Got UnrecognizedPropertyException when the field name has a capital letter in second position

[maximevw]

Hello,

I'm using Jackson (version 2.18.2, through quarkus-jackson 3.17.8 + additional dependencies to jackson-dataformat-yaml and jackson-datatype-jsr310) to parse a YAML file like this one:

fields:
  - name: myField
    section:
        xStart: 10
        yStart: 20

I have the following Java objects (I use Lombok annotations):

@Data
public class PageDescriptor {
  private List<FieldDescriptor> fields;
}

@Data
public class FieldDescriptor {
  private String name;
  private Section section;
}

@Data
public class Section {
  private int xStart;
  private int yStart;
}

When I try to deserialize the YAML file into a Java object of type PageDescriptor using the code below:

ObjectMapper ymlMapper = new ObjectMapper(new YAMLFactory());
ymlMapper.findAndRegisterModules();
PageDescriptor pageDescriptor = ymlMapper.readValue(getClass().getClassLoader().getResource("test.yaml"), PageDescriptor.class);

I got this error:

Caused by: com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "xStart" (class com.test.Section), not marked as ignorable (4 known properties: "xstart", "ystart"])
 at [Source: (URL); line: 45, column: 22] (through reference chain: com.test.PageDescriptor["fields"]->java.util.ArrayList[0]->com.test.FieldDescriptor["section"]->com.test.Section["xStart"])
        at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:61)
        at com.fasterxml.jackson.databind.DeserializationContext.handleUnknownProperty(DeserializationContext.java:1153)
        at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:2241)
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1821)
        at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1799)
        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.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:310)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer._deserializeFromArray(CollectionDeserializer.java:361)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:246)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:30)
        at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:310)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer._deserializeFromArray(CollectionDeserializer.java:361)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:246)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:30)
        at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:310)
        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:4917)
        at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3791)
        at com.test.GenerationService.generate(GenerationService.java:80)
        at com.test.GenerationService_ClientProxy.generate(Unknown Source)
        at com.test.GenerationService_Observer_Synthetic_jMJAdbQB0LYH0ZTEbOid3CLUQ6Y.notify(Unknown Source)
        at io.quarkus.arc.impl.EventImpl$Notifier.notifyObservers(EventImpl.java:351)
        ... 17 more

If I modify the yaml file to replace xStart and yStart by xstart and ystart respectively, the parsing works correctly.
If I rename the field xStart into xxStart, for example, into my class Section, I'm able to parse correctly the field xxStart in the yaml file.

I don't know if the root cause of the bug is in this project or in jackson-databind one.

[cowtowncoder]

This is a known problem with field names like xStart, Lombok & Jackson. You need to use @JsonProperty to indicate proper casing here unfortunately.
Issue is not specific to YAML module.

The problem is that accessor (getter) generated has name that does not translate to xStart -- it is due to Lombok basing things on field name (creating accessor names), and Jackson starting from accessor. And for this one particular case (well, leading upper-case would have similar issue) expected names do not match, and cannot be determined as things are.

In future it might be possible to address this in jackson-databind either by allowing case-insensitive matching of possible names b/w Fields and Getters/Setters, or by allowing detection to start with Fields as starting point.
But this is not going to be short-term thing to do, which is why I suggest use of @JsonProperty for specific properties.