .getLog(ServletWebServerApplicationContext.class);
 
 /**
 * Constant value for the DispatcherServlet bean name. A Servlet bean with this name
 * is deemed to be the "main" servlet and is automatically given a mapping of "/" by
 * default. To change the default behavior you can use a
 * {@link ServletRegistrationBean} or a different bean name.
 */
 public static final String DISPATCHER_SERVLET_NAME = "dispatcherServlet";
 
 private volatile WebServer webServer;
 
 private ServletConfig servletConfig;
 
 private String serverNamespace;
 
 /**
 * Create a new {@link ServletWebServerApplicationContext}.
 */
 public ServletWebServerApplicationContext() {
 }
 
 /**
 * Create a new {@link ServletWebServerApplicationContext} with the given
 * {@code DefaultListableBeanFactory}.
 * @param beanFactory the DefaultListableBeanFactory instance to use for this context
 */
 public ServletWebServerApplicationContext(DefaultListableBeanFactory beanFactory) {
 super(beanFactory);
 }
 
 /**
 * Register ServletContextAwareProcessor.
 * @see ServletContextAwareProcessor
 */
 @Override
 protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
 beanFactory.addBeanPostProcessor(
 new WebApplicationContextServletContextAwareProcessor(this));
 beanFactory.ignoreDependencyInterface(ServletContextAware.class);
 registerWebApplicationScopes();
 }
 
    //子类实现模板方法
 @Override
 public final void refresh() throws BeansException, IllegalStateException {
 try {
 super.refresh();
 }
 catch (RuntimeException ex) {
 stopAndReleaseWebServer();
 throw ex;
 }
 }
    
    //子类实现模板方法
 @Override
 protected void onRefresh() {
 super.onRefresh();
 try {
            //创建容器
 createWebServer();
 }
 catch (Throwable ex) {
 throw new ApplicationContextException("Unable to start web server", ex);
 }
 }
 
 @Override
 protected void finishRefresh() {
 super.finishRefresh();
        //webServer创建过程
 WebServer webServer = startWebServer();
 if (webServer != null) {
 publishEvent(new ServletWebServerInitializedEvent(webServer, this));
 }
 }
 
 @Override
 protected void onClose() {
 super.onClose();
 stopAndReleaseWebServer();
 }
 
    
 private void createWebServer() {
 WebServer webServer = this.webServer;
 ServletContext servletContext = getServletContext();
 if (webServer == null && servletContext == null) {
 ServletWebServerFactory factory = getWebServerFactory();
            //-----implements TomcatServletWebServerFactory---
 this.webServer = factory.getWebServer(getSelfInitializer());
 }
 else if (servletContext != null) {
 try {
 getSelfInitializer().onStartup(servletContext);
 }
 catch (ServletException ex) {
 throw new ApplicationContextException("Cannot initialize servlet context",
 ex);
 }
 }
 initPropertySources();
 }
 
 /**
 从容器中找ServletWebServerFactory类型的Bean，只能有一个。
 * Returns the {@link ServletWebServerFactory} that should be used to create the
 * embedded {@link WebServer}. By default this method searches for a suitable bean in
 * the context itself.
 * @return a {@link ServletWebServerFactory} (never {@code null})
 */
 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);
 }
 }
 
 //ServletWebServerFactory
    /**
 Factory interface that can be used to create a {@link WebServer}.
 @author Phillip Webb
 @see WebServer
 @since 2.0.0
 */
 @FunctionalInterface
 public interface ServletWebServerFactory {
   /**
   获得一个完全配置但暂停的新WebServer实例，当ApplicationContext完成refresh后再调用
   WebServer.start(),客户端才可以进行连接。
   @param initializers {@link ServletContextInitializer}s that should be applied as
   the server starts
   @return a fully configured and started {@link WebServer}
   @see WebServer#stop()
   */
   WebServer getWebServer(ServletContextInitializer... initializers);
 }
 
 /**
 * {@link AbstractServletWebServerFactory} that can be used to create
 * {@link TomcatWebServer}s. Can be initialized using Spring's
 * {@link ServletContextInitializer}s or Tomcat {@link LifecycleListener}s.
 * 
 * Unless explicitly configured otherwise this factory will create containers that listen
 * for HTTP requests on port 8080.
 *
 * @author Phillip Webb
 * @author Dave Syer
 * @author Brock Mills
 * @author Stephane Nicoll
 * @author Andy Wilkinson
 * @author Eddú Meléndez
 * @author Christoffer Sawicki
 * @since 2.0.0
 * @see #setPort(int)
 * @see #setContextLifecycleListeners(Collection)
 * @see TomcatWebServer
 */
 public class TomcatServletWebServerFactory extends AbstractServletWebServerFactory
 implements ConfigurableTomcatWebServerFactory, ResourceLoaderAware {
 
 @Override
 public WebServer getWebServer(ServletContextInitializer... initializers) {
 Tomcat tomcat = new Tomcat();
 File baseDir = (this.baseDirectory != null) ? this.baseDirectory
 : createTempDir("tomcat");
 tomcat.setBaseDir(baseDir.getAbsolutePath());
 Connector connector = new Connector(this.protocol);
 tomcat.getService().addConnector(connector);
 customizeConnector(connector);
 tomcat.setConnector(connector);
 tomcat.getHost().setAutoDeploy(false);
 configureEngine(tomcat.getEngine());
 for (Connector additionalConnector : this.additionalTomcatConnectors) {
 tomcat.getService().addConnector(additionalConnector);
 }
 prepareContext(tomcat.getHost(), initializers);
 return getTomcatWebServer(tomcat);
 }
 }

### TomcatServletWebServerFactory这个Bean哪里配置的 ###

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## ##

/**
 * {@link EnableAutoConfiguration Auto-configuration} for servlet web servers.
 *
 * @author Phillip Webb
 * @author Dave Syer
 * @author Ivan Sopov
 * @author Brian Clozel
 * @author Stephane Nicoll
 */
 @Configuration
 @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 {
 
 @Bean
 public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
 ServerProperties serverProperties) {
 return new ServletWebServerFactoryCustomizer(serverProperties);
 }
 
 @Bean
 @ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
 public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
 ServerProperties serverProperties) {
 return new TomcatServletWebServerFactoryCustomizer(serverProperties);
 }
 }
 
 
 //-------------------------EmbeddedTomcat ---------------------------
 
 /**
 * Configuration classes for servlet web servers
 * 
 * Those should be {@code @Import} in a regular auto-configuration class to guarantee
 * their order of execution.
 *
 * @author Phillip Webb
 * @author Dave Syer
 * @author Ivan Sopov
 * @author Brian Clozel
 * @author Stephane Nicoll
 */
 @Configuration
 class ServletWebServerFactoryConfiguration {
 
 @Configuration
 @ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
 @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
 public static class EmbeddedTomcat {
 
        //注入tomcatbean
 @Bean
 public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
 return new TomcatServletWebServerFactory();
 }
 
 }
 
 /**
 * Nested configuration if Jetty is being used.
 */
 @Configuration
 @ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
 WebAppContext.class })
 @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
 public static class EmbeddedJetty {
 
 @Bean
 public JettyServletWebServerFactory JettyServletWebServerFactory() {
 return new JettyServletWebServerFactory();
 }
 
 }
 
 /**
 * Nested configuration if Undertow is being used.
 */
 @Configuration
 @ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
 @ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
 public static class EmbeddedUndertow {
 
 @Bean
 public UndertowServletWebServerFactory undertowServletWebServerFactory() {
 return new UndertowServletWebServerFactory();
 }
 
 }
 }
 
 
 //-----------------------参数的解读------------
 
 /**
 * {@link ConfigurationProperties} for a web server (e.g. port and path settings).
 *
 * @author Dave Syer
 * @author Stephane Nicoll
 * @author Andy Wilkinson
 * @author Ivan Sopov
 * @author Marcos Barbero
 * @author Eddú Meléndez
 * @author Quinten De Swaef
 * @author Venil Noronha
 * @author Aurélien Leboulanger
 * @author Brian Clozel
 * @author Olivier Lamy
 * @author Chentao Qu
 */
 @ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
 public class ServerProperties {
    
 }

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