无法构造“com.domain.User”的实例（不存在创建者，如默认构造函数）：无法从对象值反序列化

Question

ObjectNode我有一个接受as 的控制器@RequestBody。

这ObjectNode代表json一些用户数据

{
    "given_name":"ana",
    "family_name": "fabry",
    "email": "fabry@gmail.com",
    "password": "mypass",
    "gender": "FEMALE"
}

控制器.java

@PostMapping(produces = MediaType.APPLICATION_JSON_VALUE)
    public JsonNode createUser(@RequestBody ObjectNode user){
        return userService.addUser(user);
 }

我想让用户将ObjectNode其转换为 JavaPOJO将其保存到数据库并再次将其返回为JsonNode.

UserServiceImpl.java

    private final UserRepository userRepository;
    private final UserMapper userMapper;

    @Override
    public JsonNode addUser(@RequestBody ObjectNode user) {
        try {
            return userMapper.fromJson(user)
                    .map(r -> {
                        final User created = userRepository.save(r);
                        return created;
                    })
                    .map(userMapper::toJson)
                    .orElseThrow(() -> new ResourceNotFoundException("Unable to find user"));
        } catch (RuntimeException re) {
            throw re;
        }
    }

转换ObjectNode为POJO

我在UserMapper课堂上这样做了：

public Optional<User> fromJson(ObjectNode jsonUser) {
  User user = objectMapper.treeToValue(jsonUser, User.class);
}

另外，要写入对象，JsonNode我这样做了：

public JsonNode toJson(User user) {
        ObjectNode node = objectMapper.createObjectNode();
        node.put("email", user.email);
        node.put("password", user.password);
        node.put("firstName", user.firstName);
        node.put("lastName", user.firstName);
        node.put("gender", user.gender.value);
        node.put("registrationTime", user.registrationTime.toString());
        return node;
}

用户.java

@Document(collection = "user")
@Builder
@AllArgsConstructor
public class User {

    @Indexed(unique = true)
    public final String email;
    @JsonProperty("password")
    public final String password;
    @JsonProperty("firstName")
    public final String firstName;
    @JsonProperty("lastName")
    public final String lastName;
    @JsonProperty("gender")
    public final Gender gender;
    @JsonProperty("registrationTime")
    public final Instant registrationTime;

    public static User createUser(
            String email,
            String password,
            String firstName,
            String lastName,
            Gender gender,
            Instant registrationTime){
        return new User(email, password, firstName, lastName, gender, registrationTime);
    }
}

当我运行我的应用程序时，这是我收到的错误：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.domain.User` (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

我已阅读有关该错误的信息，似乎发生此错误是因为 Jackson 库不知道如何创建一个没有空构造函数的模型，并且该模型包含一个带有参数的构造函数，我用 注释了其参数@JsonProperty("fieldName")。但即使在申请后@JsonProperty("fieldName")我仍然遇到同样的错误。

我已将 ObjecatMapper 定义为 Bean

    @Bean
    ObjectMapper getObjectMapper(){
        return new ObjectMapper();
    }

我在这里缺少什么？

Answer 1

我可以重现该异常。然后我添加了一个全参数构造函数，每个参数都用 right 注释@JsonProperty。

@JsonCreator
public User( 
    @JsonProperty("email") String email,
    @JsonProperty("password") String password,
    @JsonProperty("firstName") String firstName,
    @JsonProperty("lastName") String lastName,
    @JsonProperty("gender") String gender,
    @JsonProperty("registrationTime") Instant registrationTime){
            super();
            this.email = email;
            this.password = password;
            this.firstName = firstName;
            this.lastName = lastName;
            this.gender = gender;
            this.registrationTime = registrationTime;
}

现在，它创建了实例，但我收到其他映射错误（无法识别的字段“given_name”），您应该能够解决这些错误。