如何使用jackson（Java）反序列化对象中的json对象？

Question

如何使用 jackson(Java) 在 Object 中反序列化 json 对象（在我的情况下，Offer 对象存在于 current 字段中）？

输入字符串：

message.getMessage();

{"header":"OFFER","message":"{\"author\":\"Peter Smith\",\"previous\":null,\"current\":{\"id\ ":\"eOUQieQdvB\",\"authorUserId\":\"foo\"}}"}

ObjectMapper mapper = new ObjectMapper();
PushEventMessage<PushEvent<Offer>> pushEventMessage = mapper.readValue(message.getMessage(), PushEventMessage.class);
pushEventMessage.getMessage();

{"author":"Peter Smith","previous":null,"current":{"id":"eOUQieQdvB","authorUserId":"foo"}}

PushEvent<Offer> pushEvent = mapper.readValue(pushEventMessage.getMessage(), PushEvent.class);
pushEvent.getAuthor(); // is OK and contain "Peter Smith"

pushEvent.getCurrent() // is KO and contain {id=eOUQieQdvB, authorUserId=foo}

我要反序列化：

Offer offer= mapper.readValue(pushEvent.getCurrent() + "", Offer.class);

我的错误是：

com.fasterxml.jackson.core.JsonParseException: Unexpected character ('i' (code 105)): was expecting double-quote to start field name
 at [Source: (String)"{id=eOUQieQdvB, authorUserId=foo,

EDIT 1，我添加PushEvent<T> 类。

import lombok.*;

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class PushEvent<T> {
    String author;
    T previous;
    T current;
    String error;
}

EDIT 2，我试试这个，但结果是一样的

PushEvent<Offer> pushEvent = mapper.readValue(pushEventMessage.getMessage().replaceAll("\\\"", "\""), PushEvent.class);

我采用@Smutje 的解决方案，这解决了第一个问题。！！

编辑 3，我在 Offer 对象中有一个 java.time.ZonedDateTime。

{"author":"Peter Smith","previous":null,"current":{"id":"00Yno9WwsL","authorUserId":"foo","createdAt":{"offset":{ "totalSeconds":0,"id":"Z","rules":{"transitionRules":[],"transitions":[],"fixedOffset":true}},"zone":{"id": "UTC","rules":{"transitionRules":[],"transitions":[],"fixedOffset":true}},"dayOfMonth":11,"dayOfWeek":"SUNDAY","dayOfYear":42 ,"月":"二月","年":2018,"小时":1,"分钟":0,"纳米":0,"秒":0,"月值":2,"年表":{ "id":"ISO","calendarType":"iso8601"}}}}

我有这个错误：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `java.time.ZonedDateTime` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (String)"{"id":"00Yno9WwsL","authorUserId":"foo", ....."createdAt":{"offset":{"totalSeconds":0,...

EDIT 4，我添加Offer 类。

@Slf4j
@Data
@NoArgsConstructor
public class Offer {

    @Id
    protected String id;

    protected String authorUserId;

    protected ZonedDateTime createdAt;

}

Answer 1

由于许多映射框架无法使用泛型或继承层次结构正确反序列化对象，因此以下是丑陋的，但应该是可能的

PushEvent<Offer> pushEvent = mapper.readValue(pushEventMessage.getMessage(), PushEvent.class);
String serializedOffer = mapper.writeValueAsString(pushEventMessage.getCurrent());
Offer offer = mapper.readValue(serializedOffer, Offer.class);
pushEvent.setCurrent(offer);

说明：Jackson 将您的内部对象反序列化不是您所说的 Offer，而是作为 LinkedHashMap 在将 JSON 对象读取为实际 Offer 之前再次序列化为 JSON 对象。

您尝试将LinkedHashMap 读入Offer 失败，因为您（隐含地）使用LinkedHashMap 的toString 表示来解析不 生成有效JSON 的哪个。 p>

编辑 4 答案：，如果 Object 包含 ZonedDateTime。读写时使用：

ObjectMapper mapper = new ObjectMapper().registerModule(new JavaTimeModule());
mapper.setDateFormat(new StdDateFormat());

Answer 2

错误消息告诉您问题出在哪里：“期望用双引号来开始字段名称”。

通过简单检查，您读取 json 字符串的代码看起来是正确的，因此请确保您提供的数据有效。

提示：您可以通过简单地序列化演示对象来生成已知良好的数据：

new ObjectMapper().writeValueAsString(demoObject);

然后您可以尝试使用该字符串运行您的代码，这将告诉您您的输入是否有效。