springboot注册

查询用户，判断用户名是否被占用。

1.没有被占用，则注册

2.被占用，则显示用户名已被占用！

service : UserService

import com.example.pojo.User;

public interface UserService {
    //根据用户名查询用户
    User findByUserName(String username);
}

mapper : UserMapper

@Mapper
public interface UserMapper {
    //根据用户名查询用户
    @Select("select * from user where username=#{username}")
    User findByUserName(String username);
}

controller : UserController

import com.example.pojo.Result;
import com.example.pojo.User;
import com.example.service.UserService;
import jakarta.validation.constraints.Pattern;
import org.springframework.beans.factory.annotation.Autowired;

@RestController
@RequestMapping("/user")
@Validated
public class UserController {
    @Autowired
    private UserService userService;
    @PostMapping("/register")
    public Result register(@Pattern(regexp = "^\\S{5,16}$") String username, @Pattern(regexp = "^\\S(5,16)$") String password) {
        //查询用户
        User user = userService.findByUserName(username);
        if(user == null){
            //没有占用，注册
            userService.register(username,password);
            return Result.success();
        }else {
            //占用
            return Result.error("用户名已被占用！");
        }
    }
}