背景

服務(wù)能被優(yōu)雅停機(jī)辙喂，指的是：在接收到停機(jī)指令后摹菠，服務(wù)程序應(yīng)該能拒絕新的請(qǐng)求, 但應(yīng)該繼續(xù)完成已經(jīng)接收請(qǐng)求囊扳。

解決方案

Graceful Shutdown Spring Boot Applications 這篇文章提供了一個(gè)經(jīng)典的實(shí)現(xiàn)優(yōu)雅停機(jī)的實(shí)現(xiàn)尿贫。

import org.apache.catalina.connector.Connector;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.web.embedded.tomcat.TomcatConnectorCustomizer;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextClosedEvent;
import java.util.concurrent.Executor;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class GracefulShutdown implements TomcatConnectorCustomizer, ApplicationListener<ContextClosedEvent> {
    private static final Logger log = LoggerFactory.getLogger(GracefulShutdown.class);
    private volatile Connector connector;
    @Override
    public void customize(Connector connector) {
        this.connector = connector;
    }
    @Override
    public void onApplicationEvent(ContextClosedEvent event) {
        this.connector.pause();
        Executor executor = this.connector.getProtocolHandler().getExecutor();
        if (executor instanceof ThreadPoolExecutor) {
            try {
                ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) executor;
                threadPoolExecutor.shutdown();
                if (!threadPoolExecutor.awaitTermination(30, TimeUnit.SECONDS)) {
                    log.warn("Tomcat thread pool did not shut down gracefully within "
                            + "30 seconds. Proceeding with forceful shutdown");
                }
            } catch (InterruptedException ex) {
                Thread.currentThread().interrupt();
            }
        }
    }
}

以上代碼實(shí)現(xiàn)了兩個(gè)功能：

1. 實(shí)現(xiàn)TomcatConnectorCustomizer往毡，作用是獲取tomcat的connector个少，方便后續(xù)對(duì)tomcat的連接做操作洪乍。
2. 實(shí)現(xiàn)ApplicationListener，監(jiān)聽ApplicationContext發(fā)布的事件夜焦，該例中監(jiān)聽的是ContextClosedEvent事件壳澳，監(jiān)聽到此類事件后把tomcat中connector的線程池shutdown并等待30s，如果所有線程都結(jié)束則正常退出茫经，否則發(fā)出報(bào)警巷波。這里也體現(xiàn)了設(shè)計(jì)模式中的觀察者模式，實(shí)現(xiàn)交互對(duì)象之間的松耦合卸伞。

設(shè)計(jì)好listener之后還需要將該listener注冊(cè)到ApplicationContext中，方便其接受ApplicationContext發(fā)布的事件荤傲。同時(shí)還需將該listener注冊(cè)到tomcat中垮耳，方便獲取該Spring應(yīng)用集成的tomcat的connector终佛。注冊(cè)的代碼如下：

@Bean
public GracefulShutdown gracefulShutdown() {
    return new GracefulShutdown();
}
@Bean
public ConfigurableServletWebServerFactory webServerFactory(final GracefulShutdown gracefulShutdown) {
    TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
    factory.addConnectorCustomizers(gracefulShutdown);
    return factory;
}