Java新特性玩转JDK8之流操作map和filter函数

map函数

功能详情 将流中的每一个元素 T 映射为 R（类似类型转换）

使用场景 转换对象，如javaweb开发中集合里面的DO对象转换为DTO对象

示例 当前端需要展示所有用户时，要避免返回过多信息，并防止暴漏数据库其他字段。 定义User类，该类属性和数据库字段一 一对应。（id，用户名，密码）

public class User {
          
   

    private int id;

    private String name;

    private String pwd;

    public User(){
          
   

    }

    public  User(int id, String name,String pwd){
          
   
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }


    public int getId() {
          
   
        return id;
    }

    public void setId(int id) {
          
   
        this.id = id;
    }

    public String getName() {
          
   
        return name;
    }

    public void setName(String name) {
          
   
        this.name = name;
    }

    public String getPwd() {
          
   
        return pwd;
    }

    public void setPwd(String pwd) {
          
   
        this.pwd = pwd;
    }
}

- 定义UserDTO类，该类中属性为 前端需要展示的字段。（id，用户名）

public class UserDTO {
          
   

    private int userId;

    private String username;


    public UserDTO(){
          
   }

    public UserDTO(int userId, String username){
          
   
        this.userId = userId;
        this.username = username;
    }


    public int getUserId() {
          
   
        return userId;
    }

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

    public String getUsername() {
          
   
        return username;
    }

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

    @Override
    public String toString() {
          
   
        return "UserDTO{" +
                "userId=" + userId +
                ", username=" + username +  +
                };
    }
}

- 主程序（将多余的 密码 属性清理掉）

public class Main {
          
   
    public static void main(String[] args) {
          
   
        List<User> list = Arrays.asList(new User(1,"小东","123"),new User(21,"jack","rawer"),
                new User(155,"tom","sadfsdfsdfsd"),
                new User(231,"marry","234324"),new User(100,"小D","122223"));
        List<UserDTO> userDTOList = list.stream().map(obj->{
          
   
            UserDTO userDTO = new UserDTO(obj.getId(),obj.getName());
            return userDTO;
        }).collect(Collectors.toList());
        System.out.println(userDTOList);
    }
}

filter函数

功能详情 过滤出流中符合条件的元素

示例 过滤出LIst中元素长度大于5的 元素 主程序

public class Main {
          
   
    public static void main(String[] args) {
          
   
        List<String> list = Arrays.asList("springboot", "springcloud", "redis", "git", "netty", "java", "html", "docker");

        List<String> resultList = list.stream().filter(obj -> obj.length() > 5).collect(Collectors.toList());

        System.out.println(resultList);
        // 打印 [springboot, springcloud, docker]
    }
}