How do I extract a list of Objects from a java stream? - java-8

Question

Note that there are 3 levels of nesting here -
I am trying to retrieve a list of filters from a filtersubgroup list which is in a filtersupergroup list.
the filter has a property - fieldname.
I managed to extract the list of field names from the data structure using the following method :
public static List<String> extractFilterFieldsAsAList(QuerySearchRequestDTO requestDTO) {
return requestDTO.getFilter().parallelStream()
.map(new Function<FilterSuperGroup, String>() {
#Override
public String apply(FilterSuperGroup filterSuperGroup) {
return filterSuperGroup.getFilterSubGroup().parallelStream()
.map(new Function<FilterSubGroup, String>() {
#Override
public String apply(FilterSubGroup filterSubGroup) {
return filterSubGroup.getFilter().parallelStream()
.map(new Function<Filter, String>() {
#Override
public String apply(Filter t) {
// TODO Auto-generated method stub
return t.getFieldName();
}
}).collect(Collectors.joining(" "));
}
}).collect(Collectors.joining(" "));
}
}).collect(Collectors.toList());
}
Question: However, in another scenario (BELOW) I need a List as the output.
I want to replace findAny().get() with something that doesn't break the stream nesting. findAny().get() is obviously incorrect as it returns only one element from each nest. How do I fix this?
public static List<Filter> prepareFilterListFromRequest(QuerySearchRequestDTO requestDTO) {
List<Filter> listToReturn = new ArrayList<>();
listToReturn.addAll(requestDTO.getFilter().stream()
.map(new Function<FilterSuperGroup, List<Filter>>() {
#Override
public List<Filter> apply(FilterSuperGroup filterSuperGroup) {
return filterSuperGroup.getFilterSubGroup().parallelStream()
.map(new Function<FilterSubGroup, Filter>() {
#Override
public Filter apply(FilterSubGroup filterSubGroup) {
// TODO Auto-generated method stub
return filterSubGroup.getFilter().stream()
.map(new Function<Filter, Filter>() {
#Override
public Filter apply(Filter t) {
// TODO Auto-generated method stub
return t;
}
}).findAny().get();
}
}).collect(Collectors.toList());
}
}).findAny().get()
);
return listToReturn;
}