@WebServlet("/login.do")
public class LoginServlet extends javax.servlet.http.HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String aid = req.getParameter("aid");
    }

}

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.getSession().setAttribute(String key, Object value);
}

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    resp.sendRedirect("index.jsp");
}

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.setCharacterEncoding("utf-8");
    resp.setContentType("text/html;charset=utf-8");
}

username=root
password=123456
url=jdbc:mysql://localhost:3306/vltest?useSSL=false&serverTimezone=UTC&characterEncoding=utf-8
driver=com.mysql.cj.jdbc.Driver

public class ConnectionUtil {

    private static String username, password, url, driver;
    private static final String path = "*********.properties";

    static {
        try {
            getParam(path);
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, username, password);
    }

    /**
     * 通过配置文件读取一些配置的值
     */
    private static void getParam(String path) throws IOException {
        // 获取类装载器
        ClassLoader classLoader = ConnectionUtil.class.getClassLoader();
        // 通过类加载器来加载配置文件
        InputStream inputStream = classLoader.getResourceAsStream(path);
        // 配置文件是properties文件, 所以创建一个Properties对象
        Properties properties = new Properties();
        // 使用properties对象去读取配置文件的文件流
        properties.load(inputStream);

        // 通过指定的key来获取对应的value
        username = properties.getProperty("username");
        password = properties.getProperty("password");
        url = properties.getProperty("url");
        driver = properties.getProperty("driver");
    }

}

public static String getSomethingByObject(Object o) {
    String sql = "";
    Connection connection = null;
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
    try {
        connection = ConnectionUtil.getConnection();
        preparedStatement = connection.prepareStatement(sql);
        preparedStatement.setString(1, Object o);
        resultSet = preparedStatement.executeQuery();
    
    
        resultSet.close();
        preparedStatement.close();
        connection.close();
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        try {
            if (resultSet != null) resultSet.close();
            if (preparedStatement != null) preparedStatement.close();
            if (connection != null) connection.close();
        } catch (SQLException e) {
        }
    }
}

Article article = ArticleDao.getArticleByAid(aid);
req.getSession().setAttribute("article",article);
resp.sendRedirect("info.jsp");