Convert JSON to a Map

Passing Map.class

In general, Gson provides the following API in its Gson class to convert a JSON string to an object:

public <T> T fromJson(String json, Class<T> classOfT) throws JsonSyntaxException;
  • classOfT: is the class of the object which we intend the JSON to parse into.
  • If there are duplicate keys, though, coercion will fail and it will throw a JsonSyntaxException.

Using TypeToken

To overcome the problem of type-erasure for the generic types, Gson has an overloaded version of the API:

public <T> T fromJson(String json, Type typeOfT) throws JsonSyntaxException;

We can construct a Map with its type parameters using Gson’s TypeToken. The TypeToken class returns an instance of ParameterizedTypeImpl that preserves the type of the key and value even at runtime

Using Custom JsonDeserializer

When we need fine-grained control over the construction of our Map object, we can implement a custom deserializer of type JsonDeserializer<Map>.

  • StringDateMapDeserializer

Results

  • ConvertJsonToMapTest