Google App Engine is one of the supported Java environments for the Google HTTP Client Library for Java.
The JSON data model is optimized for efficient memory usage that minimizes parsing and serialization time. Only the fields you need are actually parsed when processing a JSON response.
For your JSON parser, we recommend JacksonFactory, which is based on the popular Jackson library. It is considered the fastest in terms of parsing/serialization. You can also use GsonFactory, which is based on the Google GSON library. It is a lighter-weight option (smaller size) that is fairly fast, but it is not quite as fast as Jackson.