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问题描述
我正在尝试使用 Jackson 在 JSON 有效载荷以下反序列化：
I'm trying to deserialise below JSON payload with Jackson:
{"code":null,"reason":"subscription yet available","message":"{ Message:\"subscription yet available\", SubscriptionUID:\"46b62920-c519-4555-8973-3b28a7a29463\" }"}
我得到这个 JsonMappingException ：
Cannot construct instance of `com.ids.utilities.DeserializeSubscription` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
at [Source: (String)"{"code":null,"reason":"subscription yet available","message":"{ Message:\"subscription yet available\", SubscriptionUID:\"46b62920-c519-4555-8973-3b28a7a29463\" }"}"; line: 1, column: 2]
我创建了两个类。第一类：
I've created two classes. The first class:
import lombok.Data;
@Data
public class DeserializeSubscription {
private String code;
private String reason;
private MessageSubscription message;
public DeserializeSubscription(String code, String reason, MessageSubscription message) {
super();
this.code = code;
this.reason = reason;
this.message = message;
}
和第二类
import lombok.Data;
@Data
public class MessageSubscription {
private String message;
private String subscriptionUID;
public MessageSubscription(String message, String subscriptionUID) {
super();
this.message = message;
this.subscriptionUID = subscriptionUID;
}
在主类中：
try
{
ObjectMapper mapper = new ObjectMapper();
mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
DeserializeSubscription desSub=null;
desSub=mapper.readValue(e.getResponseBody(), DeserializeSubscription.class);
System.out.println(desSub.getMessage().getSubscriptionUID());
}
catch (JsonParseException e1) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (JsonMappingException e1) {
System.out.println(e1.getMessage());
e.printStackTrace();
}
catch (IOException e1) {
// TODO Auto-generated catch block
e.printStackTrace();
}
我找到了此解决方案，但没有使用
I've found this solution but I didn't work ithttps://facingissuesonit.com/2019/07/17/com-fasterxml-jackson-databind-exc-invaliddefinitionexception-cannot-construct-instance-of-xyz-no-creators-like-default-construct-exist-cannot-deserialize-from-object-value-no-delega/
我在应用程序中使用的杰克逊专家
The jackson maven I'm using in my application
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.10.2</version>
</dependency>
推荐答案
您必须考虑以下几种情况：
You have to consider few cases:
-
message字段在JSON中是原始的字符串。在POJO级别上，它是MessageSubscription对象。 - <$ c $
JSON中的c> message 值包含不带引号的属性名称，这是非法的，但Jackson会处理它们 - 如果构造函数不适合
JSON，我们需要使用注释对其进行配置。
messagefield inJSONis primitiveString. OnPOJOlevel it is anMessageSubscriptionobject.messagevalue inJSONcontains unquoted property names which is illegal butJacksonhandles them as well.- If constructor does not fit to
JSONwe need to configure it using annotations.
要处理未加引号的名称，我们需要启用功能。要处理 JSON 有效负载和 POJO 之间的不匹配，我们需要为 MessageSubscription实现自定义反序列化器类。
To handle unquoted names we need to enable ALLOW_UNQUOTED_FIELD_NAMES feature. To handle mismatch between JSON payload and POJO we need to implement custom deserialiser for MessageSubscription class.
自定义反序列化器可能如下所示：
Custom deserialiser could look like this:
class MessageSubscriptionJsonDeserializer extends JsonDeserializer<MessageSubscription> {
@Override
public MessageSubscription deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
final String value = p.getValueAsString();
final Map<String, String> map = deserializeAsMap(value, (ObjectMapper) p.getCodec(), ctxt);
return new MessageSubscription(map.get("Message"), map.get("SubscriptionUID"));
}
private Map<String, String> deserializeAsMap(String value, ObjectMapper mapper, DeserializationContext ctxt) throws IOException {
final MapType mapType = ctxt.getTypeFactory().constructMapType(Map.class, String.class, String.class);
return mapper.readValue(value, mapType);
}
}
现在，我们需要自定义 DeserializeSubscription 的构造函数：
Now, we need to customise DeserializeSubscription's constructor:
@Data
class DeserializeSubscription {
private String code;
private String reason;
private MessageSubscription message;
@JsonCreator
public DeserializeSubscription(
@JsonProperty("code") String code,
@JsonProperty("reason") String reason,
@JsonProperty("message") @JsonDeserialize(using = MessageSubscriptionJsonDeserializer.class) MessageSubscription message) {
super();
this.code = code;
this.reason = reason;
this.message = message;
}
}
示例用法：
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.type.MapType;
import lombok.Data;
import java.io.File;
import java.io.IOException;
import java.util.Map;
public class JsonPathApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
ObjectMapper mapper = new ObjectMapper();
mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
mapper.enable(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES);
DeserializeSubscription value = mapper.readValue(jsonFile, DeserializeSubscription.class);
System.out.println(value);
}
}
对于提供的 JSON 有效负载会打印：
For provided JSON payload above example prints:
DeserializeSubscription(code=null, reason=subscription yet available, message=MessageSubscription(message=subscription yet available, subscriptionUID=46b62920-c519-4555-8973-3b28a7a29463))
这篇关于无法使用杰克逊从对象值反序列化（无基于委托或基于属性的创建者）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！