Collector接口

java.util.stream.Collector

存在4个方法，分别是

举例实现1

  • toList ``` 1、创建集合 ArrayList::new 2、数据添加到容中(技术数据到容器中) List::add 3、合并2个数据到一个并返回 (left, right) -> { left.addAll(right); return left;} 4、返回最终数据 i -> (R) i

结合起来就是 public static Collector> toList() { return new CollectorImpl<>((Supplier>) ArrayList::new, List::add, (left, right) -> { left.addAll(right); return left; }, CH_ID); }

  2. <a name="LUU1z"></a>
  3. #### 举例实现2
  4. ```java
  5. //---生成数据
  6. final List<Project> collect = IntStream.range(0, 10)
  7.         .mapToObj(x -> new Project(x, "projectName" + x))
  8.         .collect(Collectors.toList());
  9. //---操作
  10. final List<String> categorys = Arrays.asList("projectName1", "projectName2");
  11.  //--针对项目名字进行分组
  12. final Map<String, List<Project>> map = collect.
  13.         stream()
  14.         .filter(x -> StringUtils.isNotBlank(x.getProjectName()))
  15.         .filter(x -> categorys.contains(x.getProjectName()))
  16.         .collect(Collectors.groupingBy(Project::getProjectName));
  17.  //-- 分组后进行转换
  18. final List<Project> collect1 = categorys.stream()
  19.         .filter(map::containsKey)
  20.         .flatMap(x -> map.getOrDefault(x, new ArrayList<>()).stream())
  21.         .collect(new Ff());
  22. System.out.println(JSONObject.toJSONString(collect1));
  23. //--
  24. class Ff implements Collector<Project, Set<String>, List<Project>> {
  26.     private final List<Project> projects = new ArrayList<>();
  28.     @Override
  29.     public Supplier<Set<String>> supplier() {
  30.         return HashSet::new;
  31.     }
  33.     @Override
  34.     public BiConsumer<Set<String>, Project> accumulator() {
  35.         return (x, i) -> {
  36.             if (x.add(i.getProjectName())) {
  37.                 projects.add(i);
  38.             }
  39.         };
  40.     }
  42.     @Override
  43.     public BinaryOperator<Set<String>> combiner() {
  44.         return (integers, integers2) -> {
  45.             integers.addAll(integers2);
  46.             return integers;
  47.         };
  48.     }
  50.     @Override
  51.     public Function<Set<String>, List<Project>> finisher() {
  52.         return strings -> projects;
  53.     }
  55.     @Override
  56.     public Set<Characteristics> characteristics() {
  57.         return Collections.unmodifiableSet(EnumSet.of(Characteristics.CONCURRENT));
  58.     }
  59. }