java - 杰克逊自定义反序列化器在 Spring Boot 中不起作用
问题描述
我为我的实体创建了一个自定义反序列化器,但它不断抛出异常:
我有两个类:AppUser 和 AppUserAvatar
应用用户.java
@Entity
@Table(name = "user")
public class AppUser implements Serializable {
@Transient
private static final long serialVersionUID = -3536455219051825651L;
@JsonProperty(access = JsonProperty.Access.WRITE_ONLY)
@Column(name = "password", nullable = false, length = 256)
private String password;
@JsonIgnore
@Column(name = "is_active", nullable = false)
private boolean active;
@JsonIgnore
@OneToMany(mappedBy = "appUser", targetEntity = AppUserAvatar.class, fetch = FetchType.LAZY)
private List<AppUserAvatar> appUserAvatars;
//// Getters and Setters and toString() ////
}
AppUserAvatar.java
@Entity
@Table(name = "user_avatar")
public class AppUserAvatar extends BaseEntityD implements Serializable {
@Transient
private static final long serialVersionUID = 8992425872747011681L;
@Column(name = "avatar", nullable = false)
@Digits(integer = 20, fraction = 0)
@NotEmpty
private Long avatar;
@JsonDeserialize(using = AppUserDeserializer.class)
@JsonProperty(access = JsonProperty.Access.WRITE_ONLY)
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "user_id", nullable = false)
private AppUser appUser;
//// Getters and Setters and toString() ////
}
AppUserDeserializer.java 包 com.nk.accountservice.deserializer;
import com.edoctar.accountservice.config.exception.InputNotFoundException;
import com.edoctar.accountservice.domain.candidate.AppUser;
import com.edoctar.accountservice.service.candidate.AppUserService;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;
import org.springframework.beans.factory.annotation.Autowired;
import java.io.IOException;
import java.io.Serializable;
public class AppUserDeserializer extends JsonDeserializer implements Serializable {
private static final long serialVersionUID = -9012464195937554378L;
private AppUserService appUserService;
@Autowired
public void setAppUserService(AppUserService appUserService) {
this.appUserService = appUserService;
}
@Override
public Object deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
JsonNode node = jsonParser.getCodec().readTree(jsonParser);
Long userId = node.asLong();
System.out.println(node);
System.out.println(node.asLong());
AppUser appUser = appUserService.findById(userId);
System.out.println("appuser: " + appUser);
if (appUser == null) try {
throw new InputNotFoundException("User not found!");
} catch (InputNotFoundException e) {
e.printStackTrace();
return null;
}
return appUser;
}
}
示例 xhr 男孩是:
{
"appUser": 1,
"avatar": 1
}
每次我提交请求时都会引发异常。
Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: (was java.lang.NullPointerException); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.edoctar.accountservice.domain.candidate.AppUserAvatar["appUser"])]
我发现 appUserService.findById() 方法没有被调用。我真的很困惑。我不知道我哪里错了。对于任何解决方案都将非常有用。谢谢。
解决方案
更新的答案:
您不能使用自动装配属性,因为您不在 Spring 上下文中。您正在将类AppUserDeserializer
作为注释中的引用 传递
@JsonDeserialize(using = AppUserDeserializer.class)
在这种情况下是创建 的实例的FasterJacksonAppUserDeserializer
库,因此Autowired
不考虑注释。
你可以用一个小技巧来解决你的问题。在以下位置添加对 spring 创建的实例的静态引用AppUserService
:
@Service
public AppUserService {
public static AppUserService instance;
public AppUserService() {
// Modify the constructor setting a static variable holding a
// reference to the instance created by spring
AppUserService.instance = this;
}
...
}
使用该参考AppUserDeserializer
:
public class AppUserDeserializer extends JsonDeserializer implements Serializable {
private AppUserService appUserService;
public AppUserDeserializer() {
// Set appUserService to the instance created by spring
this.appUserService = AppUserService.instance;
}
...
}
原始答案:要正确初始化Autowired
属性,您必须注释您的 class AppUserDeserializer
,否则appUserService
如果您没有使用 set 方法显式初始化它,则为 null 。
尝试使用AppUserDeserializer
注释@Component
:
@Component // Add this annotation
public class AppUserDeserializer extends JsonDeserializer implements Serializable {
...
}
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