Java Generics : Object Mapper Converting JSON to Java Object

Question

I would like to deserialize a json string to a java object. I wanted to write a generic method.

public class ObjectSerializer<T> {

    T t;
    private ObjectMapper mapper = new ObjectMapper();


  /*  public Person deSerial(String json) throws Exception {
        TypeReference<Person> typeRef = new TypeReference<Person>() {};

        return mapper.readValue(json, typeRef);
    } */

    public T deSerialize(String jsonInput) throws Exception {
        TypeReference<T> typeRef
                = new TypeReference<T>() {};

       return mapper.readValue(jsonInput, typeRef);
    }
}

When I call deSerialize(validPersonJsonString) [validPersonJsonString : valid person JSON String], it is not working, it it throwing me the error:

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.example.Person.

Whereas, when in call the commented deSerial method, it works fine. Please explain the issue.

Thanks.

I don't see the point for using a generic here. Just pass the desired class to deSerialize, so calling it like deSerialize(json, Person.class);. Much easier, less boilerplate. — Tom
– Tom, Commented Feb 15, 2019 at 9:47
HI @Tom, Tomorrow I want to use with Employee.class how would I use it? I don't want to write another method for Employee.class — Raghu
– Raghu, Commented Feb 15, 2019 at 9:47
@Raghu use Class<T>? exactly the same way ObjectMapper already does to allow you to make JSONs into objects. — Worthless
– Worthless, Commented Feb 15, 2019 at 9:49
@SHAHAKASH Your comment is wrong. You're mixing a method definition and the method call. — Tom
– Tom, Commented Feb 15, 2019 at 9:55

Darshan Mehta · Accepted Answer · 2019-02-15 09:55:23Z

4

Jackson doesn't support TypeReference with generic type parameters because of type erasure. Here's the bug about it.

As far as your use case is concerned, you don't need to use ObjectSerializer class at all. You can directly expose ObjectMapper object to your service layer and perform the deserialization.

If you want to shield the json serializing mechanism from your service layer then you can wrap ObjectMapper implementation into another class (like you have done in your code) but then, accept the class type as a method argument rather than a generic type.

answered Feb 15, 2019 at 9:55

Darshan Mehta

31k14 gold badges75 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Raghu Over a year ago

Person person = mapper.readValue(inputJson,Person.class); Thanks. Accepted the answer.

Collectives™ on Stack Overflow

Java Generics : Object Mapper Converting JSON to Java Object

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related