This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
In a JSP, the natural way to format a date is to use JSTL's <fmt:formatDate> element. There's also a <fmt:parseDate> element to parse a string into a date. Both of them support anything that the SimpleDateFormat object supports.
It looks to me like you would need both of those elements; <fmt:parseDate> to parse your string into a date based on one pattern, then <fmt:formatDate> to format it for output using a different pattern.