I read somwhere that goole just allowed only fetch. Does that mean it's impossible to integrate org.apache.http.client.HttpClient in google appe engine ?
If not, are there an alternative for using existing librairies using org.apache.http.client.HttpClient on google app engine ?
So the answer is not. You need to use google fetch library.
The only supported HTTP transport is UrlFetchTransport based on URL Fetch Java API in the Google App Engine SDK
Do not try ApacheHttpTransport because it will definitely fail on Google App Engine.