DeserializationProblemHandler.handleUnexpectedToken() cast Object to String

[yacine-pc]

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Describe the bug

I am currently migrating from Jackson version 2.10.0 to 2.15.1 and I seem to be encountering a bug. When attempting to deserialize JSON into a POJO, a JsonMappingException (Cf. Stacktrace below) is thrown for the age field in the simplified code snippet provided below. The same code works perfectly with version 2.10.0.

Version Information

2.15.2

Reproduction

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.DeserializationProblemHandler;

import java.io.IOException;

class Person {
    public String id;
    public String name;
    public Long age;
}

class MongoTypeProblemHandler extends DeserializationProblemHandler {
    protected static final String NUMBER_LONG_KEY = "$numberLong";

    @Override
    public Object handleUnexpectedToken(DeserializationContext ctxt, JavaType targetType, JsonToken t, JsonParser p, String failureMsg) throws IOException {
        if (targetType.getRawClass().equals(Long.class) && JsonToken.START_OBJECT.equals(t)) {
            JsonNode tree = p.readValueAsTree();
            if (tree.get(NUMBER_LONG_KEY) != null) {
                try {
                    return Long.parseLong(tree.get(NUMBER_LONG_KEY).asText());
                } catch (NumberFormatException e) {
                }
            }
        }
        return NOT_HANDLED;
    }
}

public class Main {
    public static void main(String[] args) {
        String json = "{\"id\":  \"12ab\", \"name\": \"Bob\", \"age\": {\"$numberLong\": \"10\"}}";

        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.addHandler(new MongoTypeProblemHandler());
        try {
            Person person = objectMapper.readValue(json, Person.class);
            System.out.println("id:" + person.id);
            System.out.println("name:" + person.name);
            System.out.println("age:" + person.age);
        } catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }

    }
}

Expected behavior

It should deserialize the JSON to POJO like version 2.10.0 for example

Additional context

Exception in thread "main" java.lang.RuntimeException: com.fasterxml.jackson.databind.JsonMappingException: class java.lang.Long cannot be cast to class java.lang.String (java.lang.Long and java.lang.String are in module java.base of loader 'bootstrap') (through reference chain: org.example.Person["age"])
at org.example.Main.main(Main.java:50)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: class java.lang.Long cannot be cast to class java.lang.String (java.lang.Long and java.lang.String are in module java.base of loader 'bootstrap') (through reference chain: org.example.Person["age"])
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:402)
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:361)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.wrapAndThrow(BeanDeserializerBase.java:1853)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:316)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:323)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4825)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3772)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3740)
at org.example.Main.main(Main.java:45)
Caused by: java.lang.ClassCastException: class java.lang.Long cannot be cast to class java.lang.String (java.lang.Long and java.lang.String are in module java.base of loader 'bootstrap')
at com.fasterxml.jackson.databind.DeserializationContext.extractScalarFromObject(DeserializationContext.java:943)
at com.fasterxml.jackson.databind.deser.std.StdDeserializer._parseLong(StdDeserializer.java:949)
at com.fasterxml.jackson.databind.deser.std.NumberDeserializers$LongDeserializer.deserialize(NumberDeserializers.java:575)
at com.fasterxml.jackson.databind.deser.std.NumberDeserializers$LongDeserializer.deserialize(NumberDeserializers.java:550)
at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:314)
... 6 more

[cowtowncoder]

First things first: it would be good to verify that the issue still occurs in 2.17.2 as 2.15 is not the latest release.
I suspect it does but it'd be good to confirm.

Failure itself does seem like a regression.

[yacine-pc]

Yes sorry for that, just tested with version 2.17.2, and the same error occurs. Here is the stack trace for 2.17.2:

Exception in thread "main" java.lang.RuntimeException: com.fasterxml.jackson.databind.JsonMappingException: class java.lang.Long cannot be cast to class java.lang.String (java.lang.Long and java.lang.String are in module java.base of loader 'bootstrap') (through reference chain: org.example.Person["age"])
	at org.example.Main.main(Main.java:50)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: class java.lang.Long cannot be cast to class java.lang.String (java.lang.Long and java.lang.String are in module java.base of loader 'bootstrap') (through reference chain: org.example.Person["age"])
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:402)
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:361)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.wrapAndThrow(BeanDeserializerBase.java:1937)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:312)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
	at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:342)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4905)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3848)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3816)
	at org.example.Main.main(Main.java:45)
Caused by: java.lang.ClassCastException: class java.lang.Long cannot be cast to class java.lang.String (java.lang.Long and java.lang.String are in module java.base of loader 'bootstrap')
	at com.fasterxml.jackson.databind.DeserializationContext.extractScalarFromObject(DeserializationContext.java:958)
	at com.fasterxml.jackson.databind.deser.std.StdDeserializer._parseLong(StdDeserializer.java:954)
	at com.fasterxml.jackson.databind.deser.std.NumberDeserializers$LongDeserializer.deserialize(NumberDeserializers.java:575)
	at com.fasterxml.jackson.databind.deser.std.NumberDeserializers$LongDeserializer.deserialize(NumberDeserializers.java:550)
	at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:310)
	... 6 more

[cowtowncoder]

Thank you @yacine-pc .

I am not sure if this can be fixed or not (and won't necessarily have time to dig in deep in near future).

In the meantime I would recommend writing a custom deserializer, attach it like so:

@JsonDeserialize(using = MyLongDeserializer.class)
public Long age;

to handle things as expected. This would be more reliable mechanism than relying on DeserializationProblemHandler for recovery.

[cowtowncoder]

Had some time to look into this and it's... complicated. I can see what is happening: it has to do 2.12-added mechanism to help work with XML content. Cast exception is side-effect, but I am not quite sure yet how to resolve this issue.

[cowtowncoder]

Ok. I know how to fix this... but fix cannot, alas, go in 2.19 since it requires some changes to semantics of extension point which, while meant as internal is still opened up and used across modules.

[cowtowncoder]

Phew. Lots of mechanical changes as this affects Joda and Java 8 Time modules as well.

Now fixed for 2.20(.0) (and 3.0.0(-rc5)).