server:
  # 設置關閉方式為優(yōu)雅關閉
  shutdown: graceful
spring:
  lifecycle:
    # 優(yōu)雅關閉超時時間, 默認30s
    timeout-per-shutdown-phase: 30s

public static void main(String[] args) {
        Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("執(zhí)行 ShutdownHook ...");
            }
        }));
    }

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

@Override
public void registerShutdownHook() {
   if (this.shutdownHook == null) {
      // No shutdown hook registered yet.
      this.shutdownHook = new Thread(SHUTDOWN_HOOK_THREAD_NAME) {
         @Override
         public void run() {
            synchronized (startupShutdownMonitor) {
               // 回調(diào)去關閉容器
               doClose();
            }
         }
      };
      // 注冊鉤子
      Runtime.getRuntime().addShutdownHook(this.shutdownHook);
   }
}

private void createWebServer() {
      // 省略其他無關代碼
      this.webServer = factory.getWebServer(getSelfInitializer());
      // 注冊webServerGracefulShutdown用來實現(xiàn)server優(yōu)雅關閉
      getBeanFactory().registerSingleton("webServerGracefulShutdown",new WebServerGracefulShutdownLifecycle(this.webServer));
      // 省略其他無關代碼
}

class WebServerGracefulShutdownLifecycle implements SmartLifecycle {
   @Override
   public void stop(Runnable callback) {
      this.running = false;
      // 優(yōu)雅關閉server
      this.webServer.shutDownGracefully((result) -> callback.run());
   }
}

public class TomcatWebServer implements WebServer {
   public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {
      this.tomcat = tomcat;
      this.autoStart = autoStart;
      // 如果SpringBoot開啟了優(yōu)雅停機配置，shutdown = Shutdown.GRACEFUL
      this.gracefulShutdown = (shutdown == Shutdown.GRACEFUL) ? new GracefulShutdown(tomcat) : null;
      initialize();
   }
   @Override
   public void shutDownGracefully(GracefulShutdownCallback callback) {
      if (this.gracefulShutdown == null) {
         // 如果沒有開啟優(yōu)雅停機，會立即關閉tomcat服務器
         callback.shutdownComplete(GracefulShutdownResult.IMMEDIATE);
         return;
      }
      // 優(yōu)雅關閉服務器
      this.gracefulShutdown.shutDownGracefully(callback);
   }
}

protected void doClose() {
   if (this.active.get() && this.closed.compareAndSet(false, true)) {
      LiveBeansView.unregisterApplicationContext(this);
      // 發(fā)布 ContextClosedEvent 事件
      publishEvent(new ContextClosedEvent(this));
      // 回調(diào)所有實現(xiàn)Lifecycle 接口的Bean的stop方法
      if (this.lifecycleProcessor != null) {
            this.lifecycleProcessor.onClose();
      }
      // 銷毀bean, 關閉容器
      destroyBeans();
      closeBeanFactory();
      onClose();
      if (this.earlyApplicationListeners != null) {
         this.applicationListeners.clear();
         this.applicationListeners.addAll(this.earlyApplicationListeners);
      }
      // Switch to inactive.
      this.active.set(false);
   }
}

public class DefaultLifecycleProcessor implements LifecycleProcessor, BeanFactoryAware {
   @Override
   public void onClose() {
      stopBeans();
      this.running = false;
   }
   private void stopBeans() {
      //獲取所有的 Lifecycle bean
      Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
      //按Phase值對bean分組, 如果沒有實現(xiàn) Phased 接口則認為 Phase 是 0
      Map<Integer, LifecycleGroup> phases = new HashMap<>();
      lifecycleBeans.forEach((beanName, bean) -> {
         int shutdownPhase = getPhase(bean);
         LifecycleGroup group = phases.get(shutdownPhase);
         if (group == null) {
            group = new LifecycleGroup(shutdownPhase, this.timeoutPerShutdownPhase, lifecycleBeans, false);
            phases.put(shutdownPhase, group);
         }
         group.add(beanName, bean);
      });
      if (!phases.isEmpty()) {
         List<Integer> keys = new ArrayList<>(phases.keySet());
         //按照 Phase 值倒序
         keys.sort(Collections.reverseOrder());
         // Phase值越大優(yōu)先級越高，先執(zhí)行
         for (Integer key : keys) {
            phases.get(key).stop();
         }
      }
   }

// DefaultLifecycleProcessor內(nèi)部類
private class LifecycleGroup {
   public void stop() {
      this.members.sort(Collections.reverseOrder());
      // count值默認為該組smartLifeCycel bean的數(shù)量
      CountDownLatch latch = new CountDownLatch(this.smartMemberCount);
      // 用于日志打印，打印等待超時未關閉成功的beanName
      Set<String> countDownBeanNames = Collections.synchronizedSet(new LinkedHashSet<>());
      Set<String> lifecycleBeanNames = new HashSet<>(this.lifecycleBeans.keySet());
      for (LifecycleGroupMember member : this.members) {
         if (lifecycleBeanNames.contains(member.name)) {
            // bean如果還沒關閉,執(zhí)行關閉方法
            doStop(this.lifecycleBeans, member.name, latch, countDownBeanNames);
         }
         else if (member.bean instanceof SmartLifecycle) {
            // 如果是SmartLifecycle bean 并且已經(jīng)被提前處理了(依賴其他更優(yōu)先關閉的bean,會提前關閉)
            latch.countDown();
         }
      }
      try {
         // 等待該組 所有smartLifeCycel bean成功關閉 或者 超時
         // 等待時間默認30s， 如果沒有配置timeout-per-shutdown-phase
         latch.await(this.timeout, TimeUnit.MILLISECONDS);
      }
      catch (InterruptedException ex) {
         Thread.currentThread().interrupt();
      }
   }
}
private void doStop(Map<String, ? extends Lifecycle> lifecycleBeans, final String beanName,
      final CountDownLatch latch, final Set<String> countDownBeanNames) {
   // 從未關閉的bean List中移除
   Lifecycle bean = lifecycleBeans.remove(beanName);
   if (bean != null) {
      String[] dependentBeans = getBeanFactory().getDependentBeans(beanName);
      // 如果該bean被其他bean依賴，優(yōu)先關閉那些bean
      for (String dependentBean : dependentBeans) {
         doStop(lifecycleBeans, dependentBean, latch, countDownBeanNames);
      }
      // Lifecycel#isRunning 需要為true才會執(zhí)行stop方法
      if (bean.isRunning()) {
           if (bean instanceof SmartLifecycle) {
              // 關閉之前先記錄，如果超時沒關閉成功 用于打印日志提醒
              countDownBeanNames.add(beanName);
              ((SmartLifecycle) bean).stop(() -> {
                 // 執(zhí)行成功countDown
                 latch.countDown();
                 // 關閉成功移除
                 countDownBeanNames.remove(beanName);
              });
           }
           else {
               // 普通Lifecycle bean直接調(diào)用stop方法
               bean.stop();
           }
       }
       else if (bean instanceof SmartLifecycle) {
            // 如何SmartLifecycle不需要關閉，直接countDown
           latch.countDown();
       }
   }
}