Migrating from Tomcat 7.0.x

Migrating from Tomcat 7.0.x is described at  https://tomcat.apache.org/migration-8.html.

RequestScope

As documented at https://tomcat.apache.org/migration-8.html:

JavaServer Pages 2.3

Unified Expression Language 3.0 added support for referencing static fields and methods. Supporting this feature in JSPs required changing the javax.servlet.jsp.el.ScopedAttributeELResolver implementation so that it also checked identifiers to see if they were names of imported classes or fields. In some circumstances, this change triggers significant slow down. This affects identifiers that may refer to a page, request, session or application scoped variable or may be undefined. When undefined, it takes significantly longer to resolve the identifier since it is now also checked to see if it is an imported class or field. To avoid this slow down, code such as:

${undefined}

should be replaced with:

${requestScope.undefined}

or similar, using the appropriate scope for where the variable is defined.