Java应用实现优雅关闭

1.实现SignalHandler
在进程被kill时收到TERM信号，对main函数的运行不会有任何影响

public class GracefulShutdownHandler implements SignalHandler {

    public void registerSignal(String signalName) {
        Signal signal = new Signal(signalName);
        Signal.handle(signal, this);
    }
 
    @Override
    public void handle(Signal signal) {
        switch (signal.getName()) {
            case "TERM":
            	// 
                break;
            case "INT":
            	//
                break;
            default:
        }
    }
}

2.ShutdownHook
在进程被kill的时候main函数就已经结束，仅会运行shutdownHook中run()方法的代码。

Runtime.getRuntime().addShutdownHook(new Thread() {
    @Override
    public void run() {
    	//
    }
});

3.SpringBoot优雅关闭
实现TomcatConnectorCustomizer接口，用于注入tomcat的connector，tomcat通过connector接受请求

public class GracefulShutdown implements TomcatConnectorCustomizer, ApplicationListener<ContextClosedEvent> {
	private volatile Connector connector;
	private final int waitTime = 20;

    /**
     * 实现TomcatConnectorCustomizer接口，用于获取tomcat用于接收请求的connector
     */
	@Override
	public void customize(Connector connector) {
		this.connector = connector;
	}
	
    /**
     * 实现ApplicationListener<ContextClosedEvent>接口，用于监听应用的关闭事件
     */
	@Override
	public void onApplicationEvent(ContextClosedEvent event) {
		// tomcat通过connector接收请求，当服务停止时先将connector停止，不接受新的请求
		this.connector.pause();
		java.util.concurrent.Executor executor = this.connector.getProtocolHandler().getExecutor();
		if (executor instanceof ThreadPoolExecutor) {
			try {
				ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) executor;
				threadPoolExecutor.shutdown();
				if (!threadPoolExecutor.awaitTermination(waitTime, TimeUnit.SECONDS)) {
					log.warn("Tomcat thread pool did not shut down gracefully within "
							+ waitTime + " seconds. Proceeding with forceful shutdown");
				}
			} catch (InterruptedException ex) {
				Thread.currentThread().interrupt();
			}
		}
		
		// 关闭其他....
	}
}

SpringBoot 1.5.x

    /**
     * 用于注入 connector
     */
    @Bean
    public EmbeddedServletContainerCustomizer tomcatCustomizer() {
        return new EmbeddedServletContainerCustomizer() {
            @Override
            public void customize(ConfigurableEmbeddedServletContainer container) {
                if (container instanceof TomcatEmbeddedServletContainerFactory) {
                    ((TomcatEmbeddedServletContainerFactory) container).addConnectorCustomizers(gracefulShutdown());
                }
            }
        };
    }

SpringBoot 2.x.x

    /**
     * tomcat connector注入到GracefulShutdownHandler
     */
    @Bean
    public WebServerFactoryCustomizer webServerFactoryCustomizer() {
        return new WebServerFactoryCustomizer() {
            @Override
            public void customize(WebServerFactory factory) {
                if (factory instanceof TomcatServletWebServerFactory) {
                    ((TomcatServletWebServerFactory) factory).addConnectorCustomizers(gracefulShutdownHandler());
                }
            }
        };
    }