I am using the Apache HttpClient for some work I am doing at the office.
It is a really cool utility to perform web based work. A common
requirement of such work is to use authentication.
The default behavior of the HttpClient is to try and connect to the resource and read the response. If the response is a
401 Unauthorized,
the client sends the request again using the credentials that are set
in the client. This results in an unnecessary double posting of the
request. It is however compliant with
RFC2616 Section 10.4.2 which describes this behavior.
In the previous version of the client (3.x), you could set the preemptive authentication with the code below:
httpClient.getParams().setAuthenticationPreemptive(true);
However, version 4.x does not support this convenient arrangement. There
is a more flexible arrangement using interceptors. The client supports
interceptors on both the request, and the response. The use of
interceptors makes the code a little more complex, but the flexibility
of using multiple interceptors, and ordering them makes up for the
additional code required.
I can not provide an example of my code since it was something I created
for work, but here are two examples. The first is complete, and the
second is simply an example.
There is an additional post on stackoverflow which indicates you may be
able to use a simple addition to the header. This may work for simple
clients, but it is not as flexible as the interceptor form.
I have not tested the code, but have included
Adam Batkin's code snippet below.
String username = ...
String password = ...
UsernamePasswordCredentials creds = new UsernamePasswordCredentials(username, password);
HttpRequest request = ...
request.addHeader(new BasicScheme().authenticate(creds, request));
