java simpledateformat not threadsafe python in ubuntue usage

SimpleDateFormat is not threadsafe, so when we use it in the a multiple threads environment, be careful.

Follow is a JAVA class to demo the error:

public class SimpleDateFormatThreadUnsafetyExample {

    private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");  ## the evil here,it is not thread safe

    public static void main(String[] args) {
        String dateStr = "2018-06-22T10:00:00";

        ExecutorService executorService = Executors.newFixedThreadPool(10);
        Runnable task = () -> parseDate(dateStr);

        for (int i = 0; i < 100; i++) {
            executorService.submit(task);
        }

        executorService.shutdown();
    }

    private static void parseDate(String dateStr) {
        try {
            Date date = simpleDateFormat.parse(dateStr);
            System.out.println("Successfully Parsed Date " + date);
        } catch (ParseException e) {
            System.out.println("ParseError " + e.getMessage());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Run it, let’s see what happeded?Following errors:

java.lang.NumberFormatException: For input string: "20182018E"
    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:2084)
    at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1869)
    at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
    at java.text.DateFormat.parse(DateFormat.java:364)
    at io.qkits.dailyissues.concurrence.SimpleDateFormatThreadUnsafetyExample.parseDate(SimpleDateFormatThreadUnsafetyExample.java:28)
    at io.qkits.dailyissues.concurrence.SimpleDateFormatThreadUnsafetyExample.lambda$main$0(SimpleDateFormatThreadUnsafetyExample.java:17)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
java.lang.NumberFormatException: multiple points
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1890)
    at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
    at java.lang.Double.parseDouble(Double.java:538)
    at java.text.DigitList.getDouble(DigitList.java:169)
    at java.text.DecimalFormat.parse(DecimalFormat.java:2089)
    at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
    at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
    at java.text.DateFormat.parse(DateFormat.java:364)
    at io.qkits.dailyissues.concurrence.SimpleDateFormatThreadUnsafetyExample.parseDate(SimpleDateFormatThreadUnsafetyExample.java:28)
    at io.qkits.dailyissues.concurrence.SimpleDateFormatThreadUnsafetyExample.lambda$main$0(SimpleDateFormatThreadUnsafetyExample.java:17)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

So move the SimpleDateFormat from static field to method level, it can solve this issue,or make the pareDate function sync.

All the SimpleDateFormat method is not not thread safe?

  private static void parseDate(String dateStr) {
        try {
            Date date = simpleDateFormat.parse(dateStr);
            System.out.println("Successfully Parsed Date " + date);
        } catch (ParseException e) {
            System.out.println("ParseError " + e.getMessage());
        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println(formatDate(new Date()));
    }

    private static String formatDate(Date date){
        return simpleDateFormat.format(date);
    }