Property-based Creator clobbers enclosing value's `JsonParser.currentValue()`

[deskoh]

Jackson 3 Deserialization issues with Spring Boot Plugin

Repo to reproduce the issue: deskoh/jackson-issue

To reproduce the issue, run the tests

./gradlew test

Jackson 3 using custom deserializer of a JSON with nested object will throw an exception.

tools.jackson.databind.DatabindException: class com.deskoh.entities.SourceSystem cannot be cast to class com.deskoh.entities.Project (com.deskoh.entities.SourceSystem and com.deskoh.entities.Project are in unnamed module of loader 'app')
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); byte offset: FasterXML/jackson-core#119] (through reference chain: com.deskoh.entities.Project["assets"])
	at app//tools.jackson.databind.DatabindException.wrapWithPath(DatabindException.java:111)
	at app//tools.jackson.databind.deser.bean.BeanDeserializerBase.wrapAndThrow(BeanDeserializerBase.java:1936)
	at app//tools.jackson.databind.deser.bean.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:654)
	at app//tools.jackson.databind.deser.bean.BeanDeserializer.deserialize(BeanDeserializer.java:200)
	at app//tools.jackson.databind.deser.DeserializationContextExt.readRootValue(DeserializationContextExt.java:266)
	at app//tools.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2639)
	at app//tools.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1622)
	at app//com.deskoh.entities.ProjectTest.given_project_can_deserialize(ProjectTest.java:24)
Caused by: java.lang.ClassCastException: class com.deskoh.entities.SourceSystem cannot be cast to class com.deskoh.entities.Project (com.deskoh.entities.SourceSystem and com.deskoh.entities.Project are in unnamed module of loader 'app')
	at com.deskoh.entities.AssetDeserializer.deserialize(AssetDeserializer.java:19)
	at com.deskoh.entities.AssetDeserializer.deserialize(AssetDeserializer.java:13)
	at tools.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:120)
	at tools.jackson.databind.deser.bean.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:652)
	... 5 more

Cause

The exception is thrown during custom deserialization.

// src\main\java\com\deskoh\entities\AssetDeserializer.java
// `p.currentValue()` will evaluate to `SourceSystem` instead of `Project`
Project project = (Project) p.currentValue();

However, the deserialization will work (and unit test pass) if either

1. -parameters flag is removed during compilation, OR

   Note: Adding org.springframework.boot gradle plugin will enable the -parameters flag --as well.

   tasks.withType(JavaCompile).configureEach {
   -    options.compilerArgs << "-parameters"
   }

2. AllArgsConstructor of SourceSystem is removed, OR

   Note: Similar behaviour with lombok @AllArgsConstructor annotation

   public class SourceSystem {
   -   public SourceSystem(String id, String name) {
   -       this.id = id;
   -       this.name = name;
   -   }
   }

3. Jackson 2 is used (see jackson2 branch)

[cowtowncoder]

Wrong repo, transfer.

[cowtowncoder]

Would need a stand-alone reproduction (no Spring Boot or Lombok dependency), ideally unit test.
And if possible, inline here instead of separate project (although stand-alone GH repo acceptable).

Issue cannot be trouble-shot based on description only.

[deskoh]

Not sure if you have seen the repo linked above. The unit test is a vanilla junit test without any spring boot annotation. Also lombok is excluded from the project dependencies.

I have further narrowed down the issue to the -parameters flag during compilation (and updated the repo):

tasks.withType(JavaCompile).configureEach {
-    options.compilerArgs << "-parameters"
}

The tests can pass with the same flag using Jackson 2 (can verify using the jackson2 branch).

[yihtserns]

Summary:

public class AssetDeserializer extends ValueDeserializer<List<Asset>> {
    ...
    @Override
    public List<Asset> deserialize(JsonParser p, DeserializationContext ctxt) throws JacksonException {
        ...
        Project project = (Project) p.currentValue();
        ...
    }
}

...
public class Project {                                // Assumes this will be the JsonParser.currentValue()...
    private SourceSystem source;                      // ...but .currentValue() was this instead...
    @JsonDeserialize(using = AssetDeserializer.class) // ...when running this...
    private List<Asset> assets;
}

Can implementations assume JsonParser.currentValue() is definitely the parent instance of a field being deserialized?

[deskoh]

You are right. The assumptions could be wrong. Just wondering any documentation could explain how the change in compiler flag could affect the behavior and why Jackson 2 is not affected.

[cowtowncoder]

One more thing to include would be definition of Asset.

But I can speculate a bit here: currentValue() is updated when parsing, normally, but when content is buffered (in TokenBuffer), situation is different. Buffering often happens due to use of Constructor (either with explicit @JsonCreator or auto-detection).
My guess is that with Jackson 3, auto-detection of POJO constructor happens when parameter names are included --in Jackson 2 one must register jackson-module-parameter-names which is in-built in Jackson 3.

More specifically, current value cannot be Project instance until it is constructed -- which cannot happen before Asset is deserialized if (but only if!) Asset is passed via constructor, no matter what.

So to fix the issue it may be necessary to prevent use of parameters-taking constructor. I think adding

@JsonCreator(mode = JsonCreator.Mode.DISABLED)

(or making constructor non-public if possible).

I hope this helps.

[deskoh]

For Jackson 2, adding jackson-module-parameter-names modules also does not change the behavior. I guess some internals has changed for Jackson 3. I'm ok to close the issue.

[cowtowncoder]

Will try this with Claude; ideally should behave similarly.

[cowtowncoder]

And that works, pr coming.