stream流分组

前两天补充了博客中写的java8的stream的用法

今天再写个分组的

例如我们下面需要根据奇数偶数分组

可以先新建一个list

List<Integer> integerList = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 0));

然后进行分组

Map<Boolean, List<Integer>> collect = integerList.stream().collect(Collectors.groupingBy(data -> data % 2 == 0));
List<Integer> evenNumbers = collect.get(true);
List<Integer> oddNumber = collect.get(false);
System.out.println("data % 2 == 0-----------");
evenNumbers.forEach(System.out::println);
System.out.println("data % 2 != 0-----------");
oddNumber.forEach(System.out::println);

然后输出结果

比如我们现在自定义的User，我们需要根据username进行分组

List<User> userList = Lists.newArrayList();
userList.add(new User("ruben", "1"));
userList.add(new User("achao", "2"));
userList.add(new User("ruben", "3"));
Map<String, List<User>> userMap = userList.stream().collect(Collectors.groupingBy(User::getUsername));
List<User> ruben = userMap.get("ruben");
System.out.println("ruben-----------");
ruben.forEach(System.out::println);
List<User> achao = userMap.get("achao");
System.out.println("achao-----------");
achao.forEach(System.out::println);