Flatten nested JSON object using jackson

Question

This question's answer (Convert JSON many objects to single JSON using Jackson) explains how to flatten JSON using Jackson

But my json is like this

{
  "field1":"value1",
  "field2":"value2",
  "field3": {
     "type":{
        "f1":"v1",
        "f2":"v2"
     }
  }
}

I need something like this

{
  "field1":"value1",
  "field2":"value2",
  "field3": {
        "f1":"v1",
        "f2":"v2"
  }
}

so that field3.type is put directly into field3 and then deserialize to Json object

I need steps to do this just using jackson annotations and not by unpacking the nested object.

score 0 · Answer 1 · answered Mar 14 '23 at 17:48

Use the @JsonCreator annotation for the constructor of field3:

public class Flattened implements Serializable {

    static ObjectMapper objectMapper = new ObjectMapper();
    
    public String field1;
    public String field2;
    public Field3Class field3;
    
    public static void main(String[] args) throws IOException {

        String jsonSerialised = "{\r\n" + 
                "  \"field1\":\"value1\",\r\n" + 
                "  \"field2\":\"value2\",\r\n" + 
                "  \"field3\": {\r\n" + 
                "     \"type\":{\r\n" + 
                "        \"f1\":\"v1\",\r\n" + 
                "        \"f2\":\"v2\"\r\n" + 
                "     }\r\n" + 
                "  }\r\n" + 
                "}  ";
        
        Flattened flattenedValue = objectMapper.readValue(jsonSerialised, Flattened.class);
        objectMapper.writeValue(System.out, flattenedValue);
    }
    
    public static class Field3Class implements Serializable {
        public String f1;
        public String f2;
        @JsonCreator
        public Field3Class(@JsonProperty("type") Type type) {
            this.f1 = type.f1;
            this.f2 = type.f2;
        }
        
        public static class Type implements Serializable {
            public String f1;
            public String f2;
       }
    }
}

Output:

{"field1":"value1","field2":"value2","field3":{"f1":"v1","f2":"v2"}}

Flatten nested JSON object using jackson

1 Answers1