When converting from list to map, if a certain attribute may cause key duplication and exceptions, you can set the way to deal with this duplication

from list Turn it into map When , According to a certain attribute, it may lead to key Repeated but abnormal , You can set the way to handle this repetition --java8 Of the two, choose one , There are other requirements and other ways to achieve
        
        
        
        collect(Collectors.toMap(
                    Map.Entry::getKey,  ---key 
                    Map.Entry::getValue, ---value
                    (oldVal, newVal) -> oldVal,  --- Which one to cover
                    LinkedHashMap::new --- The object assigned by the new result
            )
            
            
            
        tData = tData.entrySet().stream().sorted(new Comparator<Map.Entry<String, List<R>>>() {
                @Override
                public int compare(Map.Entry<String, List<R>> o1, Map.Entry<String, List<R>> o2) {
                    try {
                        Date d1 = DateUtil.convertStringToDate(o1.getKey(), "yyyy-MM");
                        Date d2 = DateUtil.convertStringToDate(o2.getKey(), "yyyy-MM");
                        return d1.compareTo(d2);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return 0;
                }
            }).collect(Collectors.toMap(
                    Map.Entry::getKey,
                    Map.Entry::getValue,
                    (oldVal, newVal) -> oldVal,
                    LinkedHashMap::new
            ));