KeepAlive Class — spring-boot Architecture

Source Code

core/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java lines 1699–1739

	private static final class KeepAlive implements ApplicationListener<ApplicationContextEvent> {

		private final AtomicReference<@Nullable Thread> thread = new AtomicReference<>();

		@Override
		public void onApplicationEvent(ApplicationContextEvent event) {
			if (event instanceof ContextRefreshedEvent) {
				startKeepAliveThread();
			}
			else if (event instanceof ContextClosedEvent) {
				stopKeepAliveThread();
			}
		}

		private void startKeepAliveThread() {
			Thread thread = new Thread(() -> {
				while (true) {
					try {
						Thread.sleep(Long.MAX_VALUE);
					}
					catch (InterruptedException ex) {
						break;
					}
				}
			});
			if (this.thread.compareAndSet(null, thread)) {
				thread.setDaemon(false);
				thread.setName("keep-alive");
				thread.start();
			}
		}

		private void stopKeepAliveThread() {
			Thread thread = this.thread.getAndSet(null);
			if (thread == null) {
				return;
			}
			thread.interrupt();
		}

	}