Java 8 Copy Map with Filter of Another Map - java-8

Question

I am trying to filter an original map by comparing with a condition map which has only the key sets with id. Based on the condition map, I want to filter from the original map.
The original map which I have is,
Map<Integer, AppFeatureDTO> appFeatureMap = new TreeMap<>();
which will result like,
{
"101": {
"id": 101,
"subFeature": {
"1": {
"id": 1,
"title": "Title Value",
"desc": "Description Value"
}
}
},
"102": {
"id": 102,
"subFeature": {
"1": {
"id": 1,
"title": "Title Value",
"desc": "Description Value"
}
}
},
"103": {
"id": 103,
"subFeature": {
"1": {
"id": 1,
"title": "Title Value",
"desc": "Description Value"
},
"2": {
"id": 2,
"title": "Title Value",
"desc": "Description Value"
},
"3": {
"id": 3,
"title": "Title Value",
"desc": "Description Value"
},
"4": {
"id": 4,
"title": "Title Value",
"desc": "Description Value"
}
}
}
}
and the corresponding classes are:
class AppFeatureDTO {
private int id;
private Map<Integer, AppSubFeatureDTO> subFeature;
}
class AppSubFeatureDTO{
private int id;
private String title;
private String description;
}
then I have a filter map,
Map<Integer, FeatureDTO> conditionFilterMap = new TreeMap<>();
which is resulting like,
{
"101": {
"id": 101,
"subFeature": {
"1": {
"id": 1,
}
}
},
"103": {
"id": 103,
"subFeature": {
"2": {
"id": 2
},
"4": {
"id": 4
}
}
}
}
the corresponding classes for the filter map are,
class FeatureDTO {
private int id;
private Map<Integer, SubFeatureDTO> subFeature;
}
class SubFeatureDTO{
private int id;
}
I want to filter the result map using conditionFilterMap like,
{
"101": {
"id": 101,
"subFeature": {
"1": {
"id": 1,
"title": "Title Value",
"desc": "Description Value"
}
}
},
"103": {
"id": 103,
"subFeature": {
"2": {
"id": 2,
"title": "Title Value",
"desc": "Description Value"
},
"4": {
"id": 4,
"title": "Title Value",
"desc": "Description Value"
}
}
}
}
I'm using spring modelMapper to copy AppFeatureDTO to FeatureDTO. But, filtering the map, I didn't get clue.
Could you please suggest how to get the resultMap using Java 8?
Even I couldn't imagine a simple solution using Java 7 or 6 also.

Answer 1

Assuming that the map key is the same as the id field:
Map<Integer, AppFeatureDTO> resultMap = conditionFilterMap.values().stream()
.map(FeatureDTO::getId)
.map(appFeatureMap::get)
.collect(Collectors.toMap(AppFeatureDTO::getId, a -> new AppFeatureDTO(a.getId(),
conditionFilterMap.get(a.getId()).getSubFeature().values().stream()
.map(SubFeatureDTO::getId)
.map(a.getSubFeature()::get)
.collect(Collectors.toMap(AppSubFeatureDTO::getId, x -> x)))));
If you need TreeMap, add the arguments (a, b) -> a, TreeMap::new to the Collectors.toMap calls.
The non-stream version doesn't really look any worse:
Map<Integer, AppFeatureDTO> resultMap = new TreeMap<>();
for (FeatureDTO f : conditionFilterMap.values()) {
AppFeatureDTO a = appFeatureMap.get(f.getId());
Map<Integer, AppSubFeatureDTO> resultSub = new TreeMap<>();
for (SubFeatureDTO s : f.getSubFeature().values()) {
resultSub.put(s.getId(), a.getSubFeature().get(s.getId()));
}
resultMap.put(a.getId(), new AppFeatureDTO(a.getId(), resultSub));
}