How do I get the text from this JSON file using GSON?

Question

Im using GSON to parse this JSON file:

{
    "database" : {
        "source" : "google",
        "items" : [
            {"title" : "hello world",
            "id" : "id_hello_world"},

            {"title" : "goodbye world",
            "id" : "id_goodbye_world"}
        ]
    }
}

Which ive read into String jsonLine

Im trying to parse it and output all the values but im getting a ClassCastException at the

JsonObject source = database.getAsJsonObject("source") line.

I think im searching for the data wrong. Im using this to search and output:

        JsonElement jelement = new JsonParser().parse(jsonLine);

        JsonObject jobject = (JsonObject) jelement;

        JsonObject database = jobject.getAsJsonObject("database"); //Get Database
        JsonObject source = database.getAsJsonObject("source"); //Get Source
        System.out.println("Source: " + source.toString()); //Print source

        JsonArray items = database.getAsJsonArray("items"); //Get items array

        for(int i=0; i< items.size(); i++){ //for every item
            JsonObject item = (JsonObject) items.get(i); //Select item i
            JsonObject title = (JsonObject) item.getAsJsonObject("title");
            JsonObject id = (JsonObject) item.getAsJsonObject("id");
            System.out.println("Item " + i + " title : " + title.toString() + ", id : " + id.toString());
        }

If someone could correct my code that would be perfect. I know there are other simpler ways to do this using GSON.fromJSON(jsonLine, Wrapper.class) but im trying to learn to do it this way too. Thanks for the help!

Answer 1

Before you are going to use Gson method, create your template structure:

class Item{
  private String item = "";
  private String id = ""; // for sure you can use 'int'
}

public class DataBase{
  private  List<Item> items = null;
  private String source = "";
}

Now your main class:

public class YourClass{
 private DataBase database = "";

 ....

 database  = gson.fromJson(yourString, YourClass.class);

...
}

Don't forget try/catch wrapper

Enjoy

Answer 2

use JsonPrimitive instead of JsonObject . (it must be internal bug of GSON, because, trying to convert JsonPrimitive to JsonObject was impossible, as far as the version of GSON 2.2.3) So, your code comes like this:

JsonElement jelement = new JsonParser().parse(jsonLine);

JsonObject jobject = (JsonObject) jelement;

JsonObject database = jobject.getAsJsonObject("database"); // Get
                                                            // Database
JsonPrimitive source = database.getAsJsonPrimitive("source"); // Get
                                                                // Source
System.out.println("Source: " + source.toString()); // Print source

JsonArray items = database.getAsJsonArray("items"); // Get items array

for (int i = 0; i < items.size(); i++) { // for every item
    JsonObject item = (JsonObject) items.get(i); // Select item i
    JsonPrimitive title = item.getAsJsonPrimitive("title");
    JsonPrimitive id = item.getAsJsonPrimitive("id");
    System.out.println("Item " + i + " title : " + title.toString()
            + ", id : " + id.toString());
}

As Maxim Shoustin showed, creating template will be good solution for it.