Jackson deserialize extra fields as Map

Jackson deserialize extra fields as Map

If you want to deserialize JSON data into a Java object using Jackson while preserving extra, unrecognized fields as a Map, you can use Jackson's @JsonAnySetter annotation. This annotation allows you to capture all unrecognized properties during deserialization and store them in a Map field within your Java object.

Here's an example of how to achieve this:

  • Import the necessary Jackson annotations and classes:
import com.fasterxml.jackson.annotation.JsonAnySetter; import com.fasterxml.jackson.databind.ObjectMapper; import java.util.HashMap; import java.util.Map;
  • Define a Java class for your JSON data with a Map field to hold extra properties:
public class MyData { private String name; private int age; private Map<String, Object> extraFields = new HashMap<>(); // Getters and setters for name, age, and extraFields @JsonAnySetter public void setExtraFields(String key, Object value) { extraFields.put(key, value); } }

In this example:

  • name and age are regular fields that match the expected properties in the JSON data.
  • extraFields is a Map field where we'll store unrecognized properties.
  • Deserialize JSON data into the MyData object:
public class Main { public static void main(String[] args) throws Exception { String json = "{\"name\":\"Alice\",\"age\":30,\"city\":\"New York\",\"country\":\"USA\"}"; ObjectMapper objectMapper = new ObjectMapper(); MyData myData = objectMapper.readValue(json, MyData.class); System.out.println("Name: " + myData.getName()); System.out.println("Age: " + myData.getAge()); System.out.println("Extra Fields: " + myData.getExtraFields()); } }

In this code:

  • We deserialize the JSON data into the MyData object using ObjectMapper.
  • Any extra fields that are not explicitly mapped to name or age will be captured in the extraFields map.

When you run this code, it will print:

Name: Alice Age: 30 Extra Fields: {city=New York, country=USA}

As you can see, the extra fields "city" and "country" are stored in the extraFields map. This approach allows you to deserialize JSON data while capturing any additional, unrecognized properties in a flexible Map.

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