SimpleDateFormat多线程问题
http://blog.csdn.net/peterwanghao/article/details/1693682
类SimpleDateFormat可以将时间格式在java.util.Date 和string之间进行相互转换。使用parse和format方法。在程序运行中却抛出java.lang.NumberFormatException异常。
java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Long.parseLong(Long.java:415)
at java.lang.Long.parseLong(Long.java:452)
at java.text.DigitList.getLong(DigitList.java:149)
at java.text.DecimalFormat.parse(DecimalFormat.java:1068)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1388)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1156)
at java.text.DateFormat.parse(DateFormat.java:333)
检查了一下输入的字串内容并没有错误。后来发现问题的根本原因是将SimpleDateFormat定义为静态属性了,多线程调用。查看了资料知道时间格式不是同步的,应当为每个线程单独创建一个实例,如果需要多线程并发地访问一个SimpleDateFormat,必须要线程同步。
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http://stackoverflow.com/questions/4021151/java-dateformat-is-not-threadsafe-what-does-this-leads-to
Here is a program in which multiple threads use a shared SimpleDateFormat
.
1 public static void main(String[] args) throws Exception { 2 3 final DateFormat format = 4 new SimpleDateFormat("yyyyMMdd"); 5 6 Callable<Date> task = new Callable<Date>(){ 7 public Date call() throws Exception { 8 return format.parse("20101022"); 9 } 10 }; 11 12 //pool with 5 threads 13 ExecutorService exec = Executors.newFixedThreadPool(5); 14 List<Future<Date>> results = 15 new ArrayList<Future<Date>>(); 16 17 //perform 10 date conversions 18 for(int i = 0 ; i < 10 ; i++){ 19 results.add(exec.submit(task)); 20 } 21 exec.shutdown(); 22 23 //look at the results 24 for(Future<Date> result : results){ 25 System.out.println(result.get()); 26 } 27 }
Run this a few times and you will see:
Exceptions:
Here are a few examples:
1 Caused by: java.lang.NumberFormatException: For input string: "" 2 at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48) 3 at java.lang.Long.parseLong(Long.java:431) 4 at java.lang.Long.parseLong(Long.java:468) 5 at java.text.DigitList.getLong(DigitList.java:177) 6 at java.text.DecimalFormat.parse(DecimalFormat.java:1298) 7 at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1589)
1 Caused by: java.lang.NumberFormatException: For input string: ".10201E.102014E4" 2 at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1224) 3 at java.lang.Double.parseDouble(Double.java:510) 4 at java.text.DigitList.getDouble(DigitList.java:151) 5 at java.text.DecimalFormat.parse(DecimalFormat.java:1303) 6 at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1589)
1 Caused by: java.lang.NumberFormatException: multiple points 2 at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1084) 3 at java.lang.Double.parseDouble(Double.java:510) 4 at java.text.DigitList.getDouble(DigitList.java:151) 5 at java.text.DecimalFormat.parse(DecimalFormat.java:1303) 6 at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1936) 7 at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1312)
Incorrect Results:
Sat Oct 22 00:00:00 BST 2011 Thu Jan 22 00:00:00 GMT 1970 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Thu Oct 22 00:00:00 GMT 1970 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010
Correct Results:
Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010 Fri Oct 22 00:00:00 BST 2010
Another approach to safely use DateFormats in a multi-threaded environment is to use a ThreadLocal
variable to hold the DateFormat
object, which means that each thread will have its own copy and doesn't need to wait for other threads to release it. This is how:
1 public class DateFormatTest { 2 3 private static final ThreadLocal<DateFormat> df 4 = new ThreadLocal<DateFormat>(){ 5 @Override 6 protected DateFormat initialValue() { 7 return new SimpleDateFormat("yyyyMMdd"); 8 } 9 }; 10 11 public Date convert(String source) 12 throws ParseException{ 13 Date d = df.get().parse(source); 14 return d; 15 } 16 }