如何转换列表<map<string, string> &gt; 列出<map<string, map<string, string> &gt;&gt; </map<string,></map<string,>

Question

Can some on tell me how to convert List<Map<String, String>> to List<Map<String, Map<String, String>>> , the key in converted map object of list is one of the value in the map of list.

in short am trying to achieve below. but I am getting null values in list.

List<Object> finalStatus = status.stream().map(map->new HashMap<>().put(map.get("testcase_mapping_run_id"), map)).collect(Collectors.toList()); ```
            
            

Answer 1

The problem is the map(map->new HashMap<>().put(map.get("testcase_mapping_run_id"), map)) . That lambda does not return the newly created map. It returns whatever put returns, which is the previous value of the key in the map . Since the map was empty, the map always returns null .

So what you want is probably

List<Map<String, Map<String, String>>> = status.stream()
    .map(map->{
        Map<String, Map<String, String>> newMap = new HashMap<>();
        newMap.put(map.get("testcase_mapping_run_id"), map);
        return newMap;
    })
    .collect(Collectors.toList());