1 拼接集合中的字符串
String allStr = courseList.stream().map(e -> e.getTitle()).collect(Collectors.joining());
2 集合中数字求和
double totalDuration = courseList.stream().mapToDouble(d -> Double.valueOf(d.getDuration())).sum();
3 集合中的字段构造成数组
List<Integer> questionIdList = questionList.stream().map(Question::getId).collect(Collectors.toList());
4 filter过滤&集合中的字段构造成map数组
List<Map<String, Object> remoteMapData = new ArrayList<>();
List<Map<String, Object>> finalRemoteData = remoteMapData.stream().filter(r -> !r.get("user_id").equals(CategoryType.ADMIN_DOWN_ID)).map(r -> {
Map<String, Object> mapR = new HashMap<>();
mapR.put("portId", r.get("_id"));
mapR.put("portAuthor", r.get("user"));
return mapR;
}).collect(Collectors.toList());
5 构造指定值的数组并遍历
Stream.of("1", "2", "3").forEach(System.out::println);
