SpringBoot 从2.3.0.RELEASE 开始支持 web 服务器的优雅停机
看看官方文档是怎么介绍这一新特性的
“ Graceful shutdown is supported with all four embedded web servers (Jetty, Reactor Netty, Tomcat, and Undertow) and with both reactive and Servlet-based web applications. It occurs as part of closing the application context and is performed in the earliest phase of stopping SmartLifecycle beans. This stop processing uses a timeout which provides a grace period during which existing requests will be allowed to complete but no new requests will be permitted. The exact way in which new requests are not permitted varies depending on the web server that is being used. Jetty, Reactor Netty, and Tomcat will stop accepting requests at the network layer. Undertow will accept requests but respond immediately with a service unavailable (503) response."
四种内嵌 web 服务器(Jetty、Reactor Netty、Tomcat 和 Undertow)以及 reactive 和基于 servlet 的 web 应用程序都支持优雅停机，它作为关闭应用程序上下文的一部分发生，并且是SmartLifecyclebean里最早进行关闭的。此停止处理会有个超时机制，该超时提供了一个宽限期，在此期间允许完成现有请求，但不允许新请求。具体实现取决于所使用的web服务器。Jetty、Reactor Netty 和 Tomcat 将停止接受网络层的请求。Undertow 将接受请求，但立即响应服务不可用(503）。
server:
# 设置关闭方式为优雅关闭
shutdown: graceful
spring:
lifecycle:
# 优雅关闭超时时间, 默认30s
timeout-per-shutdown-phase: 30s
在 Java 程序中可以通过添加钩子，在程序退出时会执行钩子方法，从而实现关闭资源、平滑退出等功能。
public static void main(String[] args) {
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
@Override
public void run() {
System.out.println("执行 ShutdownHook ...");
}
}));
}
覆盖以下场景:
DestroyJavaVM方法调用说明: kill -9 会直接杀死进程不会触发 shutdownhook 方法执行，shutdownhook 回调方法会启动新线程，注册多个钩子会并发执行。