Add
compile 'com.squareup.retrofit:converter-gson:2.0.0-beta2' to your build.gradlefile and get the dependency resolved or add corresponding jars to your bulid path.then use
GsonConverterFactory.create() to get the Converter FactoryTry this with retrofit 2:
compile 'com.squareup.retrofit2:converter-gson:2.0.0-beta4'