线程池单例模式实现的两种方式

1. 使用enum枚举数据类型实现单例模式

public enum GroovyTimer {
    INSTANCE;

    private final AtomicInteger cacheTaskNumber = new AtomicInteger(1);
    private ScheduledExecutorService pruneTimer;

    GroovyTimer() {
        this.create();
    }

    public ScheduledFuture<?> schedule(Runnable task, long delay) {
        return this.pruneTimer.scheduleAtFixedRate(task, delay, delay, TimeUnit.MILLISECONDS);
    }

    public void create() {
        if (null != this.pruneTimer) {
            this.shutdownNow();
        }

        this.pruneTimer = new ScheduledThreadPoolExecutor(1,
                (r) -> newGroovyThread(r, String.format("Groovy-Timer-%s", this.cacheTaskNumber.getAndIncrement())));
    }
    //
    public Thread newGroovyThread(Runnable runnable, String name) {
        Thread t = newThread(runnable, name, false);
        if (t.getPriority() != 5) {
            t.setPriority(5);
        }

        return t;
    }

    public static Thread newThread(Runnable runnable, String name, boolean isDaemon) {
        Thread t = new Thread(null, runnable, name);
        t.setDaemon(isDaemon);
        return t;
    }


    public void shutdown() {
        if (null != this.pruneTimer) {
            this.pruneTimer.shutdown();
        }

    }

    public List<Runnable> shutdownNow() {
        return null != this.pruneTimer ? this.pruneTimer.shutdownNow() : null;
    }
}

2. 使用静态内置类实现单例模式

public class DukeFileCleanThreadPool {
    private final ScheduledThreadPoolExecutor executorService;

    private DukeFileCleanThreadPool() {
        executorService = new ScheduledThreadPoolExecutor(2,
                new BasicThreadFactory.Builder().namingPattern("Guard-file-clean-pool-%d").build());
    }

    private static class SingletonHolder {
        private static final GuardFileCleanThreadPool INSTANCE = new GuardFileCleanThreadPool();
    }

    public static DukeFileCleanThreadPool getInstance() {return SingletonHolder.INSTANCE;}

    public void executeTask(Runnable command, long initialDelay, long period) {
        executorService.scheduleAtFixedRate(command, initialDelay, period, TimeUnit.MILLISECONDS);
        log.info("initiate file clean timer");
    }
}