优雅关闭

1. Java中：通过Runtime.getRuntime().addShutdownHook()注册事件，当虚拟机关闭的前调用该方法的具体逻辑进行善后；
2. Spring中：执行了ApplicationContext 的close之后，只要我们Bean配置了destroy策略，那Spring在关闭之前也会先执行我们的已实现好的destroy方法；
3. 线程池中：shutdown比shutdownNow更优雅；

动态线程池优雅关闭

非Spring管理下的ThreadPoolTaskExecutor，把自己创建出来的线程池在Spring关闭的时候，进行优雅shutdown；

public class ThreadPoolExecutorShutdownDefinition implements ApplicationListener<ContextClosedEvent> {

    /**
     * 线程中的任务在接收到应用关闭信号量后最多等待多久就强制终止，其实就是给剩余任务预留的时间， 到时间后线程池必须销毁
     */
    private static final long AWAIT_TERMINATION = 20;
    /**
     * awaitTermination的单位
     */
    private static final TimeUnit TIME_UNIT = TimeUnit.SECONDS;
    
    private final List<ExecutorService> POOLS = Collections.synchronizedList(new ArrayList<>(12));

    public void registryExecutor(ExecutorService executor) {
        POOLS.add(executor);
    }

    @Override
    public void onApplicationEvent(ContextClosedEvent event) {
        if (CollectionUtils.isEmpty(POOLS)) {
            return;
        }
        for (ExecutorService pool : POOLS) {
            pool.shutdown();
            try {
                if (!pool.awaitTermination(AWAIT_TERMINATION, TIME_UNIT)) {
                    log.warn("Timed out while waiting for executor [{}] to terminate", pool);
                }
            } catch (InterruptedException ex) {
                log.warn("Timed out while waiting for executor [{}] to terminate", pool);
                Thread.currentThread().interrupt();
            }
        }
    }
}

Spring封装过的ThreadPoolTaskExecutor，默认会优雅关闭，其实现了DisposableBean接口；