Add Argument to existing Json String - json

Question

I have this situation:
More servlets set the httpservletResponse content-type to json/application.
I output my json this way:
out.write (new Gson().toJson(myObject));
where myObject, is an object and the code above provides creating a string json like using myObject structure.
Now I need to add an argument on the top of the json, because I need an argument like: "result":"okay".
Is there a way to add this without changinc myObject class?
Thanks in advance.

Answer 1

Yes. Instead of building a String using Gson#toJson() use Gson#toJsonTree() which parses the object but creates a JSON internal representation using JsonElement subclasses. You will need to cast it to a JsonObject, then add the new property and finally write it to the output stream.
Code example:
package net.sargue.gson;
import com.google.gson.Gson;
import com.google.gson.JsonObject;
public class SO36837061 {
public static class MyClass {
int a = 1;
String b = "salut";
}
public static void main(String[] args) {
MyClass myObject = new MyClass();
JsonObject jsonObject = (JsonObject) new Gson().toJsonTree(myObject);
jsonObject.addProperty("result", "okay");
String json = new Gson().toJson(jsonObject);
System.out.println("json = " + json);
}
}
Output:
json = {"a":1,"b":"salut","result":"okay"}