How to build an HttpClient interactive with remote server using Java

I need to coding an Http Client using java which interact with a stateful http server. The client needs to

1. navigate to login page and accept cookies
2. submit login page with http form field filled
3. select goods and add to shopping cart
4. submit shopping cart

I am trying to use HttpClient to implement this client. However I found even I submitted the login form, it still return the login form just like my submit is invalid. Here is my code:

HttpClient agent = new DefaultHttpClient();
agent.getParams().setParameter(ClientPNames.COOKIE_POLICY,
        CookiePolicy.RFC_2965);
CookieStore cookieStore = new BasicCookieStore();
HttpContext localContext = new BasicHttpContext();
localContext.setAttribute(ClientContext.COOKIE_STORE, cookieStore);
HttpGet httpget = new HttpG开发者_运维知识库et(site);
HttpResponse response = agent.execute(httpget, localContext);
HttpEntity entity = response.getEntity();
entity.getContent().close();

HttpPost post = new HttpPost(site + "/login.aspx");
post.getParams().setParameter("LoginControl1$ctlLoginName", "myusername");
post.getParams().setParameter("LoginControl1$ctlPassword", "mypassword");
response = agent.execute(post, localContext);
entity = response.getEntity();
String s = IO.readContentAsString(entity.getContent());
System.out.println(s);

Any idea where I am wrong? Or do you have better way to implement this?

Thanks a lot Green

Not really sure what might be wrong, but have you considered using tcpdump/Wireshark to grab the raw HTTP conversation with the server and compare what you're sending/receiving in HTTPClient with what you send/receive in your web browser when you submit the form?