No. The declaration of variables in JSP is not thread-safe, because the
declared variables end up in the generated Servlet as an instance variable, not
within the body of the _jspservice() method.
The following declaration is not thread safe: because these are declarations, and will only be evaluated once when the page is loaded
<%! int a = 6 %>
The following declaration is thread safe: because the variables declared inside the scriplets have the local scope and not shared.
<% int a = 6 %>;