1. To use library you should add it in your build.gradle:

       compile 'org.itishka.gson-flatten:gson-flatten:0.7'

2. Then register it in your gson builder:

   final Gson gson = new GsonBuilder()
             .registerTypeAdapterFactory(new FlattenTypeAdapterFactory())
             .create();

3. Define your class and use @Flatten annotation to get data from embedded objects. For example class

   class Weather {
     @Flatten("temperature::min")
     int min_temperture;
     @Flatten("temperature::max")
     int max_temperture;
   }

   will be filled with data from json

   {
     "temperature": {
        "min": -273,
        "max": 1000
     }
   }

4. Then just parse or serialize json as your usually do:

     String json = gson.toJson(weather);
     Weather weather2 = gson.fromJson(json, Weather.class);

• You can skip field name if it equlas in inner object and outer one. E.g.:

class Weather {
    @Flatten("temperature::")
    int min;
    @Flatten("temperature::")
    int max;
}

• You can get array items as well (tnx @tominsam):

class SomeClass {
    @Flatten("some_array::0")
    int first_value;
}

• If you are using Gson 2.7 with some FieldNamingStrategies with and gson-flatten 0.6 you do not need to do anything more!

With previous versions of gson and gson-flatten you should provide FieldNamingStrategy to FlattenTypeAdapterFactory:

final Gson gson = new GsonBuilder()
          .setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
          .registerTypeAdapterFactory(new FlattenTypeAdapterFactory(FieldNamingPolicy.UPPER_CAMEL_CASE))
          .create();

Based on https://github.com/noties/Flatten

Gson-flatten is released under LGPL 3.0 license