统一时间工具类

系统高并发直接调用System.currentTimeMillis()存在性能问题，因此统一个后台线程维护当前时间缓存。

import org.jetbrains.annotations.NotNull;
import java.sql.Timestamp;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
/**
 * <p> 获取当前时间时钟时钟工具类 解决直接获取时间的性能问题 </p>
 *
 * @author mori
 * @since 2020/12/30 11:53
 */
public final class SystemClock {
    private final long period;
    private final AtomicLong now;
    private SystemClock(long period) {
        this.period = period;
        this.now = new AtomicLong(System.currentTimeMillis());
        this.scheduleClockUpdating();
    }
    private static SystemClock instance() {
        return InstanceHolder.INSTANCE;
    }
    public static long now() {
        return instance().currentTimeMillis();
    }
    public static String nowDate() {
        return (new Timestamp(instance().currentTimeMillis())).toString();
    }
    /**
     * 现在当地的日期时间
     *
     * @return {@link LocalDateTime}
     */
    public static LocalDateTime nowLocalDateTime() {
        Instant instant = Instant.ofEpochMilli(instance().currentTimeMillis());
        ZoneId zone = ZoneId.systemDefault();
        return LocalDateTime.ofInstant(instant, zone);
    }
    private void scheduleClockUpdating() {
        new ScheduledThreadPoolExecutor(1, new UpdateThreadDaemonFactory()
        ).scheduleAtFixedRate(() -> {
            now.set(System.currentTimeMillis());
        }, this.period, this.period, TimeUnit.MILLISECONDS);
    }
    private long currentTimeMillis() {
        return this.now.get();
    }
    public static class UpdateThreadDaemonFactory implements ThreadFactory {
        private static int threadInitNumber = 0;
        private static synchronized int nextThreadNum() {
            return threadInitNumber++;
        }
        @Override
        public Thread newThread(@NotNull Runnable r) {
            Thread thread = new Thread(r, "Thread-System-Lock-" + nextThreadNum());
            thread.setDaemon(true);
            return thread;
        }
    }
    private static class InstanceHolder {
        private static final SystemClock INSTANCE = new SystemClock(1L);
        private InstanceHolder() {
        }
    }
}