How to get response value in java api.

Hi everyone this is my first question related to java. I am new in building api in java i am passing the null value in json i want some random value in json response which are come from database my code is working in java code is below on java.

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.Types;
import com.pal.api.application.ApplicationAPI.DBConnection;
import Modal.AddContactRequest;

public class AddContact {
	public String addContact(AddContactRequest add) {
		Connection c= DBConnection.getConn();		
		//String cc = "";
		String result = "";
		try {
			 CallableStatement stmt= c.prepareCall("{call something( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ? ,?)}");
			 stmt.setString(1, add.getContactType());
			 stmt.setString(2, add.getCategory());
			 stmt.setString(3, add.getSubCategory());
			 stmt.setString(4, add.getTitle());
			 stmt.setString(5, add.getFirstName());
			 stmt.setString(6, add.getMiddleName());
			 stmt.setString(7, add.getLastName());
			 stmt.setString(8, add.getDesignation());
			 stmt.setString(9, add.getMobile());
			 stmt.setString(10, add.getPhoneNo());
			 stmt.setString(11, add.getDOB());
			 stmt.setString(12, add.getDOA());
			 stmt.setString(13, add.getEmail());
             stmt.setInt(14, add.getLocationID());
             stmt.setString(15, add.getActive());
             stmt.setString(16, add.getContactCode());
             stmt.setString(17, "");
             //ResultSet rs = stmt.executeQuery();
             stmt.registerOutParameter(16, Types.VARCHAR);
             stmt.registerOutParameter(17, Types.VARCHAR);
			 int rs = stmt.executeUpdate();		    
		
			 if (rs > 0)
			 {				 
			    String contactcode = stmt.getString(16);
			    contactcode = stmt.getString(16);
			    System.out.println("ContactCode: "+ contactcode);			
			    result = stmt.getString(17);
			    System.out.println("Status: "+ result);
				return result;
			 }
			else
			{
				return result;
			}
		
		}

		catch (Exception e) {
			e.printStackTrace();
		}
		return "{\"msg\":\"Failed to  Create Customer\"}";
	
	}
	

}

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output are come contactcode like this.
Driver loaded
connected
ContactCode: CNT-5959
Status: Insert
 it is working fine.

but i want to make api in java how can i do here is my code
@Path("addcontact")
    @POST
    @Consumes(MediaType.APPLICATION_JSON)
    @Produces(MediaType.APPLICATION_JSON)
    public AddContactResponse addContact(String json)
    {
          System.out.println();
          String msg = "";
          //String contactcode = "CNT-5974";
            AddContactRequest add = null;
            JsonParser jsonParser = new JsonParser();
            JsonElement jsonElement = jsonParser.parse(json);
            if(jsonElement.isJsonObject())
            {
                  JsonObject jsonObject = jsonElement.getAsJsonObject();            
                  add = new AddContactRequest(jsonObject.get("contact_type").getAsString(),jsonObject.get("contact_category").getAsString(), jsonObject.get("contact_sub_category").getAsString(), jsonObject.get("contact_title").getAsString(),
                              jsonObject.get("first_name").getAsString(), jsonObject.get("middle_name").getAsString(), jsonObject.get("last_name").getAsString(), jsonObject.get("Designation").getAsString(),
                              jsonObject.get("mobile").getAsString(), jsonObject.get("phone").getAsString(), jsonObject.get("birth_date").getAsString(), jsonObject.get("anniversary_date").getAsString(),
                              jsonObject.get("Email").getAsString(), jsonObject.get("location_id").getAsInt(), jsonObject.get("active").getAsString(), jsonObject.get("contact_code").getAsString());
            }
          
            AddContact addcontact = new AddContact();
            msg = addcontact.addContact(add);
            //String response = "";
            if (msg.equals("Insert")) {
                  
                  //AddContact es = new AddContact();
                //System.out.println(es.stats());
                  AddContactResponse result = new AddContactResponse();
             // return new AddContactResponse(msg , result.getContact_code());
                  return new AddContactResponse(msg, "");
              //return new AddContactResponse(result.setStatus(status), result.setContactcode(contact_code));
                  
              } else if (msg.equals("Update")) {
                  //response = Utitlity.constructJSON("Success", 200, "Update");
                  return new AddContactResponse(msg, "");
                  
              }
            
            //return response;      
            return null;                  
    }
request
{
    "contact_type" : "Customer",
      "contact_category" : "General",
      "contact_sub_category" : "All",
      "contact_title" : "MRS",
      "first_name" : "Neeru",
      "middle_name" : "sal",
      "last_name" : "singh",
      "Designation": "Director",
      "mobile" : "7509010490",
      "phone": "07882325695",
      "birth_date" : "08-20-1994",
      "anniversary_date" : "08-25-2012",
      "Email" : "neer@gmail.com",
      "location_id" : 1,
      "active" : "1",
      "contact_code" :" ",
      "status" : ""
}
response
{
    "contactcode": "",
    "status": "Insert"
}
i am not receiving contact code thanks in advance.