public class MyCache {
        static ConcurrentHashMap<String, NavigableMap <Long, String>> map1= new ConcurrentHashMap<String, NavigableMap <Long, String>> ();
        static HashMap <String, NavigableMap <Long, String>> map2= new ConcurrentHashMap<String, NavigableMap <Long, String>> ();
        static ConcurrentHashMap<String, NavigableMap <Long, String>> map3= new ConcurrentHashMap<String, NavigableMap <Long, String>> ();
        static ConcurrentHashMap<String, NavigableMap <Long, String>> map4= new ConcurrentHashMap<String, NavigableMap <Long, String>> ();
        static ConcurrentHashMap<String, NavigableMap <Long, String>> map5= new ConcurrentHashMap<String, NavigableMap <Long, String>> ();
        static ConcurrentHashMap<String, NavigableMap <Long, String>> map6= new ConcurrentHashMap<String, NavigableMap <Long, String>> ();
        static ConcurrentHashMap<String, NavigableMap <Long, String>> map7= new ConcurrentHashMap<String, NavigableMap <Long, String>> ();

        public static void main(String[] args) throws Exception {
    new Server(); //new server thread accessing caches
    for (int i =0 ; i< users.length; i++) //cache data for each username
         new Caching();
    }
}

MyCache.map1.put(username, new ConcurrentSkipListMap <Long, String> (map1Temp));

//...
    switch (type) {
            case "type1":
                list = new ArrayList<String>(MyCache.map1.get(username).subMap(start, end).values());
                break;

            case "type2":
                list = new ArrayList<String>(MyCache.map2.get(username).subMap(start, end).values());
                break;
    // ...
            case "type7":
                list = new ArrayList<String>(MyCache.map7.get(username).subMap(start, end).values());
                break;
//and send the array as text over HTTP