stream进行分页

stream进行分页

说明:

最近看了一篇关于java8的StreamAPI使用的文章,正好看到一个和分页查询相关的api,由此写一个demo,加深对StreamAPI的印象

模拟dao层从数据库获取数据

实体类 User

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Integer id;
    private String name;
    private String address;
}

获取数据

public class UserDao {
    public List<User> findAll(){
        List<User> userList = new ArrayList<>(Arrays.asList(
                new User(1,"name","address"),
                new User(2,"name","address"),
                new User(3,"name","address"),
                new User(4,"name","address"),
                new User(5,"name","address"),
                new User(6,"name","address"),
                new User(7,"name","address"),
                new User(8,"name","address"),
                new User(9,"name","address"),
                new User(10,"name","address"),
                new User(11,"name","address"),
                new User(12,"name","address"),
                new User(13,"name","address"),
                new User(14,"name","address"),
                new User(15,"name","address"),
                new User(16,"name","address"),
                new User(17,"name","address"),
                new User(18,"name","address"),
                new User(19,"name","address"),
                new User(20,"name","address"),
                new User(21,"name","address"),
                new User(22,"name","")
        ));

        return  userList;
    }
}

模拟service层进行分页处理

public class UserService {
    public List<User> findUserByParamToPage(Integer index,Integer pageSize){
        UserDao userDao = new UserDao();
        List<User> users =
                userDao.findAll().stream()
                        /**
                         * 过滤address为""的数据
                         */
                        .filter(user -> !user.getAddress().equals(""))
                        /**
                         * 对数据进行id升序排序
                         */
                        .sorted((u1,u2)->u1.getId().compareTo(u2.getId())).collect(Collectors.toList());
                        /**
                         * 对过滤后的数据进行分页处理
                         */
        List<User> userPage = users.stream().skip((index - 1) * pageSize).limit(pageSize).collect(Collectors.toList());
        return userPage;
    }
}

测试

说明:

测试期间,我就是用main方法进行测试

为了验证分页功能成功,我们使用边界值,我们一共22条记录,去除一条address为""的记录,然后分页处理,查询第5页应该是一条数据为:

[User(id=21, name=name, address=address)]

public class App {
    public static void main(String[] args) {
        UserService userService = new UserService();
        List<User> users = userService.findUserByParamToPage(5, 5);
        System.out.println(users);
    }
}