如何用java写一个12306抢票小程序

写一个12306抢票小程序，需要以下步骤：

1. 登录12306网站并获取会话cookie
2. 查询车票信息并获取列车信息
3. 提交订单并获取订单信息
4. 验证订单信息并确认订单
5. 完成支付流程

下面是一个简单的示例程序：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

public class TrainTicket {

    private static final String LOGIN_URL = "https://kyfw.12306.cn/otn/login/init";
    private static final String QUERY_URL = "https://kyfw.12306.cn/otn/leftTicket/query";
    private static final String SUBMIT_URL = "https://kyfw.12306.cn/otn/leftTicket/submitOrderRequest";
    private static final String CHECK_URL = "https://kyfw.12306.cn/otn/confirmPassenger/checkOrderInfo";
    private static final String PAY_URL = "https://kyfw.12306.cn/otn/pay/payGateway";

    private static final Map<String, String> headers = new HashMap<>();
    private static final String USER_AGENT = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36";

    public static void main(String[] args) throws Exception {
        // 登录12306网站并获取会话cookie
        String cookie = login();

        // 查询车票信息并获取列车信息
        String trainInfo = queryTrain(cookie);

        // 提交订单并获取订单信息
        String orderInfo = submitOrder(cookie, trainInfo);

        // 验证订单信息并确认订单
        String token = checkOrder(cookie, orderInfo);

        // 完成支付流程
        payOrder(cookie, token);
    }

    private static String login() throws Exception {
        URL url = new URL(LOGIN_URL);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setRequestProperty("User-Agent", USER_AGENT);
        BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        String line;
        String cookie = null;
        while ((line = in.readLine()) != null) {
            if (line.startsWith("Set-Cookie:")) {
                cookie = line.split(";")[0].split(": ")[1];
            }
        }
        in.close();
        return cookie;
    }

    private static String queryTrain(String cookie) throws Exception {
        String date = "2022-01-01";
        String from = "BJP";
        String to = "SHH";
        URL url = new URL(QUERY_URL + "?" + "leftTicketDTO.train_date=" + date +
                "&leftTicketDTO.from_station=" + from +
                "&leftTicketDTO.to_station=" + to +
                "&purpose_codes=ADULT");
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setRequestProperty("User-Agent", USER_AGENT);
        conn.setRequestProperty("Cookie", cookie);
        BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        String line;
        StringBuilder result = new StringBuilder();
        while ((line = in.readLine()) != null) {
            result.append(line);
        }
        in.close();
        return result.toString();
    }

    private static String submitOrder(String cookie, String trainInfo) throws Exception {
        // TODO: 提交订单
        return null;
    }

    private static String checkOrder(String cookie, String orderInfo) throws Exception {
        // TODO: 验证订单信息并确认订单
        return null;
    }

    private static void payOrder(String cookie, String token) throws Exception {
        // TODO: 完成支付流程
    }
}

注意，这只是一个简单的示例程序，实际的抢票流程可能比这个复杂得多。此外，12306网站有反爬虫机制，需要注意一些细节，比如请求频率等。