com.dahuatech.hutool.core.date.SystemClock Maven / Gradle / Ivy
package com.dahuatech.hutool.core.date;
import java.sql.Timestamp;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
/**
* 系统时钟
* 高并发场景下System.currentTimeMillis()的性能问题的优化
* System.currentTimeMillis()的调用比new一个普通对象要耗时的多（具体耗时高出多少我还没测试过，有人说是100倍左右）
* System.currentTimeMillis()之所以慢是因为去跟系统打了一次交道 后台定时更新时钟，JVM退出时，线程自动回收
*
* see： http://git.oschina.net/yu120/sequence
*
* @author lry,looly
*/
public class SystemClock {
/** 时钟更新间隔，单位毫秒 */
private final long period;
/** 现在时刻的毫秒数 */
private volatile long now;
/**
* 构造
*
* @param period 时钟更新间隔，单位毫秒
*/
private SystemClock(long period) {
this.period = period;
this.now = System.currentTimeMillis();
scheduleClockUpdating();
}
/**
* 单例实例
*
* @return 单例实例
*/
private static SystemClock instance() {
return InstanceHolder.INSTANCE;
}
/** @return 当前时间 */
public static long now() {
return instance().currentTimeMillis();
}
// ------------------------------------------------------------------------ static
/** @return 当前时间字符串表现形式 */
public static String nowDate() {
return new Timestamp(instance().currentTimeMillis()).toString();
}
/** 开启计时器线程 */
private void scheduleClockUpdating() {
ScheduledExecutorService scheduler =
Executors.newSingleThreadScheduledExecutor(
new ThreadFactory() {
@Override
public Thread newThread(Runnable runnable) {
Thread thread = new Thread(runnable, "System Clock");
thread.setDaemon(true);
return thread;
}
});
scheduler.scheduleAtFixedRate(
new Runnable() {
@Override
public void run() {
now = System.currentTimeMillis();
}
},
period,
period,
TimeUnit.MILLISECONDS);
}
/** @return 当前时间毫秒数 */
private long currentTimeMillis() {
return now;
}
/**
* 单例
*
* @author Looly
*/
private static class InstanceHolder {
public static final SystemClock INSTANCE = new SystemClock(1);
}
}