It is possible, provided you use Tomcat version 7 or later.
With this version was added a landingPage
attribute to the FormAuthenticator
which should do what you want from the description :
Controls the behavior of the FORM authentication process if the process is misused, for >example by directly requesting the login page or delaying logging in for so long that the >session expires. If this attribute is set, rather than returning an error response code, >Tomcat will redirect the user to the specified landing page if the login form is >submitted with valid credentials.
To add that attribute, you will have to modify your <Context>
to add, for example:
<Valve className="org.apache.catalina.authenticator.FormAuthenticator" landingPage="exemple.jsp" />
with exemple.jsp
under a security-constraint.