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我的应用程序并行处理一堆文件，并且由于每个文件都有文件作为其名称的一部分被删除的日期，因此我使用以下方法来提取删除日期：Java - 静态方法的线程安全
public static Optional<Date> getFileDropDate(String filename) {
/* Example: my_file-1_20171002.xml */
if (StringUtils.isEmpty(filename) || !filename.matches(Constants.FILE_DATE_PATTERN)) {
return Optional.empty();
}
String[] segments = filename.split(UNDERSCORE);
try {
// Filename definitely ends with _yyyyMMdd.xml as it matches the pattern. Split by underscore, get the last segment and take out the .xml
return Optional.of(yyyymmdd.parse(segments[segments.length - 1].replace(Constants.XML_EXTENSION, "")));
} catch (ParseException e) {
logger.error("Unable to parse filename to find load date");
return Optional.empty();
}
}
虽然功能是非常稳固和我的测试都是成功的，当我在多线程设置运行它，它失败了日期解析例外，并且该方法试图解析字符串是完全不可思议。
例如：
java.lang.NumberFormatException: For input string: "E.21616"
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:2162)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at mycompany.importer.parser.ParserUtil.getFileDropDate(ParserUtil.java:308)
at mycompany.dataprocessors.FileProcessor.lambda$importData$2(FileProcessor.java:181)
at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:291)
at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
2017-10-21 22:11:48.550 [ForkJoinPool.commonPool-worker-2] ERROR a.c.t.m.m.a.m.i.d.FileProcessor - Error in parsing files and building datamap. Feed file is: /files/my_file_1-db_20171016.xml
java.lang.NumberFormatException: For input string: "E.21616E2"
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:2162)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at mycompany.importer.parser.ParserUtil.getFileDropDate(ParserUtil.java:308)
at mycompany.dataprocessors.FileProcessor.lambda$importData$2(FileProcessor.java:181)
at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:291)
at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
2017-10-21 22:11:48.550 [ForkJoinPool.commonPool-worker-3] ERROR a.c.t.m.m.a.m.i.d.FileProcessor - Error in parsing files and building datamap. Feed file is: /files/my_file_2-db_20171020.xml
java.lang.NumberFormatException: For input string: "20172017E4"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Long.parseLong(Long.java:589)
at java.lang.Long.parseLong(Long.java:631)
at java.text.DigitList.getLong(DigitList.java:195)
at java.text.DecimalFormat.parse(DecimalFormat.java:2051)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1867)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at mycompany.importer.parser.ParserUtil.getFileDropDate(ParserUtil.java:308)
at mycompany.dataprocessors.FileProcessor.lambda$importData$2(FileProcessor.java:181)
at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:291)
at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
制作方法进行同步解决了这个问题，但考虑到这种方法不使用或修改任何实例变量（如果这不是明显在常量全部的变量是公共static final），每个线程在技术上都有自己的局部变量栈，为什么这个方法不是线程安全的？
'yyyymmdd'有可能是'static'对象吗？这就是原因，这个类不是为多线程而设计的，* *有*实例值。我的€0.02：*避免静态*。 –