Java Generics not working with Jackson Serlializer

Question

I have a class representing a generic API response:

@Setter
@Getter
public final class ApiResponse<T> {
    private T data;
}

I set the data with the help of Jackson like below:

class Converter<T> {
  ApiResponse<T> create(){
     // some REST calls and form httpResponse before this step
     ApiResponse<T> apiResponse = new ApiResponse();
     T data = objectMapper
         .readValue(httpResponse.body(), new TypeReference<>() {});
     apiResponse.setData(data);
     return apiResponse;
  }
}

Then I tried to use it with a custom object, as shown below:

Converter<MyObject> converter = new Converter<>();
ApiResponse<MyObject> apiResponse = converter.create();

But I observe that apiResponse.getData() always return LinkedHashMap instead of Myobject type.

Here is MyObject class:

@Getter
@Builder
@NoArgsConstructor
@AllArgsConstructor
@JsonIgnoreProperties(ignoreUnknown = true)
public final class MyObject {
  @JsonProperty("childs")
  private ChildObject[] childs;
}

What am I doing wrong here?

here is the http response body for reference:

{
  "childs": [
    {
      "freightLineId": "",
      "shipmentId": "",
      "shipmentVersionId": ""
    }
  ]
}

Answer 1

You can try generic method instead of generic class and pass the class type as parameter inside the method

Converter.java

public class Converter {
    public static ObjectMapper objectMapper = new ObjectMapper();
    public static <T> T create(String json, Class<T> classType) throws Exception {
        return (T) objectMapper.readValue(json, classType);
    }
}

main code

MyObject obj = Converter.create("{\n"
                    + "  \"childs\": [\n"
                    + "    {\n"
                    + "      \"freightLineId\": \"0001\",\n"
                    + "      \"shipmentId\": \"1000\",\n"
                    + "      \"shipmentVersionId\": \"1.0\"\n"
                    + "    }\n"
                    + "  ]\n"
                    + "}", MyObject.class);
            
System.out.println(obj.getChilds());

Code for ApiResponse<T>

public class Converter {
    public static ObjectMapper objectMapper = new ObjectMapper();
    public static <T> ApiResponse<T> create(String json, Class<T> classType) throws Exception {
        ApiResponse<T> res = new ApiResponse<>();
        res.setData((T) objectMapper.readValue(json, classType));
        return res;
    }
}

main code

ApiResponse<MyObject> obj = Converter.create("{\n"
                    + "  \"childs\": [\n"
                    + "    {\n"
                    + "      \"freightLineId\": \"0001\",\n"
                    + "      \"shipmentId\": \"1000\",\n"
                    + "      \"shipmentVersionId\": \"1.0\"\n"
                    + "    }\n"
                    + "  ]\n"
                    + "}", MyObject.class);
System.out.println( obj.getData().getChilds() );