session与severlet实现数据库连接事例

以下是一个使用Servlet和Session实现数据库连接的示例：

1. 创建一个名为`DatabaseConnection`的Java类，该类用于连接数据库并执行SQL查询。

public class DatabaseConnection {
    private Connection conn;

    public DatabaseConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/mydb";
            String user = "root";
            String password = "root";
            conn = DriverManager.getConnection(url, user, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public ResultSet executeQuery(String sql) throws SQLException {
        Statement stmt = conn.createStatement();
        return stmt.executeQuery(sql);
    }
}

2. 创建一个名为`LoginServlet`的Servlet类，该类用于处理用户登录请求，并从数据库中验证用户。

public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        DatabaseConnection conn = new DatabaseConnection();
        String sql = "SELECT * FROM users WHERE username='" + username + "' AND password='" + password + "'";
        ResultSet rs = null;

        try {
            rs = conn.executeQuery(sql);

            if (rs.next()) {
                HttpSession session = request.getSession();
                session.setAttribute("username", username);
                response.sendRedirect("welcome.jsp");
            } else {
                response.sendRedirect("login.jsp");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

3. 创建一个名为`WelcomeServlet`的Servlet类，该类用于处理用户登录后的请求，并从Session中获取用户名。

public class WelcomeServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        String username = (String) session.getAttribute("username");

        response.getWriter().println("Welcome, " + username + "!");
    }
}

在这个示例中，`LoginServlet`从数据库验证用户，并将用户名存储在Session中。`WelcomeServlet`从Session中获取用户名，并在响应中返回欢迎消息。通过这种方式，Servlet和Session共同实现了数据库连接的功能。