前言
在高并发场景下System.currentTimeMillis()并发问题严重，甚至比创建一个普通对象要耗时的多；在系统中有时候不可避免要打印一些时间戳，但怎么做才更好呢。
代码实现
代码语言：javascript复制iimport java.util.concurrent.Executors;import java.util.concurrent.ScheduledExecutorService;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicLong; /** * 高并发场景下System.currentTimeMillis()的性能问题的优化 * 时间戳打印建议使用 */public class SystemClock { private static final String THREAD_NAME = "system.clock"; private static final SystemClock MILLIS_CLOCK = new SystemClock(1); private final long precision; private final AtomicLong now; private SystemClock(long precision) { this.precision = precision; now = new AtomicLong(System.currentTimeMillis()); scheduleClockUpdating(); } public static SystemClock millisClock() { return MILLIS_CLOCK; } private void scheduleClockUpdating() { ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor(runnable -> { Thread thread = new Thread(runnable, THREAD_NAME); thread.setDaemon(true); return thread; }); scheduler.scheduleAtFixedRate(() -> now.set(System.currentTimeMillis()), precision, precision, TimeUnit.MILLISECONDS); } public long now() { return now.get(); }}调用示例 Long start = SystemClock.millisClock().now()
测试对比
代码语言：javascript复制public static void main(String[] args) { int times=Integer.MAX_VALUE; long start = System.currentTimeMillis(); for (long i = 0; i < times; i ) { SystemClock.millisClock().now(); } long end = System.currentTimeMillis(); System.out.println("SystemClock Time:" (end - start) "毫秒"); long start2 = System.currentTimeMillis(); for (long i = 0; i < times; i ) { System.currentTimeMillis(); } long end2 = System.currentTimeMillis(); System.out.println("SystemCurrentTimeMillis Time:" (end2 - start2) "毫秒"); }输出结果是: SystemClock Time:2741毫秒 SystemCurrentTimeMillis Time:14072毫秒 五倍的效率
细节决定成败，敬畏每一行代码，代码优化永无止境！
转载于:https://www.cnblogs.com/mengq0815/p/10596067.html
