更新时间:2022-05-26 09:18:57
我们来试试看.
这是一个多线程使用共享SimpleDateFormat
的程序.
Here is a program in which multiple threads use a shared SimpleDateFormat
.
计划:
public static void main(String[] args) throws Exception {
final DateFormat format = new SimpleDateFormat("yyyyMMdd");
Callable<Date> task = new Callable<Date>(){
public Date call() throws Exception {
return format.parse("20101022");
}
};
//pool with 5 threads
ExecutorService exec = Executors.newFixedThreadPool(5);
List<Future<Date>> results = new ArrayList<Future<Date>>();
//perform 10 date conversions
for(int i = 0 ; i < 10 ; i++){
results.add(exec.submit(task));
}
exec.shutdown();
//look at the results
for(Future<Date> result : results){
System.out.println(result.get());
}
}
运行几次,你会看到:
例外:
这里有几个例子:
1.
Caused by: java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Long.parseLong(Long.java:431)
at java.lang.Long.parseLong(Long.java:468)
at java.text.DigitList.getLong(DigitList.java:177)
at java.text.DecimalFormat.parse(DecimalFormat.java:1298)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1589)
2.
Caused by: java.lang.NumberFormatException: For input string: ".10201E.102014E4"
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1224)
at java.lang.Double.parseDouble(Double.java:510)
at java.text.DigitList.getDouble(DigitList.java:151)
at java.text.DecimalFormat.parse(DecimalFormat.java:1303)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1589)
3.
Caused by: java.lang.NumberFormatException: multiple points
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1084)
at java.lang.Double.parseDouble(Double.java:510)
at java.text.DigitList.getDouble(DigitList.java:151)
at java.text.DecimalFormat.parse(DecimalFormat.java:1303)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1936)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1312)
不正确的结果:
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
正确的结果:
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
在多线程环境中安全使用 DateFormats 的另一种方法是使用 ThreadLocal
变量来保存 DateFormat
对象,这意味着每个线程都有自己的复制,不需要等待其他线程释放它.方法如下:
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:
public class DateFormatTest {
private static final ThreadLocal<DateFormat> df = new ThreadLocal<DateFormat>(){
@Override
protected DateFormat initialValue() {
return new SimpleDateFormat("yyyyMMdd");
}
};
public Date convert(String source) throws ParseException{
Date d = df.get().parse(source);
return d;
}
}
这是一篇很好的帖子,其中包含更多详细信息.
Here is a good post with more details.