Use Square's converter by adding this to your build.gradle:
compile 'com.squareup.retrofit:converter-jackson:1.9.0'
Afterwards you can activate it by adding .setConverter(new JacksonConverter()) to your RestAdapter builder.
.setConverter(new JacksonConverter())
RestAdapter
with new versions of OkHTTP it seems its done with:
Retrofit retrofit = new Retrofit.Builder() .baseUrl(API_URL) .addConverterFactory(JacksonConverterFactory.create()) .build();