当前位置：首页 > article >正文

@Builder用法

article 2025/2/6 4:01:40

一.场景模拟@Data两个缺点

假如有一结果api结果返回值的类Result，其在代码中频繁被使用：

@Data
public class Result<T> {
    private int code;
    private String message;
    private T data;

    public Result(int code, String message, T data) {
        this.code = code;
        this.message = message;
        this.data = data;
    }
}

如果要使用它，一般的方法是：

public class Main {
    public static void main(String[] args) {
        //方法1，使用全量的构造函数
        User result1 = new User( "你", "好");

        //方法2，使用空的构造函数加setter函数赋值
        User user = new User();
        user.setUsername("你");
        user.setPassword("好");
    }
}

这两种使用方法的弊端有：

（1）方法一：当只需要部分参数的时候需要再定义个构造函数（比如只要username,不要password），且一旦参数较多，则构造函数冗长；

（2）方法二：setter冗长；

因此我们需要builder来解决这个问题

二.java实现@`builder`

@Builder
public class User {
    private final Integer code = 200;
    private String username;
    private String password;
}

// 编译后：
public class User {
    private String username;
    private String password;
    User(String username, String password) {
        this.username = username; this.password = password;
    }
    public static User.UserBuilder builder() {
        return new User.UserBuilder();
    }

    public static class UserBuilder {
        private String username;
        private String password;
        UserBuilder() {}

        public User.UserBuilder username(String username) {
            this.username = username;
            return this;
        }
        public User.UserBuilder password(String password) {
            this.password = password;
            return this;
        }
        public User build() {
            return new User(this.username, this.password);
        }
        public String toString() {
            return "User.UserBuilder(username=" + this.username + ", password=" + this.password + ")";
        }
    }
}

    public static void main(String[] args) {
        User user = User.builder()
                .username("ni")
                .password("44")
                .build();
        System.out.println(user);
        //User(code=200, username=ni, password=44)
    }