Stream

转集合

List<String> strList=list.stream.map(T::get).collect(Collectors.toList);

根据分类分组

List<AppModel> list=new ArrayList<>();
Map<String, List<AppModel>> groupByCategoryList = appModelList
    .stream()
    .collect(
    Collectors
    .groupingBy(AppModel::getModelCategory)
);

分组后数据排序

Map<String, List<AppModel>> groupAppMap = new HashMap<>(50);
Map<String, List<AppModel>> groupByCategoryList
groupByCategoryList.forEach((s, appModels) -> {
    List<AppModel> collect = appModels.stream()
        .filter(appModel -> appModel.getSort() != null)
        .sorted(Comparator.comparing(BaseEntity::getSort))
        .collect(Collectors.toList());
    groupAppMap.put(s, collect);
});

按照分类顺序获取数据

List<Map<String, Object>> categoryList;
categoryList.forEach(stringObjectMap -> {
    String id = String.valueOf(stringObjectMap.get("id"));
    String name = String.valueOf(stringObjectMap.get("name"));
    String icon = String.valueOf(stringObjectMap.get("icon"));
    List<AppModel> appModels = groupAppMap.get(id);
    LinkedHashMap<String, Object> hashMap = new LinkedHashMap<>();
    hashMap.put("name", name);
    hashMap.put("icon", icon);
    hashMap.put("apps", appModels);
    linkedList.add(hashMap);
	}
);

过滤

List<String> idList;
idList.stream().map(this::getById).filter(Objects::nonNull).forEach(docNo -> {
//执行操作
});

getById 是调用方法获取一个对象

去重

List<String> appIds = list.stream().distinct().collect(Collectors.toList());

重组Map

Map<String,String> map=historicProcessInstanceList
    .stream()
    .collect(Collectors.toMap(HistoricProcessInstance::getId,HistoricProcessInstance::getBusinessKey);