Parse JSON file using GSON

Question

I want to parse this JSON file in JAVA using GSON :

{
    "descriptor" : {
        "app1" : {
            "name" : "mehdi",
            "age" : 21,
            "messages": ["msg 1","msg 2","msg 3"]
        },
        "app2" : {
            "name" : "mkyong",
            "age" : 29,
            "messages": ["msg 11","msg 22","msg 33"]
        },
        "app3" : {
            "name" : "amine",
            "age" : 23,
            "messages": ["msg 111","msg 222","msg 333"]
        }
    }
}

but I don't know how to acceed to the root element which is : descriptor, after that the app3 element and finally the name element.

I followed this tutorial http://www.mkyong.com/java/gson-streaming-to-read-and-write-json/, but it doesn't show the case of having a root and childs elements.

Answer 1

Imo, the best way to parse your JSON response with GSON would be creating classes that "match" your response and then use Gson.fromJson() method.
For example:

class Response {
    Map<String, App> descriptor;
    // standard getters & setters...
}

class App {
  String name;
  int age;
  String[] messages;
  // standard getters & setters...
}

Then just use:

Gson gson = new Gson();
Response response = gson.fromJson(yourJson, Response.class);

Where yourJson can be a String, any Reader, a JsonReader or a JsonElement.

Finally, if you want to access any particular field, you just have to do:

String name = response.getDescriptor().get("app3").getName();

You can always parse the JSON manually as suggested in other answers, but personally I think this approach is clearer, more maintainable in long term and it fits better with the whole idea of JSON.