HashMap<String,String> details=new HashMap<>();
            switch(value){
                case "approved":
                    if(rs!=null) {
                        HashMap<Integer, HashMap<String, String>> detailsall = new HashMap<>();
                        int i = 1;
                        while(rs.next()) {                          
                            String NO = rs.getString("NO");
                            String CLASS = rs.getString("CLASS");
                            String CLASS_DESC = rs.getString("CLASS_DESC");

                            details.put("NO", NO);
                            details.put("CLASS", CLASS);
                            details.put("CLASS_DESC", CLASS_DESC);
                                                    
                            System.out.println(details);
                            detailsall.put(i,details);
                            System.out.println(detailsall);
                        }
                        for (Map.Entry<Integer, HashMap<String, String>> detailsallmap : detailsall.entrySet()) {
                            System.out.println(detailsallmap.getKey() + " = "+ detailsallmap.getValue());
                        }
                    }else {
                        details=null;
                    }
                    break;            
            }

Iterating over each entry of resultset and add to hashmap and that hashmap adding as nested map.
But its adding as only last entry to nested hashmap.

1. details is main hashmap where adding resultset entries

2. detailsall is nestedmap where adding details hashmap entries