POJO与DTO转换

通用DTO泛型接口

public interface DTOConvert<S,T>{
    public T convert(S s);
}

public class UserDTOConvert implements DTOConvert {
    @Override
    public User convert(UserDTO userDTO) {
        BeanUtils.copyProperties(source,target);
        return target;
    }
}

二级封装

public class UserInputDTO {
	private String username;
    
	private int age;
	//get and set
    public User convertToUser(){
        UserInputDTOConvert userInputDTOConvert = new UserInputDTOConvert();
        User convert = userInputDTOConvert.convert(this);
        return convert;
    }

    private static class UserInputDTOConvert implements DTOConvert<UserInputDTO,User> {
        @Override
        public User convert(UserInputDTO userInputDTO) {
            User user = new User();
            BeanUtils.copyProperties(userInputDTO,user);
            return user;
        }
    }
}

继承guava的抽象类Covert<A,B> ，完成正向转换和逆向转换

public class UserDTO {
    private String username;
    private int age;
	//getter and setter
    public User convertToUser(){
            UserDTOConvert userDTOConvert = new UserDTOConvert();
            User convert = userDTOConvert.convert(this);
            return convert;
    }

    public UserDTO convertFor(User user){
            UserDTOConvert userDTOConvert = new UserDTOConvert();
            UserDTO convert = userDTOConvert.reverse().convert(user);
            return convert;
    }

    private static class UserDTOConvert extends Converter<UserDTO, User> {
            @Override
            protected User doForward(UserDTO userDTO) {
                    User user = new User();
                    BeanUtils.copyProperties(userDTO,user);
                    return user;
            }

            @Override
            protected UserDTO doBackward(User user) {
                    UserDTO userDTO = new UserDTO();
                    BeanUtils.copyProperties(user,userDTO);
                    return userDTO;
            }
    }

}

转换Util可以参考网络上的性能测试与实际结合选择：
文章：https://www.javazhiyin.com/81344.html

后起之秀还有MapStruct，可以了解下。