The isThreadSafe directive is no longer recommended

In Jakarta Server Pages 3.1, the isThreadSafe page directive is no longer recommended. isThreadSafe is implemented differently in JSP 3.1, and it can result in severe performance issues.

For more information about isThreadSafe, see the Jakarta Server Pages 3.1 Specification

For more Jakarta 10 migration information, see Differences between Jakarta Server Pages and 3.1 and 3.0.