如何使用Java中的flexjson来包装JSON？

public JSONSerializer rootName(String rootName)

import flexjson.JSONSerializer;
public class JSONRootNameTest {
   public static void main(String[] args) {
      JSONSerializer serializer = new JSONSerializer().rootName("My_Employee").prettyPrint(true);
      Employee emp = new Employee("Adithya", "Jai", 28, "Hyderabad");
      String jsonStr = serializer.serialize(emp);
      System.out.println(jsonStr);
   }
}
// Employee class<strong>
</strong>class Employee {
   private String firstName;
   private String lastName;
   private int age;
   private String address;
   public Employee() {}
   public Employee(String firstName, String lastName, int age, String address) {
      super();
      this.firstName = firstName;
      this.lastName = lastName;
      this.age = age;
      this.address = address;
   }
   public String getFirstName() {
      return firstName;
   }
   public String getLastName() {
      return lastName;
   }
   public int getAge() {
      return age;
   }
   public String getAddress() {
      return address;
   }
}

{
 "My_Employee": {
 "address": "Hyderabad",
 "age": 28,
 "class": "Employee",
 "firstName": "Adithya",
 "lastName": "Jai"
 }
}