Parsing JSON with Gson

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The example shows parsing a JSON object using the Gson library from Google.

Parsing objects:

class Robot {
    //OPTIONAL - this annotation allows for the key to be different from the field name, and can be omitted if key and field name are same . Also this is good coding practice as it decouple your variable names with server keys name 
    private String version;

    private int age;
    private String name;
    // optional : Benefit it allows to set default values and retain them, even if key is missing from Json response. Not required for primitive data types. 

    public Robot{
       version = "";
       name = "";

Then where parsing needs to occur, use the following:

String robotJson = "{
                        \"version\": \"JellyBean\",
                        \"age\": 3,
                        \"robotName\": \"Droid\"

Gson gson = new Gson();
Robot robot = gson.fromJson(robotJson, Robot.class);

Parsing a list:

When retrieving a list of JSON objects, often you will want to parse them and convert them into Java objects.

The JSON string that we will try to convert is the following:

  "owned_dogs": [
      "name": "Ron",
      "age": 12,
      "breed": "terrier"
      "name": "Bob",
      "age": 4,
      "breed": "bulldog"
      "name": "Johny",
      "age": 3,
      "breed": "golden retriever"

This particular JSON array contains three objects. In our Java code we’ll want to map these objects to Dog objects. A Dog object would look like this:

private class Dog {
    public String name;
    public int age;

    public String breedName;

To convert the JSON array to a Dog[]:

Dog[] arrayOfDogs = gson.fromJson(jsonArrayString, Dog[].class);

Converting a Dog[] to a JSON string:

String jsonArray = gson.toJson(arrayOfDogs, Dog[].class);

To convert the JSON array to an ArrayList<Dog> we can do the following:

Type typeListOfDogs = new TypeToken<List<Dog>>(){}.getType();
List<Dog> listOfDogs = gson.fromJson(jsonArrayString, typeListOfDogs);

The Type object typeListOfDogs defines what a list of Dog objects would look like. GSON can use this type object to map the JSON array to the right values.

Alternatively, converting a List<Dog> to a JSON array can be done in a similar manner.

String jsonArray = gson.toJson(listOfDogs, typeListOfDogs);

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