使用beforeExecute、afterExecute和terminated扩展ThreadPoolExecutor

1、无论任务是从run中正常返回，还是抛出一个异常而返回，afterExecute都会被调用。如果任务在完成后带有一个Error，那么就不会盗用afterExecute。

2、如果beforeExecute抛出一个RuntimeException，那么任务将不被执行，afterExecute也会被调用。

3、在线程完成关闭操作时调用terminated，也就是在所有任务都已经完成并且所有工作者线程也已经关闭后。terminated可以用来释放Executor在其生命周期里分配的各种资源，此外还可以执行发送通知、记录日志或者手机finalize统计信息等操作。

4、代码示例如下：

/**
 * Copyright (C),MZJ<br>
 * <p>
 * 线程池扩展
 *
 * @author muzhongjiang 2015年3月10日
 */
@Log4j2
public class MyThreadPool extends ThreadPoolExecutor {

    private static final int DEFAULT_CORE_POOL_SIZE = 2;
    private static final int DEFAULT_MAXIMUM_POOL_SIZE = 4;
    private static final long DEFAULT_KEEP_ALIVE_TIME = 30L;//秒
    private static final TimeUnit DEFAULT_UNIT = TimeUnit.SECONDS;//秒
    private static final BlockingQueue<Runnable> DEFAULT_WORK_QUEUE = new LinkedBlockingQueue<>(1024);

    public MyThreadPool() {
        super(DEFAULT_CORE_POOL_SIZE, DEFAULT_MAXIMUM_POOL_SIZE, DEFAULT_KEEP_ALIVE_TIME, DEFAULT_UNIT, DEFAULT_WORK_QUEUE);
    }


    public MyThreadPool(int corePoolSize,
                        int maximumPoolSize,
                        long keepAliveTime,
                        TimeUnit unit,
                        BlockingQueue<Runnable> workQueue
    ) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }

    private final ThreadLocal<Long> startTime = new ThreadLocal<Long>();
    private final AtomicLong numTasks = new AtomicLong();
    private final AtomicLong totalTime = new AtomicLong();

    @Override
    protected void beforeExecute(Thread t, Runnable r) {
        super.beforeExecute(t, r);
        log.info(String.format("执行beforeExecute方法>>>  %s: start %s", t, r));
        startTime.set(System.nanoTime());
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        try {
            long endTime = System.nanoTime();
            long taskTime = endTime - startTime.get();
            numTasks.incrementAndGet();
            totalTime.addAndGet(taskTime);
            log.info(String.format("执行afterExecute方法>>>  %s: end %s, time=%dns", t, r, taskTime));
        } finally {
            super.afterExecute(r, t);
        }
    }

    @Override
    protected void terminated() {
        try {
            log.info(String.format("Terminated方法: avg time=%dns", totalTime.get() / numTasks.get()));
        } finally {
            super.terminated();
        }
    }


    public static void main(String[] args) {
        ThreadPoolExecutor threadPoolExecutor = new MyThreadPool();
//        threadPoolExecutor.submit(() -> 1 / 0);
        threadPoolExecutor.submit(() -> System.out.println("hello world"));
        threadPoolExecutor.shutdown();
    }
}