如何使用Jackson（Java）在Object中反序列化JSON Object？

Question

How to deserialize json Object ( Offer object present in current field in my case) in Object with jackson(Java)?

input String:

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}

I want deserialize:

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

My error is:

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 , I add PushEvent<T> class.

import lombok.*;

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

EDIT 2 , I try this but the result is the same

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

I take the solution of @Smutje and this fix the 1st problem. !!

EDIT 3 , I have a java.time.ZonedDateTime in Offer object.

{"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,"month":"FEBRUARY","year":2018,"hour":1,"minute":0,"nano":0,"second":0,"monthValue":2,"chronology":{"id":"ISO","calendarType":"iso8601"}}}}

I have this error:

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 , I add Offer class.

@Slf4j
@Data
@NoArgsConstructor
public class Offer {

    @Id
    protected String id;

    protected String authorUserId;

    protected ZonedDateTime createdAt;

}

Answer 1

Due to the inability of many mapping frameworks to properly deserialize objects using generics or inheritance hierarchies the following is ugly but should be possible

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);

Explanation: Jackson deserializes your inner object not as Offer as you stated it but rather as a LinkedHashMap which is being serialized as a JSON object again before reading the JSON object as actual Offer .

Your attempt to read the LinkedHashMap into a Offer failed because you (implicitely) used the toString representation of LinkedHashMap to parse which does not produce valid JSON.

EDIT 4 answer: , if Object contain a ZonedDateTime . Use this when write and read:

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

Answer 2

The error message tells you what the problem is: "was expecting double-quote to start field name".

From a brief inspection, your code to read the json string looks correct, so make sure you are providing it with valid data.

Hint: you can generate known good data by simply serialising a demo object with:

new ObjectMapper().writeValueAsString(demoObject);

You can then try to run your code with that string, and this will tell you if your input is valid or not.