Java8 Stream流 flatMap使用

news2024/9/24 19:22:55

参考链接

import cn.hutool.core.collection.ListUtil;
import lombok.AllArgsConstructor;
import lombok.Data;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class FlatMapLearn {
    @Data
    @AllArgsConstructor
    public static class User {
        /** 姓名 */
        private String name;

        /** 权限 */
        private List<String> permissionList;
    }

    public static void main(String[] args) {
        // 创建5个用户
        List<User> users = new ArrayList<>();
        users.add(new User("Alice", ListUtil.of("A", "B", "C")));
        users.add(new User("Bob", ListUtil.of("B", "C", "D")));
        users.add(new User("Charlie", ListUtil.of("C", "D", "E")));
        users.add(new User("David", ListUtil.of("D", "E", "F")));
        users.add(new User("Eve", ListUtil.of("E", "F", "G")));

        // 使用map获取
        List<String> list = new ArrayList<>();
        users.stream().map(User::getPermissionList).forEach(l -> {
            l.stream().forEach(str -> {
                if (!list.contains(str)) {
                    list.add(str);
                }
            });
        });
        System.out.println(list);


        // 使用map和flatmap获取他们所有的权限
        List<String> allPermissions = users.stream()
                .flatMap(user -> user.getPermissionList().stream())
                .distinct()
                .collect(Collectors.toList());

        // 输出结果
        System.out.println(allPermissions);
    }
}