用HttpURLConnection模拟网页登录

用HttpURLConnection模拟登录某个网站，以post的方式发送请求，然后得到response的状态码是200而不是302，页面没有重定向，返回的输入流是原来的登录页面。以下是一些关键代码，麻烦给位帮忙看看，我是新手                Map<String, String> post = new HashMap<String, String>();
                //post.put("__VIEWSTATE", "dDwtMTIwMTU3OTE3Nzs7Pkpv5PWSSJQutGzQO79G0NxH9kuS");//这个值从foxbug上复制下来的
                post.put("TextBox1", "20093069***");
                post.put("TextBox2", "*****");
                post.put("RadioButtonList1", "学生");
                post.put("Button","");//
                post.put("lbLanguage", "");//这两个的值在httpfox显示都是空的
                String urlStr = "http://202.116.160.170/default2.aspx";//default2.aspx是post的方法（action="default2.aspx"）
                //设置请求头，建立连接
                URL url = new URL(urlStr);
                HttpURLConnection uc = (HttpURLConnection)url.openConnection();
                uc.setRequestMethod("POST");
                uc.setRequestProperty("Content-Type","application/x-www-form-urlencoded");
                uc.setRequestProperty("Host", "202.116.160.170");
                uc.setRequestProperty("User-Agent","Mozilla/5.0 (Windows NT 6.1; rv:11.0) Gecko/20100101 Firefox/11.0");
                uc.setRequestProperty("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");
                uc.setRequestProperty("Accept-Language", "zh-cn,zh;q=0.8,en-us;q=0.5,en;q=0.3");
                uc.setRequestProperty("Accept-Encoding", "gzip, deflate");
                uc.setRequestProperty("Connection", "keep-alive");
                uc.setRequestProperty("Referer", "http://202.116.160.170/");
                
                uc.setDoOutput(true);
                //uc.setFollowRedirects(true);
                uc.setDoInput(true);
                //将用户名、密码等以"username=XXX&password=***"的形式输出
                PrintWriter pw = new PrintWriter(uc.getOutputStream()); 
                boolean first = true;
                for(Map.Entry<String, String> pair : nameValuePairs.entrySet()){
                    if(first){
                    first = false;
                    }
                    else{
                        pw.print('&');
                    }
                    pw.print(pair.getKey());
                    pw.print('=');
                    pw.print(URLEncoder.encode(pair.getValue(), "gb2312"));//content-type里的charset=gb2312，但是把得到输入流输出到控制台后，中文乱码，试过用'UTF-8"以及"GBK"，结果一样。
                }