ERROR: Can not deserialize instance of java.lang.String out of START_OBJECT token

Question

I'm using Jackson version 2.7.4 + EJB 3.0 with WebSphere 9.0. The classe has an attribute String date as below:

Class:

@Data
@EqualsAndHashCode(callSuper = false)
@NoArgsConstructor
@AllArgsConstructor
public class filter {

    private String date;
    ...
}

When I call the method shows the error below.

Error:

Caused by: org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token at [Source: org.apache.cxf.transport.http.AbstractHTTPDestination$1@b3f4efe6; line: 1, column: 163] at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:160) at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:194) at org.codehaus.jackson.map.deser.StdDeserializer$StringDeserializer.deserialize(StdDeserializer.java:607) at org.codehaus.jackson.map.deser.StdDeserializer$StringDeserializer.deserialize(StdDeserializer.java:576) at org.codehaus.jackson.map.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:149) at org.codehaus.jackson.map.deser.SettableBeanProperty$MethodProperty.deserializeAndSet(SettableBeanProperty.java:237) at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:496) at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:350) at org.codehaus.jackson.map.ObjectMapper._readValue(ObjectMapper.java:1961) at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:889) at org.codehaus.jackson.jaxrs.JacksonJsonProvider.readFrom(JacksonJsonProvider.java:410) at org.apache.cxf.jaxrs.utils.JAXRSUtils$2.run(JAXRSUtils.java:1408) at java.security.AccessController.doPrivileged(AccessController.java:738) at org.apache.cxf.jaxrs.utils.JAXRSUtils.readFromMessageBodyReader(JAXRSUtils.java:1404) at org.apache.cxf.jaxrs.utils.JAXRSUtils.readFromMessageBody(JAXRSUtils.java:1354) at org.apache.cxf.jaxrs.utils.JAXRSUtils.processParameter(JAXRSUtils.java:878) at org.apache.cxf.jaxrs.utils.JAXRSUtils.processParameters(JAXRSUtils.java:837) at org.apache.cxf.jaxrs.interceptor.JAXRSInInterceptor.processRequest(JAXRSInInterceptor.java:265) at org.apache.cxf.jaxrs.interceptor.JAXRSInInterceptor.handleMessage(JAXRSInInterceptor.java:95) ... 29 more

Maven dependencies:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.7.4</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.7.4</version>
</dependency>

Does anyone have any idea?

I call in a resource class. It's a PUT. The data come the front end angular. — Luciana Oliveira
– Luciana Oliveira, Commented Aug 9, 2022 at 0:52

Omar Hussien · Accepted Answer · 2022-08-09 07:36:47Z

1

The start of the object should be like this { ,Make sure the json from the Front doesn't start with [

{
  "data": "any value"
}

answered Aug 9, 2022 at 7:36

Omar Hussien

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7 Comments

Luciana Oliveira Over a year ago

Thanks to answer. I checked and the object started with { ... }. I think the problem is in the backend. Do you have any idea?

Luciana Oliveira Over a year ago

The object DateTime in the frontend:

export interface dateTime {   year: number;   monthValue: number;   month: string;   dayOfMonth: number;   dayOfYear: number;   dayOfWeek: string;   hour: number;   minute: number;   second: number;   nano: number;   chronology: Chronology; }

David Conrad Over a year ago

@LucianaOliveira There is no date: string; Are you expecting Jackson to convert all those separate date-related fields into a date, and then convert the date to a string, and then store it into the date field? That's not how it works. The model on both the frontend and the backend need to match.

David Conrad Over a year ago

@LucianaOliveira It doesn't matter if the application is new or old. That isn't how Jackson works. You have to make the data models match. If you cannot change the frontend or the backend then it will simply never work.

David Conrad Over a year ago

@LucianaOliveira Do the answers to this question help you? For the one that suggests taking the first 10 characters, I think you could use the entire ISO string if it was a ZonedDateTime on the backend.

|

Luciana Oliveira · Accepted Answer · 2022-08-10 13:01:41Z

It's a beginner question, so if you have the same error with different types the solution is the same.

JsonMappingException: Can Not Deserialize Instance Of

The Problem : This exception is thrown if the wrong type is used while deserializing.

The Solution: Checking the attribute has the different types.

In my problem, the solution was to change the type of angular date to a angular's native date to match to backend java type. You can create a main class to test your backend code like below.

Thanks the developers that comment this post. I could see the rubber duck technique applyed here. Thanks a lot.

public static void main(String[] args) {
    
    ObjectMapper objectMapper = new ObjectMapper();
    String json = ""; //Use your string json
    
    try {
        Person personDeserialized = objectMapper.readValue(json, Person.class);
    
    } catch (JsonParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (JsonMappingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

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