Java泛型：将JSON转换为Java对象的对象映射器

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.

Answer 1

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.