Stream流转map用法

最新推荐文章于 2025-01-06 17:33:34 发布

原创最新推荐文章于 2025-01-06 17:33:34 发布 · 1.2k 阅读

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这篇博客展示了如何使用Java集合框架中的Stream API进行数据处理。通过创建一个User对象列表，然后分别使用groupingBy、toMap方法进行分组和映射操作，展示了不同场景下的Stream API用法。示例中包括了根据userId分组和根据userId、username生成不同类型的Map。

List<User> users = new ArrayList<>();
users.add(new User(4L,"liuliu"));
users.add(new User(1L,"zhangsan"));
users.add(new User(3L,"wangwu"));
users.add(new User(2L,"lisi"));

Map map4 = users.stream().collect(Collectors.groupingBy(User::getUserId));

Map map1 = users.stream().collect(Collectors.toMap(User::getUserId,
        Function.identity(), (x, y) -> x));

Map map2 = users.stream().collect(Collectors.toMap(User::getUserId,
        User::getUsername, (x, y) -> x));

Map map3 = users.stream().sorted(Comparator.comparingLong(User::getUserId)).collect(Collectors.groupingBy(User::getUserId));

System.out.println(map1);
System.out.println(map2);
System.out.println(map3);
System.out.println(map4);

class User{
    private Long userId;

    private String username;

    public long getUserId() {
        return userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public User(Long userId, String username) {
        this.userId = userId;
        this.username = username;
    }

    public User() {
    }

}