1. 创建一个JSP页面buy.jsp，实现一个查询蛋糕信息的按钮和表格。当用户点击查询蛋糕信息按钮时，通过axios向后端发送一个请求，后端从数据库中查询所有蛋糕信息并将结果返回给前端。前端通过axios接收后端传回的数据，并将数据填充到表格中。 2. 在页面下方添加一个购物车区域，包括一个蛋糕列表和一个购买按钮。当用户复选蛋糕后，将其添加到蛋糕列表中。当用户点击购买按钮时，通过axios向后端发送一个请求，提交所购买的蛋糕信息。后端接收请求后，更新数据库中的剩余蛋糕数量，并将购买的蛋糕信息返回给前端。前端通过axios接收后端传回的数据，并将其填充到购物车列表中。 3. 在后端使用连接池管理数据库连接，并使用JDBC API连接数据库。实现查询所有蛋糕信息、更新蛋糕数量等操作。

好的，下面是一个简单的实现思路和代码示例。

1. 在buy.jsp中添加以下HTML代码：

<button onclick="queryCakes()">查询蛋糕信息</button>
<table id="cakeTable">
  <tr>
    <th>蛋糕名称</th>
    <th>蛋糕价格</th>
    <th>蛋糕数量</th>
  </tr>
</table>

<div>
  <h3>购物车</h3>
  <table id="cartTable">
    <tr>
      <th>蛋糕名称</th>
      <th>蛋糕价格</th>
      <th>蛋糕数量</th>
    </tr>
  </table>
  <button onclick="buyCakes()">购买</button>
</div>

2. 在buy.jsp中添加以下JavaScript代码：

function queryCakes() {
  axios.get('/cakes').then(response => {
    const cakes = response.data;
    const table = document.getElementById('cakeTable');
    cakes.forEach(cake => {
      const row = table.insertRow();
      row.insertCell().textContent = cake.name;
      row.insertCell().textContent = cake.price;
      row.insertCell().textContent = cake.quantity;
    });
  });
}

const cart = [];

function addToCart(name, price, quantity) {
  const item = { name, price, quantity };
  cart.push(item);
}

function buyCakes() {
  axios.post('/buy', cart).then(response => {
    const boughtCakes = response.data;
    const table = document.getElementById('cartTable');
    boughtCakes.forEach(cake => {
      const row = table.insertRow();
      row.insertCell().textContent = cake.name;
      row.insertCell().textContent = cake.price;
      row.insertCell().textContent = cake.quantity;
    });
  });
}

3. 在后端使用连接池管理数据库连接，并使用JDBC API连接数据库。在Servlet中添加以下代码：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

import com.fasterxml.jackson.databind.ObjectMapper;

public class CakeServlet extends HttpServlet {
  private DataSource dataSource;

  @Override
  public void init() throws ServletException {
    try {
      Context context = new InitialContext();
      dataSource = (DataSource) context.lookup("java:comp/env/jdbc/cake");
    } catch (NamingException e) {
      throw new ServletException("Unable to initialize DataSource", e);
    }
  }

  @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    try (Connection connection = dataSource.getConnection()) {
      PreparedStatement statement = connection.prepareStatement("SELECT * FROM cakes");
      ResultSet resultSet = statement.executeQuery();
      List<Cake> cakes = new ArrayList<>();
      while (resultSet.next()) {
        Cake cake = new Cake();
        cake.setId(resultSet.getInt("id"));
        cake.setName(resultSet.getString("name"));
        cake.setPrice(resultSet.getDouble("price"));
        cake.setQuantity(resultSet.getInt("quantity"));
        cakes.add(cake);
      }
      ObjectMapper mapper = new ObjectMapper();
      response.setContentType("application/json");
      mapper.writeValue(response.getOutputStream(), cakes);
    } catch (SQLException e) {
      throw new ServletException("Unable to query cakes", e);
    }
  }

  @Override
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    try (Connection connection = dataSource.getConnection()) {
      List<Cake> cart = new ObjectMapper().readValue(request.getInputStream(),
          new TypeReference<List<Cake>>() {});
      for (Cake cake : cart) {
        PreparedStatement statement = connection.prepareStatement(
            "UPDATE cakes SET quantity = quantity - ? WHERE id = ?");
        statement.setInt(1, cake.getQuantity());
        statement.setInt(2, cake.getId());
        statement.executeUpdate();
      }
      ObjectMapper mapper = new ObjectMapper();
      response.setContentType("application/json");
      mapper.writeValue(response.getOutputStream(), cart);
    } catch (SQLException e) {
      throw new ServletException("Unable to buy cakes", e);
    }
  }
}

这里假设数据库中有一个名为cakes的表，包含id、name、price和quantity四个字段。在web.xml中配置数据源：

<resource-ref>
  <description>DB Connection</description>
  <res-ref-name>jdbc/cake</res-ref-name>
  <res-type>javax.sql.DataSource</res-type>
  <res-auth>Container</res-auth>
</resource-ref>

<resource-env-ref>
  <description>DB Connection Pool</description>
  <resource-env-ref-name>jdbc/cake</resource-env-ref-name>
  <resource-env-ref-type>javax.sql.DataSource</resource-env-ref-type>
</resource-env-ref>

<resource-env-ref>
  <description>DB Connection Properties</description>
  <resource-env-ref-name>jdbc/cake/properties</resource-env-ref-name>
  <resource-env-ref-type>java.util.Properties</resource-env-ref-type>
</resource-env-ref>

<resource-ref>
  <description>DB Connection Pool</description>
  <res-ref-name>jdbc/cake</res-ref-name>
  <res-type>javax.sql.DataSource</res-type>
  <res-auth>Container</res-auth>
  <mapped-name>java:comp/env/jdbc/cake</mapped-name>
  <lookup-name>jdbc/cake</lookup-name>
</resource-ref>

以上代码示例仅为参考，实际实现中需要根据具体需求进行修改。