Get value from object by key in java

I am getting object in the response of entityManager.find method. and i want to get values from that object by passing key. but i din't get any success. For example :- my entity :-

@entity
class Test (){
public Long id;
public String name ;
public String descr;
}

and i am getting object in the response of below code.

`Object obj=`entitymanager.find(classname,id);

Note :- Instead of object i can't use entity's object directly because input class name can be dynamically pass that's why i am taking response in Object.

Now i want to get value from object by passing key something like that obj.getvalue("id");

I tried below things to make it done :-

1. Map<String, Object> user = (Map<String, Object>)obj;

2. Used json simple parser to pare it.

   JSONParser parser = new JSONParser();

   JSONObject jsonObject =parser.parse(obj.toString());

But din't get any success.

Please help me out.