在jdk的doc中指出SimpleDateFormat

Synchronization

public static DateFormat dataTimeFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")

考虑到该方法在工程中用的比较多，测试了几种常用方法的性能， 测试场景：单线程多次format ， 数据如下：

次数：10w

jdkSimpleDataFormat cost time: 1115ms

apacheSimpleDataFormat cost time: 275ms

threadLocalSimpleDataFormat cost time: 183ms

次数：100w

jdkSimpleDataFormat cost time: 4737ms

apacheSimpleDataFormat cost time: 1572ms

threadLocalSimpleDataFormat cost time: 853ms

次数：1000w

jdkSimpleDataFormat cost time: 35170ms

apacheSimpleDataFormat cost time: 14078ms

threadLocalSimpleDataFormat cost time: 8509ms

从数据可以看出

(1) apache common-lang提供的DateFormatUtils.format方法比JDK提供的SimpleDataFormat.format性能高出 149.82%
(2) ThreadLocal方式比 DateFormatUtils.format 方式性能高出 65.44%

结论：在使用SimpleDataFormat时，尽量使用ThreadLocal 方式。

测试代码如下，有兴趣的同学可以测下多线程情形下的性能数据。

package com.bc.perf;import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;import org.apache.commons.lang.time.DateFormatUtils;public class SimpleDataFormatPerfTest {private static final int circleNum = 10000000;private static String pattern = "yyyy-MM-dd HH:mm:ss";private Executor testExecutor = Executors.newFixedThreadPool(64);private static ThreadLocal<SimpleDateFormat> simpleDateFormatProvider = new ThreadLocal<SimpleDateFormat>() {@Overrideprotected SimpleDateFormat initialValue() {return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");}};public static void main(String[] args){SimpleDataFormatPerfTest test = new SimpleDataFormatPerfTest();SimpleDateFormat format = new SimpleDateFormat(pattern);System.out.println("jdkSimpleDataFormat date format: " + format.format(new Date()));System.out.println("apacheSimpleDataFormat date format: " + DateFormatUtils.format(new Date(), pattern));System.out.println("threadLocalSimpleDataFormat date format: " + simpleDateFormatProvider.get().format(new Date()));//1 Jdk SimpleDateFormattest.jdkSimpleDataFormatPerf();//2 Apache common-lang SimpleDateFormattest.apacheSimpleDataFormatPerf();//3 ThreadLocal SimpleDateFormattest.threadLocalSimpleDataFormatPerf();}public void jdkSimpleDataFormatPerf() {long t1 = System.currentTimeMillis();for (int i = 0; i < circleNum; i++) {SimpleDateFormat format = new SimpleDateFormat(pattern);format.format(new Date());}long t2 = System.currentTimeMillis();System.out.println("originSimpleDataFormat cost time: " + (t2 - t1));}public void apacheSimpleDataFormatPerf() {long t1 = System.currentTimeMillis();for (int i = 0; i < circleNum; i++) {DateFormatUtils.format(new Date(), pattern);}long t2 = System.currentTimeMillis();System.out.println("apacheSimpleDataFormat cost time: " + (t2 - t1));}public void threadLocalSimpleDataFormatPerf() {long t1 = System.currentTimeMillis();for (int i = 0; i < circleNum; i++) {simpleDateFormatProvider.get().format(new Date());}long t2 = System.currentTimeMillis();System.out.println("threadLocalSimpleDataFormat cost time: " + (t2 - t1));}
}