this.localExecutor = Executors.newSingleThreadScheduledExecutor();
 this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);

public class TaskSchedulingAutoConfiguration {
   @Bean
   @ConditionalOnBean(name = TaskManagementConfigUtils.SCHEDULED_ANNOTATION_PROCESSOR_BEAN_NAME)
   @ConditionalOnMissingBean({ SchedulingConfigurer.class, TaskScheduler.class, ScheduledExecutorService.class })
   public ThreadPoolTaskScheduler taskScheduler(TaskSchedulerBuilder builder) {
     return builder.build();
   }
   
   @Bean
   @ConditionalOnMissingBean
   public TaskSchedulerBuilder taskSchedulerBuilder(TaskSchedulingProperties properties,
       ObjectProvider<TaskSchedulerCustomizer> taskSchedulerCustomizers) {
     TaskSchedulerBuilder builder = new TaskSchedulerBuilder();
     builder = builder.poolSize(properties.getPool().getSize());
     Shutdown shutdown = properties.getShutdown();
     builder = builder.awaitTermination(shutdown.isAwaitTermination());
     builder = builder.awaitTerminationPeriod(shutdown.getAwaitTerminationPeriod());
     builder = builder.threadNamePrefix(properties.getThreadNamePrefix());
     builder = builder.customizers(taskSchedulerCustomizers);
     return builder;
   }
 }

@Configuration(proxyBeanMethods = false)
 public abstract class AbstractAsyncConfiguration implements ImportAware {
   @Nullable
   protected Supplier<Executor> executor;
   @Nullable
   protected Supplier<AsyncUncaughtExceptionHandler> exceptionHandler;
   // 在容器中查找AsyncConfigurer Bean 且只能有一個
   @Autowired
   void setConfigurers(ObjectProvider<AsyncConfigurer> configurers) {
     Supplier<AsyncConfigurer> configurer = SingletonSupplier.of(() -> {
       List<AsyncConfigurer> candidates = configurers.stream().collect(Collectors.toList());
       if (CollectionUtils.isEmpty(candidates)) {
         return null;
       }
       if (candidates.size() > 1) {
         throw new IllegalStateException("Only one AsyncConfigurer may exist");
       }
       return candidates.get(0);
     });
     this.executor = adapt(configurer, AsyncConfigurer::getAsyncExecutor);
     this.exceptionHandler = adapt(configurer, AsyncConfigurer::getAsyncUncaughtExceptionHandler);
   }
 
   private <T> Supplier<T> adapt(Supplier<AsyncConfigurer> supplier, Function<AsyncConfigurer, T> provider) {
     return () -> {
       AsyncConfigurer configurer = supplier.get();
       return (configurer != null ? provider.apply(configurer) : null);
     };
   }
 }

public class AsyncAnnotationBeanPostProcessor extends AbstractBeanFactoryAwareAdvisingPostProcessor {
   @Nullable
   private Supplier<Executor> executor;
   @Nullable
   private Supplier<AsyncUncaughtExceptionHandler> exceptionHandler;
   @Override
   public void setBeanFactory(BeanFactory beanFactory) {
     super.setBeanFactory(beanFactory);
     // 構建切面Advisor
     AsyncAnnotationAdvisor advisor = new AsyncAnnotationAdvisor(this.executor, this.exceptionHandler);
     if (this.asyncAnnotationType != null) {
       advisor.setAsyncAnnotationType(this.asyncAnnotationType);
     }
     advisor.setBeanFactory(beanFactory);
     this.advisor = advisor;
   }
 }
 public class AsyncAnnotationAdvisor extends AbstractPointcutAdvisor implements BeanFactoryAware {
   public AsyncAnnotationAdvisor(
       @Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
 
     Set<Class<? extends Annotation>> asyncAnnotationTypes = new LinkedHashSet<>(2);
     asyncAnnotationTypes.add(Async.class);
     try {
       asyncAnnotationTypes.add((Class<? extends Annotation>)
           ClassUtils.forName("javax.ejb.Asynchronous", AsyncAnnotationAdvisor.class.getClassLoader()));
     }
     // 構建通知類
     this.advice = buildAdvice(executor, exceptionHandler);
     this.pointcut = buildPointcut(asyncAnnotationTypes);
   }
   protected Advice buildAdvice(
       @Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
 
     AnnotationAsyncExecutionInterceptor interceptor = new AnnotationAsyncExecutionInterceptor(null);
     // 調用父類方法
     interceptor.configure(executor, exceptionHandler);
     return interceptor;
   }
 }
 public abstract class AsyncExecutionAspectSupport implements BeanFactoryAware { 
   public void configure(@Nullable Supplier<Executor> defaultExecutor,
       @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
 
     // 如果defaultExecutor則調用getDefaultExecutor方法，該方法在子類重寫了
     this.defaultExecutor = new SingletonSupplier<>(defaultExecutor, () -> getDefaultExecutor(this.beanFactory));
     this.exceptionHandler = new SingletonSupplier<>(exceptionHandler, SimpleAsyncUncaughtExceptionHandler::new);
   }
   protected Executor getDefaultExecutor(@Nullable BeanFactory beanFactory) {
     if (beanFactory != null) {
       try {
         // 容器中查找TaskExecutor類型的Bean
         return beanFactory.getBean(TaskExecutor.class);
       } catch (NoUniqueBeanDefinitionException ex) {
         try {
           return beanFactory.getBean(DEFAULT_TASK_EXECUTOR_BEAN_NAME, Executor.class);
         } catch (NoSuchBeanDefinitionException ex2) {
         }
       } catch (NoSuchBeanDefinitionException ex) {
         try {
           return beanFactory.getBean(DEFAULT_TASK_EXECUTOR_BEAN_NAME, Executor.class);
         } catch (NoSuchBeanDefinitionException ex2) {
         }
         // Giving up -> either using local default executor or none at all...
       }
     }
     return null;
   }
 }
 public class AsyncExecutionInterceptor extends AsyncExecutionAspectSupport implements MethodInterceptor, Ordered {
   protected Executor getDefaultExecutor(@Nullable BeanFactory beanFactory) {
     // 先通過父類獲取
     Executor defaultExecutor = super.getDefaultExecutor(beanFactory);
     // 如果父類獲取不到，則創建默認的SimpleAsyncTaskExecutor
     return (defaultExecutor != null ? defaultExecutor : new SimpleAsyncTaskExecutor());
   }
 }

public class RequestMappingHandlerAdapter {
   // 默認是一個沒有上限的線程池
   private AsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor("MvcAsync");
   protected ModelAndView invokeHandlerMethod(
     HttpServletRequest request,
     HttpServletResponse response, 
     HandlerMethod handlerMethod) throws Exception {
     // ...
     WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
     asyncManager.setTaskExecutor(this.taskExecutor);
     // ...
   }
 }

public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration{}
 public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
   private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
   // WebMvcConfigurer默認實現
   @Autowired(required = false)
   public void setConfigurers(List<WebMvcConfigurer> configurers) {
     if (!CollectionUtils.isEmpty(configurers)) {
       this.configurers.addWebMvcConfigurers(configurers);
     }
   }
   @Override
   protected void configureAsyncSupport(AsyncSupportConfigurer configurer) {
     this.configurers.configureAsyncSupport(configurer);
   }
 }
 public class WebMvcConfigurationSupport implements ApplicationContextAware, ServletContextAware {
   private AsyncSupportConfigurer asyncSupportConfigurer;
   @Bean
   public RequestMappingHandlerAdapter requestMappingHandlerAdapter(...) {
     // ...
     AsyncSupportConfigurer configurer = getAsyncSupportConfigurer();
     if (configurer.getTaskExecutor() != null) {
       adapter.setTaskExecutor(configurer.getTaskExecutor());
     }
     // ...
   }
   protected AsyncSupportConfigurer getAsyncSupportConfigurer() {
     if (this.asyncSupportConfigurer == null) {
       this.asyncSupportConfigurer = new AsyncSupportConfigurer();
       configureAsyncSupport(this.asyncSupportConfigurer);
     }
     return this.asyncSupportConfigurer;
   }
 }
 public class WebMvcAutoConfiguration {
   public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ServletContextAware {
     public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
       // 判斷容器中是否有beanName = applicationTaskExecutor 的Bean
       if (this.beanFactory.containsBean(TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME)) {
         // 通過beanName = applicationTaskExecutor獲取bean對象
         Object taskExecutor = this.beanFactory.getBean(TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME);
         // 判斷是否AsyncTaskExecutor對象
         if (taskExecutor instanceof AsyncTaskExecutor) {
           configurer.setTaskExecutor(((AsyncTaskExecutor) taskExecutor));
         }
       }
       Duration timeout = this.mvcProperties.getAsync().getRequestTimeout();
       if (timeout != null) {
         configurer.setDefaultTimeout(timeout.toMillis());
       }
     }
   }
 }