如何正确使用CookieManager和HttpURLConnection？

Question

我正在开发一个小程序，在基于会话的屏幕上通过HttpUrlConnection执行登录，保存cookie并使用保存的cookie转到另一个页面。我的代码如下所示：

public class LoginConnection {

    private final String USER_AGENT = "Mozilla/5.0";

    private CookieStore cookieJar;

    public static void main(String[] args) throws Exception {

        LoginConnection http = new LoginConnection();
        http.sendPost();
        http.sendGet();
    }

    public LoginConnection() {
        CookieManager manager = new CookieManager();
        CookieHandler.setDefault(manager);
        cookieJar = manager.getCookieStore();
    }

    private void sendPost() throws Exception {

        String params = "login=username&password=passwd";

        URL url = new URL("http://www.domain.com/login");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
        connection.setRequestProperty("User-Agent", USER_AGENT);
        connection.setRequestProperty("Accept-Language", "pt-BR,pt;q=0.8,en-US;q=0.6,en;q=0.4");

        // Send post request
        connection.setDoOutput(true);
        DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
        wr.writeBytes(params);
        wr.flush();
        wr.close();

        // send request
        DataOutputStream dos = new DataOutputStream(connection.getOutputStream());
        dos.writeBytes(params);
        dos.flush();
        dos.close();

        BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line, response = "";
        while ((line = in.readLine()) != null) {
            response += line + "\n";
        }
        in.close();

        String headerName = null;
        for (int i = 1; (headerName = connection.getHeaderFieldKey(i)) != null; i++) {
            if (headerName.equals("Set-Cookie")) {
                String cookie = connection.getHeaderField(i);
                cookie = cookie.substring(0, cookie.indexOf(";"));
                String cookieName = cookie.substring(0, cookie.indexOf("="));
                String cookieValue = cookie.substring(cookie.indexOf("=") + 1, cookie.length());

                HttpCookie httpCookie = new HttpCookie(cookieName, cookieValue);
                httpCookie.setDomain("http://www.domain.com/");
                httpCookie.setPath("/");
                httpCookie.setVersion(0);

                cookieJar.add(new URI("http://www.domain.com/"), httpCookie);
            }
        }

        // show cookies (sessionid)
        System.out.println("CookieHandler retrieved cookie: " + cookieJar.getCookies().get(0).toString());
        // print result
        System.out.println(response.toString().replaceAll("\\s+", " "));
    }

    // HTTP GET request
    private void sendGet() throws Exception {

        URL url = new URL("http://www.domain.com/profile");
        HttpURLConnection con = (HttpURLConnection) url.openConnection();
        con.setRequestMethod("GET");

        // add request header
        con.setRequestProperty("User-Agent", USER_AGENT);
        con.setRequestProperty("Cookie", cookieJar.getCookies().get(0).toString());

        con.getContent();

        BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
        String line, response = "";
        while ((line = in.readLine()) != null) {
            response += line + "\n";
        }
        in.close();

        // show cookies (sessionid)
        System.out.println("CookieHandler retrieved cookie: " + cookieJar.getCookies().get(0).toString());
        // print result
        System.out.println(response.toString().replaceAll("\\s+", " "));
    }

}

问题是即使发送cookie，服务器也会返回登录页面。有人能帮助我吗？