7.排序(sorted)

sorted，中间操作。有两种排序：

• sorted()：自然排序，流中元素需实现Comparable接口
• sorted(Comparator com)：Comparator排序器自定义排序

List<User> userList1 = Arrays.asList(
        new User(1, "xw", "女", 22),
        new User(2, "zgx", "男", 21),
        new User(3, "whb", "男", 23),
        new User(4, "gg", "男", 30),
        new User(5, "yda", "男", 22),
        new User(6, "bhm", "女", 23),
        new User(7, "lsn", "女", 22),
        new User(8, "ksj", "女", 22)
);

// sorted
List<User> userList2 = userList1.stream()
        .sorted(Comparator.comparing(User::getAge))
        .collect(Collectors.toList());
log.info(String.format("按照年龄排序，结果为：%s", userList2));

// 从小到大，正序
List<String> userName1 = userList1.stream()
        .sorted(Comparator.comparing(User::getAge))
        .map(User::getName)
        .collect(Collectors.toList());
log.info(String.format("根据年龄从小到大排序：%s", userName1));

// 从大到小，倒序
List<String> userName2 = userList1.stream()
        .filter(user -> user.getSex().equals("男"))
        .sorted(Comparator.comparing(User::getAge).reversed())
        .map(User::getName)
        .collect(Collectors.toList());
log.info(String.format("男用户根据年龄从大到小排序：%s", userName2));

8.提取/组合

流也可以进行合并、去重、限制、跳过等操作。

1.去重排序

List<Integer> list = Arrays.asList(1, 2, 4, 4, 10, 9, 6, 8, 6, 2, 3, 7, 5);
List<Integer> collect = list
        .stream()
        .distinct()
        .sorted(Comparator.comparing(Integer::intValue))
        .collect(Collectors.toList());
collect.forEach(x -> System.out.print(x+" ")); // 1 2 3 4 5 6 7 8 9 10

存在重复数据的问题，这里使用stream流的衍生功能，去除一个对象中的部分元素的重复如下：

List<User> userList = Arrays.asList(
        new User(1, "xw", "女", 21),
        new User(2, "zgx", "男", 21),
        new User(3, "whb", "男", 23),
        new User(4, "gag", "男", 30),
        new User(4, "gbg", "男", 30),
        new User(4, "gcg", "女", 30),
        new User(5, "yda", "男", 22),
        new User(6, "bhm", "女", 23),
        new User(7, "lsn", "女", 22),
        new User(8, "ksj", "女", 22)
);
ArrayList<User> collect1 = userList.stream().collect(Collectors.collectingAndThen(
                        Collectors.toCollection(() -> new TreeSet<>(
                                Comparator.comparing(
                                        User::getId))), ArrayList::new));

多个字段或者多个条件去重

ArrayList<User> collect2 = userList.stream().collect(Collectors.collectingAndThen(
                Collectors.toCollection(() -> new TreeSet<>(
                        Comparator.comparing(user->user.getName() + ";" + user.getId()))), ArrayList::new)