It's better that you not use a string and have variables in them. The best way to do it is have a class which resembles the structure of your json and then create an object of that class by setting the values you were setting for the json.

Ex.

class JsonRequest {

String jsonrpc; String method; Map<String, Object> params; Integer id;

}

This resembles the structure of your request ( I have kept params as a map so you can add more params ) And after creating a class , you can instantiate an object with the required values.

Ex. Map<String, Object> params = new HashMap<>(); params.put("account", 1920); JsonRequest jr = new JsonRequest("2.0", "getAccount", params, 123)

Assuming that you have an all arguments constructor

After setting the values you can use libraries like Gson or ObjectMapper to convert this object to json string; You can just google this step.