How to Handle "Unrecognized Field" Errors When Deserializing JSON with Jackson?

Jackson with JSON: Resolving "Unrecognized Field" Error

When converting a JSON string to a Java object using Jackson, you may encounter the error "Unrecognized field, not marked as ignorable" if there are unrecognized fields in the JSON. To resolve this issue, Jackson provides two options:

JsonIgnoreProperties Annotation

The @JsonIgnoreProperties annotation allows you to ignore specific fields in the POJO during deserialization. For example, in your case, you can ignore the "wrapper" field:

@JsonIgnoreProperties(ignoreUnknown = true)
class Wrapper { ... }

This will ignore any unrecognized properties, including "wrapper."

Custom Deserializer

If you need more granular control over the ignored properties, you can create a custom deserializer. Override the deserialize method to handle the unrecognized fields:

public class CustomDeserializer extends JsonDeserializer<Wrapper> {
    @Override
    public Wrapper deserialize(JsonParser parser, DeserializationContext context) throws IOException {
        Wrapper wrapper = new Wrapper();
        ObjectCodec codec = parser.getCodec();
        JsonToken token = parser.getCurrentToken();
        while (token != JsonToken.END_ARRAY) {
            if (token == JsonToken.START_OBJECT) {
                Student student = codec.readValue(parser, Student.class);
                wrapper.getStudents().add(student);
            }
            token = parser.nextToken();
        }
        return wrapper;
    }
}

Then, register the custom deserializer with Jackson:

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new SimpleModule().addDeserializer(Wrapper.class, new CustomDeserializer()));

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