Java SimpleDateFormat 线程不安全的具体解决方法
Java SimpleDateFormat 是线程不安全的,当在多线程环境下使用一个DateFormat的时候是有问题的,如下面的例子:
package com.heaven.threadpool;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class DateFormatThreadSafe {
public static void main(String[] args) throws Exception {
final SimpleDateFormat 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());
}
}
}
上面代码可能会引起如下问题:
问题1:
Fri Oct 22 00:00:00 CST 2010
Fri Oct 22 00:00:00 CST 2010
Fri Oct 22 00:00:00 CST 2010
Mon Nov 22 00:00:00 CST 2010
Exception in thread "main" java.util.concurrent.ExecutionException: java.lang.NumberFormatException: For input string: ""
at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
at java.util.concurrent.FutureTask.get(FutureTask.java:83)
at com.heaven.threadpool.DateFormatThreadSafe.main(DateFormatThreadSafe.java:49)
Caused by: java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Long.parseLong(Long.java:424)
at java.lang.Long.parseLong(Long.java:461)
at java.text.DigitList.getLong(DigitList.java:177)
at java.text.DecimalFormat.parse(DecimalFormat.java:1298)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1589)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1312)
at java.text.DateFormat.parse(DateFormat.java:335)
at com.heaven.threadpool.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:31)
at com.heaven.threadpool.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:1)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
问题二:
Fri Oct 22 00:00:00 CST 2010
Fri Oct 22 00:00:00 CST 2010
Fri Oct 22 00:00:00 CST 2010
Exception in thread "main" java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: -1
at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
at java.util.concurrent.FutureTask.get(FutureTask.java:83)
at com.heaven.threadpool.DateFormatThreadSafe.main(DateFormatThreadSafe.java:32)
Caused by: java.lang.ArrayIndexOutOfBoundsException: -1
at java.text.DigitList.fitsIntoLong(DigitList.java:212)
at java.text.DecimalFormat.parse(DecimalFormat.java:1296)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1589)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1312)
at java.text.DateFormat.parse(DateFormat.java:335)
at com.heaven.threadpool.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:19)
at com.heaven.threadpool.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:1)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
问题三:
Sat Oct 01 00:00:00 CST 1
Sat Oct 01 00:00:00 CST 1
Sun Oct 30 00:00:00 CST 2016
Sun Oct 30 00:00:00 CST 2016
Exception in thread "main" java.util.concurrent.ExecutionException: java.lang.NumberFormatException: For input string: "E.122E22"
at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
at java.util.concurrent.FutureTask.get(FutureTask.java:83)
at com.heaven.threadpool.DateFormatThreadSafe.main(DateFormatThreadSafe.java:32)
Caused by: java.lang.NumberFormatException: For input string: "E.122E22"
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:1936)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1312)
at java.text.DateFormat.parse(DateFormat.java:335)
at com.heaven.threadpool.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:19)
at com.heaven.threadpool.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:1)
at java.u
解决方法一:把DateFormat 放到ThreadLocal中
package com.heaven.threadpool;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DateFormatTest {
private static final ThreadLocal<DateFormat> df = new ThreadLocal<DateFormat>() {
@Override
protected DateFormat initialValue() {
return new SimpleDateFormat("yyyy-MM-dd HH");
}
};
public Date convert(String source) throws ParseException {
Date d = df.get().parse(source);
return d;
}
}
解决方法二:使用线程安全的DateFormat,在Github上已经有人写了一个线程安全的,我们可以直接拿来用,请点击下面链接查看
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