java创建用户连接数据库，用数据库密码和账号登录，登录成功后进入showAllProducts页面，写出dao,service,se

rvlet的代码。

首先是DAO层的代码，用于访问数据库：

public class ProductDAO {
    private final String url = "jdbc:mysql://localhost/mydatabase";
    private final String username = "myusername";
    private final String password = "mypassword";

    public List<Product> getAllProducts() {
        List<Product> products = new ArrayList<>();
        try (Connection conn = DriverManager.getConnection(url, username, password)) {
            String sql = "SELECT * FROM products";
            try (Statement stmt = conn.createStatement()) {
                try (ResultSet rs = stmt.executeQuery(sql)) {
                    while (rs.next()) {
                        Product product = new Product();
                        product.setId(rs.getInt("id"));
                        product.setName(rs.getString("name"));
                        product.setPrice(rs.getDouble("price"));
                        products.add(product);
                    }
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return products;
    }
}

接着是Service层的代码，用于处理业务逻辑：

public class ProductService {
    private ProductDAO productDAO = new ProductDAO();

    public List<Product> getAllProducts() {
        return productDAO.getAllProducts();
    }
}

最后是Servlet层的代码，用于接收请求和返回响应：

@WebServlet("/showAllProducts")
public class ShowAllProductsServlet extends HttpServlet {
    private ProductService productService = new ProductService();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        List<Product> products = productService.getAllProducts();
        req.setAttribute("products", products);
        req.getRequestDispatcher("/WEB-INF/jsp/showAllProducts.jsp").forward(req, resp);
    }
}

在这个例子中，Servlet接收GET请求，调用Service层的方法获取所有的产品，然后将其存储在请求属性中，并将请求转发到JSP页面以显示所有产品的列表。