从登录过程中获取会话信息

private static final String loginUrl = "http://42.120.50.206/apr/login.php";
private String sessionId;
public boolean login(String username, String password) {
                                               
        Map<String, String> params = new HashMap<String, String>();
        params.put("username", username);
        params.put("password", password);
                                               
        HttpURLConnection connection = null;
                                       
        try {
            connection = doPost2(loginUrl, params);
            if (connection == null) {
                return false;
            }
                                           
            String key = "";
                                           
            if (connection != null) {
                for (int i = 1; (key = connection.getHeaderFieldKey(i)) != null; i++) {
                    //System.out.println("key: " + key);
                    if (key.equalsIgnoreCase("set-cookie")) {
                        sessionId = connection.getHeaderField(key);
                        sessionId = sessionId.substring(0, sessionId.indexOf(";"));
                        //System.out.println("sessionId: " + sessionId);
                    }
                 }
                                               
                InputStream is = connection.getInputStream();
                String result = getResult(is);
                System.out.println("result: " + result);
                                               
                if (sessionId != null) {
                    return true;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (connection != null) {
                connection.disconnect();
            }  
        }
                                       
        return false;
    }

public HttpURLConnection doPost2(String urlStr, Map<String, String> params) throws IOException {
        StringBuilder sb = new StringBuilder();
                                    
        for(Map.Entry<String, String> param : params.entrySet()) {
            sb.append(param.getKey()).append("=").append(param.getValue()).append("&");
        }
                                    
        int len = sb.length();
        if (len > 0) {
            sb.deleteCharAt(len - 1);
        }
                                    
        String args = sb.toString();
        //System.out.println("args: " + args);
        return doPost2(urlStr, args);
    }
                                
    /**
     * @param args
     * @throws IOException
     * @throws UnsupportedEncodingException
     */
    public HttpURLConnection doPost2(String urlStr, String args) throws IOException {
                                    
        URL url = null;
        try {
            url = new URL(urlStr);
        } catch (MalformedURLException e) {
            e.printStackTrace();
            return null;
        }
                                    
        HttpURLConnection connection = (HttpURLConnection)url.openConnection();  
        // 模仿浏览器，可有可无
        connection.setRequestProperty("User-Agent", "Mozilla/5.0 (X11; Linux i686; rv:7.0.1) Gecko/20100101 Firefox/7.0.1");
        // 这一行很关键，登录需要这一行
        connection.setInstanceFollowRedirects(false);
        connection.setConnectTimeout(10000);
                                    
                                    
        /**
         * 然后把连接设为输出模式。URLConnection通常作为输入来使用，比如下载一个Web页。
         * 通过把URLConnection设为输出，你可以把数据向你个Web页传送。下面是如何做：
         */ 
        connection.setDoOutput(true);  
        //connection.setRequestMethod("POST");
                                    
        /**
         * 最后，为了得到OutputStream，简单起见，把它约束在Writer并且放入POST信息中，例如： ...
         */ 
        OutputStreamWriter out = new OutputStreamWriter(connection.getOutputStream(), "UTF-8");  
        out.write(args); //向页面传递数据。post的关键所在！  
        // remember to clean up  
        out.flush();  
        out.close();  
                                    
        return connection;
    }

private static String getResult(InputStream is) throws IOException {
    StringBuilder sb = new StringBuilder();
                           
    BufferedReader br = new BufferedReader(new InputStreamReader(   
            is));   
                           
    String line = null;
    while ((line = br.readLine()) != null) {   
        sb.append(line).append("\r\n");   
    }   
                           
    return sb.toString();
}