Vfrdtyky

When we deserialize JSON into POJO, JACKSON throws a Mismatch Input exception in case of data type mismatch, which is expected.
So my question is, "Is there any feature flag available in Jackson or Gson, to set the default value for mismatched field during deserialization?"

I understand that we can implement the custom deserializer for such fields, where random input value can be expected.
But is this already supported using some flag in any serialization deserialization java library?

Sample Code:

import com.fasterxml.jackson.databind.ObjectMapper;



import lombok.Data;



import java.io.IOException;



public class JsonSample {

@Data

static class Address {

    String houseAddress;

}



@Data

static class InnerJsonClass {

    Integer integerField;

    Address address;

}



public static void main(String args) {

    String jsonInput = "{"integerField": 1,"address":"hello"}";

    try {

        ObjectMapper objectMapper = new ObjectMapper();

        InnerJsonClass object = objectMapper.readValue(jsonInput, InnerJsonClass.class);

        System.out.println(object.toString());

    } catch (IOException e) {

        e.printStackTrace();

    }

}}

Exception:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of com.paytm.logistics.JsonSample$Address (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('hello')
at [Source: (String)"{"integerField": 1,"address":"hello"}"; line: 1, column: 30] (through reference chain: com.paytm.logistics.JsonSample$InnerJsonClass["address"])
at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1342)
at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1031)
at com.fasterxml.jackson.databind.deser.ValueInstantiator._createFromStringFallbacks(ValueInstantiator.java:371)
at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:323)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1366)
at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:171)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:161)
at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:127)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:288)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2992)
at com.paytm.logistics.JsonSample.main(JsonSample.java:25)

Address is a object, not a String.

String jsonInput = "{"integerField": 1,"address":{"houseAddress": "hello"}}";

Try this

Your jsoninput is not in correct format it should be like below:
objectMapper will only convert value in specified object when json and pojo declaration mapping are same.

 String jsonInput = "{"integerField": 1,"address":{"houseAddress": "hello"}}";

or if you don't want to change string json then you have to use code like below

 @Data

    static class InnerJsonClass {

        Integer integerField;

        String address;

    }