调用/users/register接口时，JPA保存User出现实体未识别错误

我通过POST请求调用/users/register接口，请求体如下：

{
    "username": "daniel",
    "email": "email@yahoo.com",
    "password": "something"
}

调用后触发500内部服务器错误，核心错误信息：

{
    "timestamp": "2023-03-08T05:40:40.215+00:00",
    "status": 500,
    "error": "Internal Server Error",
    "message": "com.youngahn.RobinhoodAPI.controllers.UserController$1 is not an entity",
    "path": "/users/register"
}

相关代码如下：

User实体类 #

package com.youngahn.RobinhoodAPI.entity;

import jakarta.persistence.*;
import jakarta.validation.constraints.NotBlank;
import lombok.Data;

import java.math.BigDecimal;
import java.util.HashSet;
import java.util.Set;

@Entity
@Table(name = "users")
@Data
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotBlank
    private String username;

    @NotBlank
    private String email;

    @NotBlank
    private String password;

    private BigDecimal funds = new BigDecimal("0.00");

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "user")
    public Set<UserStock> userStocks = new HashSet<>();

}

UserController控制器类 #

package com.youngahn.RobinhoodAPI.controllers;

import com.youngahn.RobinhoodAPI.dtos.LoginRequestDto;
import com.youngahn.RobinhoodAPI.dtos.RegisterRequestDto;
import com.youngahn.RobinhoodAPI.entity.User;
import com.youngahn.RobinhoodAPI.repository.UserRepository;
import jakarta.validation.Valid;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/users")
@CrossOrigin(origins = "*")
public class UserController {
    private UserRepository userRepository;

    @Autowired
    public UserController(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    @PostMapping("/signin")
    public ResponseEntity<?> getUser(@RequestBody LoginRequestDto loginRequestDto) {
        return ResponseEntity.ok(loginRequestDto);
    }

    @PostMapping("/register")
    public ResponseEntity<?> createUser(@Valid @RequestBody RegisterRequestDto registerRequestDto) {
        User user = new User() {{
            setUsername(registerRequestDto.getUsername());
            setEmail(registerRequestDto.getEmail());
            setPassword(registerRequestDto.getPassword());
        }};

        userRepository.save(user);
        return ResponseEntity.ok(registerRequestDto);
    }
}

UserRepository仓库类 #

package com.youngahn.RobinhoodAPI.repository;

import com.youngahn.RobinhoodAPI.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    
}

问题原因 #

你用了**双重初始化（匿名内部类）**的方式创建User对象：

User user = new User() {{
    setUsername(registerRequestDto.getUsername());
    // ...
}};

这种写法会生成一个User的匿名子类（也就是错误里的UserController$1），但JPA只能识别标注了@Entity的原始实体类，无法识别这个动态生成的子类，因此抛出"not an entity"错误。

修复方案 #

换成常规的对象初始化方式即可：

@PostMapping("/register")
public ResponseEntity<?> createUser(@Valid @RequestBody RegisterRequestDto registerRequestDto) {
    User user = new User();
    user.setUsername(registerRequestDto.getUsername());
    user.setEmail(registerRequestDto.getEmail());
    user.setPassword(registerRequestDto.getPassword());

    userRepository.save(user);
    return ResponseEntity.ok(registerRequestDto);
}

如果想让代码更简洁，可以给User类加上Lombok的@Builder注解：

1. 修改User实体类：

@Entity
@Table(name = "users")
@Data
@Builder
public class User {
    // 原有代码不变
}

2. 在Controller中使用Builder创建对象：

User user = User.builder()
        .username(registerRequestDto.getUsername())
        .email(registerRequestDto.getEmail())
        .password(registerRequestDto.getPassword())
        .build();

额外提醒 #

• 密码不要明文存储，建议用BCrypt等加密工具处理后再保存。
• 可以添加用户名/邮箱的唯一性校验，避免重复注册。

内容的提问来源于stack exchange，提问作者Danii