How can I implement a thread-safe JSP page?

You can make your JSPs thread-safe by having them implement the SingleThreadModel interface.
This is done by adding the directive
<%@ page isThreadSafe="false" %>
within your JSP page.

With this, instead of a single instance of the servlet generated for your JSP page loaded in memory, you will have N instances of the servlet loaded and initialized, with the service method of each instance effectively synchronized. You can typically control the number of instances (N) that are instantiated for all servlets implementingSingleThreadModel through the admin screen for your JSP engine.