SimpleDateFormat非线程安全 博客分类: Java FastDateFormatDateFormatUtilsSimpleDateFormatDate日期
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2024-03-16 16:18:10
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问题的引出,这是一个多线程访问SimpleDateFormat的测试类
public class DateUtilTest { public static class TestSimpleDateFormatThreadSafe extends Thread { @Override public void run() { while ( true ) { try { this.join(2000); } catch ( InterruptedException e1 ) { e1.printStackTrace(); } try { System.out.println(this.getName() + ":" + DateUtil.parse("2013-05-24 06:02:20")); } catch ( ParseException e ) { e.printStackTrace(); } } } } public static void main( String[] args ) { for ( int i = 0 ; i < 10 ; i++ ) { new TestSimpleDateFormatThreadSafe().start(); } } }
运行时会出现如下Exception
java.lang.NumberFormatException: For input string: "" java.lang.NumberFormatException: multiple points
原因是DateFormate类中有个Calendar变量是全局,这个变量在子类SimpleDateFormat类在两个方法中被调用
private StringBuffer format(Date date, StringBuffer toAppendTo,FieldDelegate delegate) private void subFormat(int patternCharIndex, int count,FieldDelegate delegate, StringBuffer buffer,boolean useDateFormatSymbols)
这时多线程访问就是非线程安全的
public abstract class DateFormat extends Format { protected Calendar calendar; }
解决办法:
方法一:每次创建都new一个新的
public class DateUtil { public static String formatDate(Date date)throws ParseException{ SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); return sdf.format(date); } public static Date parse(String strDate) throws ParseException{ SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); return sdf.parse(strDate); } }
方法二:使用同步
public class DateSyncUtil { private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static String formatDate(Date date)throws ParseException{ synchronized(sdf){ return sdf.format(date); } } public static Date parse(String strDate) throws ParseException{ synchronized(sdf){ return sdf.parse(strDate); } } }
方法三:使用ThreadLocal
public class ConcurrentDateUtil { private static ThreadLocal<DateFormat> threadLocal = new ThreadLocal<DateFormat>() { @Override protected DateFormat initialValue() { return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); } }; public static Date parse( String dateStr ) throws ParseException { return threadLocal.get().parse(dateStr); } public static String format( Date date ) { return threadLocal.get().format(date); } }
另一中ThreadLocal方法
public class ThreadLocalDateUtil { private static final String date_format = "yyyy-MM-dd HH:mm:ss"; private static ThreadLocal<DateFormat> threadLocal = new ThreadLocal<DateFormat>(); public static DateFormat getDateFormat() { DateFormat df = threadLocal.get(); if(df==null){ df = new SimpleDateFormat(date_format); threadLocal.set(df); } return df; } public static String formatDate(Date date) throws ParseException { return getDateFormat().format(date); } public static Date parse(String strDate) throws ParseException { return getDateFormat().parse(strDate); } }
commons-lang.jar中提供了FastDateFormt,是一个thread-safe,性能上也能还是可以的
FastDateFormat fdf = FastDateFormat.getInstance("yyyy-MM-dd", TimeZone.getDefault(), Locale.getDefault()); DateFormatUtils.ISO_DATE_FORMAT.format(new Date())
DateFormatUtils是一个FastDateFormat工具类,提供了一些format常量
ISO_DATE_FORMAT yyyy-MM-dd"2004-01-02" ISO_DATE_TIME_ZONE_FORMAT yyyy-MM-ddZZ"2004-01-02-07:00" ISO_DATETIME_FORMAT yyyy-MM-dd'T'HH:mm:ss"2004-01-02T23:22:12" ISO_DATETIME_TIME_ZONE_FORMAT yyyy-MM-dd'T'HH:mm:ssZZ"2004-01-02T21:13:45-07:00" ISO_TIME_FORMAT 'T'HH:mm:ss"T04:23:22" ISO_TIME_NO_T_FORMAT HH:mm:ss"05:12:34" ISO_TIME_NO_T_TIME_ZONE_FORMAT HH:mm:ssZZ"12:32:22-07:00" ISO_TIME_TIME_ZONE_FORMAT 'T'HH:mm:ssZZ"T18:23:22-07:00" SMTP_DATETIME_FORMAT EEE, dd MMM yyyy HH:mm:ss Z"Wed, 01 Feb 2004 20:03:01 CST"