SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner.
From the JavaDoc,
But Date formats are not synchronized. It is recommended to create
separate format instances for each thread. If multiple threads access
a format concurrently, it must be synchronized externally.
To make the SimpleDateFormat class thread-safe, look at the following approaches :
- Create a new SimpleDateFormat instance each time you need to use one. Although this is thread safe, it is the slowest possible approach.
- Use synchronization. This is a bad idea because you should never choke-point your threads on a server.
- Use a ThreadLocal. This is the fastest approach of the 3 (see http://www.javacodegeeks.com/2010/07/java-best-practices-dateformat-in.html).
