Java 11: guide with Jackson Deserialization for Complex Nested Objects
I'm working with a question when deserializing a complex JSON structure into a Java object using Jackson in my Spring Boot application. The JSON contains nested objects, and some of these objects contain fields that are optional, which can be either null or not present in the JSON string. Here's an example of the JSON I'm trying to deserialize: ```json { "userId": 1, "userName": "JohnDoe", "address": { "street": "123 Main St", "city": "New York" // "state" field is optional and might not be present } } ``` I have the following classes to represent this structure: ```java public class User { private int userId; private String userName; private Address address; // Getters and Setters } public class Address { private String street; private String city; private String state; // This might be null or missing // Getters and Setters } ``` When I attempt to deserialize this JSON using the following code: ```java ObjectMapper objectMapper = new ObjectMapper(); User user = objectMapper.readValue(jsonString, User.class); ``` I receive the following behavior message: ``` com.fasterxml.jackson.databind.JsonMappingException: Unexpected token (VALUE_STRING), expected FIELD_NAME: missing property 'state' (index 1) ``` I've tried adding `@JsonInclude(JsonInclude.Include.NON_NULL)` to the Address class, but that doesn't seem to help. I've also verified that my JSON is valid and well-formed. The scenario seems to stem from the optional nature of the `state` field. I'm using Jackson version 2.12.3 and Spring Boot 2.5.4. Is there a specific configuration I need to set on the ObjectMapper or annotations on the classes to handle this scenario correctly? Any guidance on how to resolve this scenario would be greatly appreciated.