java HttpClient模拟登陆知乎问答网站，获取不到cookie

public static void main(String[] args){

	String loginUrl = "http://www.zhihu.com";

	String username = "XXXXXXXXXXXX";

	String password = "XXXXXXXXXXXX";

	String htmlGetSource = "";

	HttpClient httpClient = new DefaultHttpClient();



	httpClient.getParams().setParameter(CoreProtocolPNames.USER_AGENT, "Mozilla/5.0 (X11; U; Linux i686; zh-CN; rv:1.9.1.2) Gecko/20090803 Fedora/3.5.2-2.fc11 Firefox/3.5.2");

	//获取登录框的隐含参数 type="hidden" name="_xsrf"

	try {

		HttpGet httpGet = new HttpGet(loginUrl);

		HttpResponse response = httpClient.execute(httpGet);

		HttpEntity entity = response.getEntity();

		if(entity!=null){

			InputStream in = entity.getContent();

			String str = "";

			BufferedReader br = new BufferedReader(new InputStreamReader(in,"UTF-8"));

			while((str=br.readLine())!=null){

				htmlGetSource += str+"\n";

			}

		}

	} catch (ClientProtocolException e1) {

		e1.printStackTrace();

	} catch (IOException e1) {

		e1.printStackTrace();

	}

	//应用JsoupHtml解析包解析html包含参数

	Document doc = Jsoup.parse(htmlGetSource);

	Element formContent = null;

	Element inputContent = null;

	String actionStr = "";

	String _xsrf="";

	String checked = "on";

	formContent  = doc.select("form[method=post]").first();

	inputContent = doc.select("input[type=hidden]").first();

	actionStr = formContent.attr("action");

	_xsrf = inputContent.attr("value");

	System.out.println(actionStr);



	HttpPost httpPost = new HttpPost(actionStr);

	HttpResponse response;

	//请求Header

	httpPost.setHeader("(Request-Line)","POST /login HTTP/1.1");

	httpPost.setHeader("User-Agent","Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/20100101 Firefox/15.0.1");  

	httpPost.setHeader("Referer", "http://www.zhihu.com/");  

	httpPost.setHeader("Content-Type", "application/x-www-form-urlencoded");  

	httpPost.setHeader("Accept-Language","zh-cn,zh;q=0.8,en-us;q=0.5,en;q=0.3");

	httpPost.setHeader("Accept-Encoding","gzip, deflate");

	httpPost.setHeader("Accept","text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");

	httpPost.setHeader("Connection","keep-alive");

	//POST参数

	List<NameValuePair> nvps = new ArrayList<NameValuePair>();

	nvps.add(new BasicNameValuePair("_xsrf", _xsrf));

	nvps.add(new BasicNameValuePair("email", username));

	nvps.add(new BasicNameValuePair("password", password));

	nvps.add(new BasicNameValuePair("rememberme", "on"));

	

	try {

		httpPost.setEntity(new UrlEncodedFormEntity(nvps,HTTP.UTF_8));

		response = httpClient.execute(httpPost);

		//Header[] headers = response.getAllHeaders();

		//for(Header h:headers){

		//	System.out.println(h);

		//}

		//得到cookie  

		String set_cookie = response.getFirstHeader("Set-Cookie").getValue();

		System.out.println(set_cookie);

	} catch (UnsupportedEncodingException e) {

		e.printStackTrace();

	} catch (IOException e) {

		e.printStackTrace();

	} finally {

		httpPost.abort();

	}

}