本項(xiàng)目是一個(gè)基于JSP和MySQL的購物車網(wǎng)站。主要功能包括瀏覽商品、加入購物車、結(jié)算等。以下是部分代碼實(shí)現(xiàn)：

<%@ page import="java.sql.*"%>
<%@ page import="java.util.*"%>
<%
String product_id = request.getParameter("product_id");
String quantity = request.getParameter("quantity");
ResultSet rs = null;
Statement st = null;
Connection con = null;
if (session.getAttribute("cart") == null) {
Map<String, Integer> cart = new HashMap<String, Integer>();
cart.put(product_id, Integer.parseInt(quantity));
session.setAttribute("cart", cart);
} else {
Map<String, Integer> cart = (Map<String, Integer>) session.getAttribute("cart");
if (cart.containsKey(product_id)) {
cart.put(product_id, cart.get(product_id) + Integer.parseInt(quantity));
} else {
cart.put(product_id, Integer.parseInt(quantity));
}
session.setAttribute("cart", cart);
}
%>

以上代碼實(shí)現(xiàn)加入購物車的功能。通過傳遞商品ID和數(shù)量，將對應(yīng)的購物車數(shù)據(jù)存儲在session中。下面是結(jié)算頁面的數(shù)據(jù)庫查詢實(shí)現(xiàn)：

<table>
<% 
double totalPrice = 0.0;
if (session.getAttribute("cart") != null) {
Map<String, Integer> cart = (Map<String, Integer>) session.getAttribute("cart");
Set<String> ids = cart.keySet();
if (ids.size() >0) {
String sql ="SELECT * FROM products WHERE product_id IN (";
for (String id : ids) {
sql += id + ",";
}
sql = sql.substring(0, sql.length() - 1) + ")";
try {
con = DriverManager.getConnection(url, user, password);
st = con.createStatement();
rs = st.executeQuery(sql);
while (rs.next()) {
int quantity = cart.get(rs.getString("product_id"));
double price = rs.getDouble("price");
out.println("<tr>");
out.println("<td>" + rs.getString("product_name") + "</td>");
out.println("<td>" + quantity + "</td>");
out.println("<td>$" + price + "</td>");
double total = quantity * price;
totalPrice += total;
out.println("<td>$" + total + "</td>");
out.println("</tr>");
}
} catch (SQLException e) {
out.println("Error: " + e.getMessage());
} finally {
try {
if (rs != null) {
rs.close();
}
if (st != null) {
st.close();
}
if (con != null) {
con.close();
}
} catch (SQLException e) {
out.println("Error: " + e.getMessage());
}
}
}
}
%>
<tr>
<td colspan="3"></td>
<td><b>Total: $<%= totalPrice %></b></td>
</tr>
</table>

以上代碼通過查詢購物車中的商品ID對應(yīng)的產(chǎn)品信息，計(jì)算購物車中所有商品的總價(jià)，最后輸出到頁面中。同時(shí)，需要注意數(shù)據(jù)庫連接的釋放操作，以免出現(xiàn)資源泄露。