The data can be stored as follows.

1. there will be a root HashMap which has NAME as key and another
HashMap as value..
2. the second HashMap will have role as key and an array list as
value..
3. the ArrayList will have list of all the resources for that user for
that particular role.

so.. the root HashMap will look like

HashMap { [NAME1, HashMap { [ROLE1, ArrayList {RES11, RES12,...} ],
                                           [ROLE2, ArrayList {RES21,
RES22,...} ],.....} ],  [NAME2, HashMap { [ROLE1, ArrayList {RES11,
RES12,...} ], [ROLE2, ArrayList {RES21, RES22, ...
                         } ], .... }

eg:

    SAM:ADMIN:LAP
    SAM:ADMIN:PEN
    SAM:USER:PC
    MIKE:USER:PC

then the storage will be like

HashMap { [SAM, HashMap { [ADMIN, ArrayList {LAP, PEN}],  [USER,
ArrayList {PC}] } ], [MIKE, HashMap { [USER, ArrayList {PC} ] } ] }

the following is a simple function which does the above logic..

public void store(Map userMap, String user, String role, String
resource) {
   Map roleMap = (Map)userMap.get(user);
   if(roleMap == null) {
       roleMap = new HashMap();
       userMap.put(user, roleMap);
   }

   List resList = (List) roleMap.get(role);
   if (resList == null) {
       resList = new ArrayList();
       roleMap.put(role, resList);
   }

   if(!resList.contains(resource)){
       resList.add(resource);
   }
}

using this you can access all the data very easily.. i guess the memory
utilization better since there is no unnecessary or duplicate data
stored. (dont know the exact memory utilization)