java8 之 lambada stream使用方法

本文主要是介绍java8 之 lambada stream使用方法，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

stream 常用方法

取 List arr 指定key 并用逗号隔开,外加判断条件过滤

arr.filter(Objects::nonNull).stream().map(entity->entity.getCode() == 100 ? entity.key() "").filter(StringUtils::isNoneBlank).collect(Collectors.joining(",")

过滤掉 map value 为空 or null 的属性

        Map<String, Object> map1 = Optional.ofNullable(map).map((v) -> {Map params = v.entrySet().stream().filter((e) -> (e.getValue()==null||e.getValue().equals("") ? false : true)).collect(Collectors.toMap((e) -> (String) e.getKey(),(e) -> e.getValue()));return params;}).orElse(null);

List 根据指定字段去重

List<NeusoftPatientInfo> newList = patientInfos.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(NeusoftPatientInfo::getIdentityCard))), ArrayList::new));

List<Entity>转 List<Map>

public Map<String, Object> toMap(NeusoftMedicineInfo medicineInfo) {Map<String, Object> map = Maps.newHashMap();map.put("beginTime", medicineInfo.getBeginTime());map.put("identityCard", medicineInfo.getIdentityCard());map.put("drugName", medicineInfo.getDrugName());map.put("dosages", medicineInfo.getDosages());map.put("unit", medicineInfo.getUnit());map.put("dosagesSum", medicineInfo.getDosagesSum());map.put("unitSum", medicineInfo.getUnitSum());map.put("methods", medicineInfo.getMethods());map.put("frequency", medicineInfo.getFrequency());return map;
}List<Map<String, Object>> collect = medicineInfos.stream().map(medicineInfo -> medicineInfo.toMap(medicineInfo)).collect(Collectors.toList());

复杂例子将list 按某一字段分组后,映射成指定map 类型

Map<String, Map<String, Object>> collect = list.stream().map(neusoftRecordsInfo -> neusoftRecordsInfo.toMap(neusoftRecordsInfo)).filter(Objects::nonNull).collect(Collectors.groupingBy(e -> e.get("id").toString(), Collectors.toMap((e) -> e.keySet().stream().reduce((first, second) -> first).get(),(f) -> f.entrySet().stream().reduce((first, second) -> first).get().getValue(), (v1, v2) -> v2)));public Map<String, Object> toMap(NeusoftRecordsInfo recordsInfo) {Map<String, Object> map = Maps.newLinkedHashMap();String c = recordsInfo.itemcode;String r = recordsInfo.getResult();if ("HGB".equals(c)) {map.put("hemoglobin", r);}if ("WBC".equals(c)) {map.put("leukocyte", r);}if ("PLT".equals(c)) {map.put("platelet", r);}if (map.keySet().isEmpty()) {return null;}map.put("id", recordsInfo.getBarcode());return map;

复杂例子将list 某些条件分组,并排序,归纳子集某一字段组成list

        Map<String, List<String>> collect = lists.stream().collect(Collectors.groupingBy(e -> StringUtils.substringBefore(e.getRecordDate(), " "),TreeMap::new, Collectors.mapping(MgDataEntity::getMachineBloodSugar, Collectors.toList())));

分组,并排序,归纳子集某一字段取 entity

        Map<Integer, IotDataFoundation> collect = iotDataFoundations.stream().filter(Objects::nonNull).collect(Collectors.toMap(IotDataFoundation::getMonType, Function.identity(), BinaryOperator.maxBy(Comparator.comparing(IotDataFoundation::getId))));