I am not an LDAP expert. However the dependency on LDAP can be removed. It is possible in your application, the LDAP is the only solution for the authentication and authroization. If you can use isUserInRole , it means you are using Container managed authroization and authentication. Based on that assumption, the servlet should not get to know where is the LDAP server.
To show which page for which role is a business pure issue. It is predetermined in the design.
If I had this issue, it is possible I would design a role -> display page mapping config file. Or to see if there is anything available in the current framework for it. Based on that , the servlet just read the config information from a java
bean and test
if the user is in the role and what should be the next page.
If one day the Realm was changed to Database realm , the code would not have to be changed.
Just my 2 cents