java – 在测试中重现SimpleDateFormat非线程安全性

java.lang.ArrayIndexOutOfBoundsException: 514
        at sun.util.calendar.BaseCalendar.getCalendarDateFromFixedDate(BaseCalendar.java:436)
        at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2081)
        at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:1996)
        at java.util.Calendar.complete(Calendar.java:1312)
        at java.util.Calendar.get(Calendar.java:1093)
        at java.text.SimpleDateFormat.subFormat(SimpleDateFormat.java:917)
        at java.text.SimpleDateFormat.format(SimpleDateFormat.java:824)
        at java.text.SimpleDateFormat.format(SimpleDateFormat.java:796)
        at java.text.DateFormat.format(DateFormat.java:314)
        at me.myself.i.Message.toString(Message.java:203)
        at java.lang.String.valueOf(String.java:2615)
        at java.lang.StringBuilder.append(StringBuilder.java:116)

我认为这个问题可能存在于某些方面：

public class Message{
private transient DateFormat logDateFormat;
    @Override
    public String toString() {
        final StringBuilder result = new StringBuilder(getClass().getSimpleName());
        result.append("Time=").append(logDateFormat.format(new Date(getExpireTime())));     
        return result.toString();
    }
}

我认为多个线程同时调用toString(),但我在本地机器上重现这个问题：

@Before
  public void setUp() {
    message = new Message();
    pool = Executors.newFixedThreadPool(numOfThreads);
 }

  @Test
  public void multiThreadTest() {
        for (int i=0; i<numOfThreads; i++) {
            TestJob j = new TestJob(message);
            pool.submit(j);
        }
        pool.shutdown();
        while(!pool.isTerminated()){            
        }
    }

    class TestJob implements Runnable{

        private Message message;
        private int n=100;

        public TestJob(Message message) {
            this.message= message;
        }

        public void run() {
            for (int i=0; i<n; i++) {
                try{
                    System.out.println(message.toString());
                } catch(Exception e){
                    e.printStackTrace();
                }
            }
        }
    }

如何编写正确的junit测试来重现此问题？