JAVA - Stream API List Map 을 원하는 값으로 groupingBy 하기

companyNo를 기준으로 groupingBy

List<HashMap<String, Object>> stringList = new ArrayList<>();

stringList.add(new HashMap<String, Object>(){{
	put("companyNo", 1);
	put("email", "aaa@gmail.com");
}});
stringList.add(new HashMap<String, Object>(){{
	put("companyNo", 3);
	put("email", "bbb@gmail.com");
}});
stringList.add(new HashMap<String, Object>(){{
	put("companyNo", 5);
	put("email", "ccc@gmail.com");
}});
stringList.add(new HashMap<String, Object>(){{
	put("companyNo", 1);
	put("email", "ddd@gmail.com");
}});

>> 데이터 형태

[{companyNo=1, email=aaa@gmail.com}, {companyNo=3, email=bbb@gmail.com}, {companyNo=5, email=ccc@gmail.com}, {companyNo=1, email=ddd@gmail.com}]

 

Map<Integer, List<HashMap<String, Object>>> s = stringList.stream().collect(Collectors.groupingBy(m -> Integer.parseInt(m.get("companyNo").toString()), HashMap::new, Collectors.toList()));

 

>> 결과

{1=[{companyNo=1, email=aaa@gmail.com}, {companyNo=1, email=ddd@gmail.com}], 3=[{companyNo=3, email=bbb@gmail.com}], 5=[{companyNo=5, email=ccc@gmail.com}]}

 

 

HashMap<Integer, List<String>> userList = new HashMap<>();
			map.entrySet().stream().forEach(m -> userList.put(m.getKey(), m.getValue().stream().map(s -> s.get("email").toString()).collect(Collectors.toList())));

 

>> 결과

{1=[aaa@gmail.com, ddd@gmail.com], 3=[bbb@gmail.com], 5=[ccc@gmail.com]}