如何从LinkedHashMap中删除空值 <String,Object> 嵌套对象具有空值

Question

My JSON Doc is structured like this and being saved in MongoDB with null values.

{
"userId": "123456",
"session": "string",
"timestamp": 0,
"product": "tracker",
"version": "13",
"flight": "A",
"activity": "search",
"action": "opportunity",
"dataDictionary": {
    "datadictionary": {
        "query": "roofing",
        "docid": 12,
        "rank": 1,
        "search": {
            "id": null
        }
    },
    "id": 40
}

I have also tried to put @JsonInclude(JsonInclude.Include.NON_NULL)

My Hash map is declared like

Map<String, Object >dataDict = new LinkedHashMap<>();
dataDict.values().removeIf(Objects::isNull);

As far as I can tell this should be removing all null values regardless of level/layer in the Map.

JSON is stored like this

{

"userId": "123456",
"session": "string",
"timestamp": 0,
"product": "tracker",
"version": "13",
"flight": "A",
"activity": "search",
"action": "opportunity",
"dataDictionary": {
    "datadictionary": {
        "query": "roofing",
        "docid": 12,
        "rank": 1,
        "search": {
            "id": null,
            "name":"test"
        }
    },
    "id": 40
}

Should be stored like this

{
"userId": "123456",
"session": "string",
"timestamp": 0,
"product": "tracker",
"version": "13",
"flight": "A",
"activity": "search",
"action": "opportunity",
"dataDictionary": {
    "datadictionary": {
        "query": "roofing",
        "docid": 12,
        "rank": 1,
        "search": {
            "name":"test"
        }
    },
    "id": 40
}

Answer 1

The problem is that you are removing null values from the top level Map.

This map contains internally values that are other maps. You don't remove null values from thos maps.

Try to use a recursive function to remove all null elements from inner maps.

The json:

{
   "topField": null,
   "innerMap": {
      "innerField": null
   }

}

is equivalent to the following maps in java

Map map = new LinkedHashMap();
map.put("topField", null);
Map innerMap = new LinkedHashMap();
innerMap.put("innerField", null);
map.put("innerMap", innerMap);

If you apply the code to remove null values to map:

map.values().removeIf(Objects::isNull);

results in a map that is equivalent to the following manually built map:

Map map = new LinkedHashMap();
// map.put("topField", null);
Map innerMap = new LinkedHashMap();
innerMap.put("innerField", null);
map.put("innerMap", innerMap);

because it removes null values from the map, not from innerMap.

You can remove all null elements at any level as follow:

public void removeNull(Map map) {
   map.values().removeIf(Objects::isNull);
   for (Object value: map.values()) {
       if (value instanceof Map) {
         // Apply a recursion on inner maps
         removeNull((Map) value);
       }
   }
} 

And you can remove all null items as follow:

Map map = ...
removeNull(map); 

Answer 2

As mentioned by others, you would need to do it in a recursive manner. For example, if you have function like removeNulls :

private boolean removeNulls(final Object o) {
    if (Objects.isNull(o)) {
        return true;
    } else if (o instanceof Map) {
        ((Map) o).values().removeIf(MyClass::removeNulls);
    }
    return false;
}

Then, you could do it like:

dataDict.values().removeIf(MyClass::removeNulls);

This is just to serve as an example.