Java SimpleDateFormat线程不安全问题

public class DateTest {
    //工具类中的日期组件
    private static final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");


    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10, 100, 1, TimeUnit.MINUTES, new LinkedBlockingQueue<>(10));
        for (int i = 0; i < 100; i++) {
            threadPoolExecutor.execute(() -> {
                String dateString = sdf.format(new Date());
                try {
                    Date parseDate = sdf.parse(dateString);
                    String dateString2 = sdf.format(parseDate);
                    System.out.println(dateString.equals(dateString2));
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
        }
    }
}

public class DateTest {
    //工具类中的日期组件
//    private static final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    private static final FastDateFormat sdf = FastDateFormat.getInstance("yyyy-MM-dd HH:mm:ss");

    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10, 100, 1, TimeUnit.MINUTES, new LinkedBlockingQueue<>(10));
        for (int i = 0; i < 100; i++) {
            threadPoolExecutor.execute(() -> {
                String dateString = sdf.format(new Date());
                try {
                    Date parseDate = sdf.parse(dateString);
                    String dateString2 = sdf.format(parseDate);
                    System.out.println(dateString.equals(dateString2));
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
        }
        threadPoolExecutor.shutdown();
    }
}

public static void main(String[] args) throws Exception {
    ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10, 100, 1, TimeUnit.MINUTES, new LinkedBlockingQueue<>(10));
    for (int i = 0; i < 100; i++) {
        threadPoolExecutor.execute(() -> {
            try {
                String dateString = sdf.format(LocalDateTime.now());
                TemporalAccessor temporalAccessor = sdf.parse(dateString);
                String dateString2 = sdf.format(temporalAccessor);
                System.out.println(dateString.equals(dateString2));
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
    }
    threadPoolExecutor.shutdown();
}