gson intrepret specific field as capitalized

Question

I have a class with some fields, e.g.

public class Message {

    public Enum Type {
        TEXT,
        PICTURE;
    }

    private Type type;
    private String text;
    private int id;
}

Let's say I have a json like the following

[ { "id" : "1",
    "data" : "hello",
    "type" : "text",
  },
  { "id" : "2",
    "data" : "<someImageUrl>",
    "type" : "picture",
  },
]

I can easily deserialize it by calling

Gson gson = new Gson();
ArrayList<Message> messages = gson.fromJson(jsonResult, new TypeToken<List<Message>>() {}.getType());

Cool. Unfortunately, the Type field remains null, because of the casing difference between the json object and the defined instances in the enum. How can I alter gson's behaviour so that it will interpret json Type objects as capitalized.

Potential workaround I have thought of:

• assign ordinal values to the enum type that will match what's given in the json (i.e. TEXT("text")
• split the json result by the delimiting character "},"
• replace all occurences of -someEnumType- with -SOMEENUMTYPE-

something like

public enum Type {
    TEXT("text"),
    PICTURE("picture");

    private final String value

    private MessageType(String value) {
        this.value = value;
    }

    public String getValue() {
        return value
    }
}
...

   String[] jsonResultSplit = StringUtils.split(jsonResult, "},") 
   for (String jsonMessage : jsonResultSplit) {
        for (MessageType messageType : MessageType.values()) {
            if (jsonMessage.contains("\"type:\" : \"" + messageType.getValue() + "\"")) {
                jsonMessage.replace(
                        "\"type:\" : \"" + messageType.getValue() + "\"",
                        "\"type:\" : \""
                                + StringUtils.capitalize(messageType.getValue() + "\""));
            }
        }
    }
    jsonResult = StringUtils.join(jsonResultSplit);
    Gson gson = new Gson();
    ArrayList<Message> messages = gson.fromJson(jsonResult, new TypeToken<List<Message>>() {}.getType());

However this seems kind of hacky, and the string will be split incorrectly if a message contains "}," or something.

Answer 1

Simplest way is to use @SerializedName annotation for your Enum.

public Enum Type {
    @SerializedName("text")
    TEXT,

    @SerializedName("picture")
    PICTURE
}

@SerializedName can be used not only for capitalization but also to change name of your enums or variables, for example

public enum Gender {
    @SerializedName("boy")
    MALE,

    @SerializedName("girl")
    FEMALE
}

Reference

Also as @Sotirios suggested, you need to annotate text to map json key with your variable.

 @SerializedName("data")
 private String text;

You can now deserialize your json using Gson as earlier

Gson gson = new Gson();
ArrayList<Message> messages = gson.fromJson(jsonResult, new TypeToken<List<Message>>() {}.getType());

Hope this helps...

Answer 2

You'll have to register your own TypeAdapter to do the conversion

Gson gson = new GsonBuilder().registerTypeAdapter(Type.class,
            new TypeAdapter<Type>() {

                @Override
                public void write(JsonWriter out, Type value)
                        throws IOException {
                    out.value(value.name().toLowerCase());
                }

                @Override
                public Type read(JsonReader in) throws IOException {
                    return Type.valueOf(in.nextString().toUpperCase());
                }
            }).create();

---

Note that you should also annotate

private String text;

with @SerializedName("data") as it doesn't match the JSON name.

"data" : "hello",