[보완] stream으로 리팩토링하기

[Catnap421]

dnd-5th-5-backend/src/main/java/com/meme/ala/domain/alacard/service/AlaCardServiceImpl.java

Line 141 in 20aba2d

public Map<String, List<BackgroundDtoInSetting>> getBackgroundThumbCategory() {

dnd-5th-5-backend/src/main/java/com/meme/ala/domain/aggregation/service/AggregationServiceImpl.java

Line 77 in 20aba2d

public void submitWordList(Member member, Aggregation aggregation, List<String> wordIdList) throws UnsupportedEncodingException {

dnd-5th-5-backend/src/main/java/com/meme/ala/domain/aggregation/service/AggregationServiceImpl.java

Line 99 in 20aba2d

private Map<String, LinkedList<String>> dtoListToMapByMiddleCategory(List<String> wordIdList) throws UnsupportedEncodingException {