Reading responsesedit

The Response object, either returned by the synchronous performRequest methods or received as an argument in ResponseListener#onSuccess(Response), wraps the response object returned by the http client and exposes the following information:

information about the performed request
the host that returned the response
the response status line
the response headers, which can also be retrieved by name though getHeader(String)
the response body enclosed in an org.apache.http.HttpEntity object

When performing a request, an exception is thrown (or received as an argument in ResponseListener#onFailure(Exception) in the following scenarios:

communication problem (e.g. SocketTimeoutException etc.)
a response was returned, but its status code indicated an error (not 2xx). A ResponseException originates from a valid http response, hence it exposes its corresponding Response object which gives access to the returned response.

A ResponseException is not thrown for HEAD requests that return a 404 status code because it is an expected HEAD response that simply denotes that the resource is not found. All other HTTP methods (e.g., GET) throw a ResponseException for 404 responses.