技术细节之SimpleDateFormat线程安全问题

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.

http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6231579

Sun refused to accept this issue as a BUG, so we have to handle the thread-safe by ourselves.

REF：http://jroller.com/page/dschneller?entry=calendar_dateformat_and_multi_threading

java.util.Calendar也存在这个问题，更差的是，其Javadoc中一字也未提到。

搜索代码中static Calender和static SimpleDateFormat吧，隐患啊，而且一般测试测不出来的。