众所周知 SimpleDateFormat
线程不安全,不少朋友被其坑过。
下面是 stackoverflow 的文章 why-is-javas-simpledateformat-not-thread-safe 中的栗子。
public class ExampleClass { private static final Pattern dateCreateP = Pattern.compile("Дата подачи://s*(.+)"); private static final SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss dd.MM.yyyy"); public static void main(String[] args) { ExecutorService executor = Executors.newFixedThreadPool(100); while (true) { executor.submit(new Runnable() { @Override public void run() { workConcurrently(); } }); } } public static void workConcurrently() { Matcher matcher = dateCreateP.matcher("Дата подачи: 19:30:55 03.05.2015"); Timestamp startAdvDate = null; try { if (matcher.find()) { String dateCreate = matcher.group(1); startAdvDate = new Timestamp(sdf.parse(dateCreate).getTime()); } } catch (Throwable th) { th.printStackTrace(); } System.out.print("OK "); } } 复制代码
And result :
OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK java.lang.NumberFormatException: For input string: ".201519E.2015192E2" at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043) at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.lang.Double.parseDouble(Double.java:538) at java.text.DigitList.getDouble(DigitList.java:169) at java.text.DecimalFormat.parse(DecimalFormat.java:2056) at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1869) at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514) at java.text.DateFormat.parse(DateFormat.java:364) at com.nonscalper.webscraper.processor.av.ExampleClass.workConcurrently(ExampleClass.java:37) at com.nonscalper.webscraper.processor.av.ExampleClass$1.run(ExampleClass.java:25) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) 复制代码
每次 new
(实例化) SimpleDateFormat
。
利用 ThreadLocal
确保每个线程都可以得到单独的一个 SimpleDateFormat
。
public class DateUtil { private static final ThreadLocal<SimpleDateFormat> local = ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")); public static String format(Date date) { return local.get().format(date); } public static Date parse(String dateStr) throws ParseException { return local.get().parse(dateStr); } } 复制代码
commons-lang3
中的 FastDateFormat
。 <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>${commons-lang3-version}</version> </dependency> 复制代码
性能咋样,jmh 来一把,源码见: github.com/lets-mica/m…
# JMH version: 1.21 # VM version: JDK 1.8.0_221, Java HotSpot(TM) 64-Bit Server VM, 25.221-b11 Benchmark Mode Cnt Score Error Units newSimpleDateFormat thrpt 5 114072.841 ± 989.135 ops/s threadLocal thrpt 5 348207.331 ± 46014.175 ops/s fastDateFormat thrpt 5 434391.553 ± 7799.593 ops/s 复制代码
结果: fastDateFormat
得分最高。当然你觉得这样就完了?
在 mica 1.2.1
中我们利用 Instant
来中转 Date
使用 DateTimeFormatter
格式化。
public static final DateTimeFormatter DATETIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").withZone(ZoneId.systemDefault()); public String format(Date date) { return DATETIME_FORMATTER.format(date.toInstant()); } 复制代码
注意: DateTimeFormatter
格式化 Instant
需要指定 时区
。
# JMH version: 1.21 # VM version: JDK 1.8.0_221, Java HotSpot(TM) 64-Bit Server VM, 25.221-b11 Benchmark Mode Cnt Score Error Units fastDateFormat thrpt 5 417338.980 56543.104 ops/s toInstantFormat thrpt 5 371028.709 72059.917 ops/s 复制代码
# JMH version: 1.21 # VM version: JDK 11.0.4, OpenJDK 64-Bit Server VM, 11.0.4+10-b304.69 Benchmark Mode Cnt Score Error Units fastDateFormat thrpt 5 384637.138 7402.690 ops/s toInstantFormat thrpt 5 487482.436 12490.986 ops/s 复制代码