Depending on which public version you are using, you might try DefaultHttpResponseFactory . This is the way the library creates some of the answers within itself, so it may or may not serve your purposes.
import org.apache.http.HttpStatus;
import org.apache.http.HttpResponse;
import org.apache.http.HttpResponseFactory;
import org.apache.http.HttpVersion;
import org.apache.http.impl.DefaultHttpResponseFactory;
import org.apache.http.message.BasicStatusLine;
HttpResponseFactory factory = new DefaultHttpResponseFactory();
HttpResponse response = factory.newHttpResponse(new BasicStatusLine(HttpVersion.HTTP_1_1, HttpStatus.SC_OK, null), null);