java.text.SimpleDateFormat not thread safe

Question

Synchronization

Date formats are not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concur         


        

Answer 1

Thats correct. FastDateFormat from Apache Commons Lang is a nice threadsafe alternative.

Since version 3.2 it supports also parsing, before 3.2 only formatting.

Answer 2

Yes SimpleDateFormat is not thread safe and it is also recommended when you are parsing date it should access in synchronized manner.

public Date convertStringToDate(String dateString) throws ParseException {
    Date result;
    synchronized(df) {
        result = df.parse(dateString);
    }
    return result;
}

one other way is on http://code.google.com/p/safe-simple-date-format/downloads/list

Answer 3

That's true. You can find already questions concerning this issue on StackOverflow. I use to declare it as ThreadLocal:

private static final ThreadLocal<DateFormat> THREAD_LOCAL_DATEFORMAT = new ThreadLocal<DateFormat>() {
    protected DateFormat initialValue() {
        return new SimpleDateFormat("yyyyMMdd");
    }
};

and in the code:

DateFormat df = THREAD_LOCAL_DATEFORMAT.get();