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掌握Servlet与数据库交互：实战案例分析全解析

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引言

Servlet是Java EE技术中用于处理HTTP请求和响应的核心组件之一。在Web应用开发中，Servlet与数据库的交互是必不可少的。本文将通过对一个实战案例的分析，详细解析Servlet与数据库交互的过程，帮助读者更好地理解和掌握这一技术。

案例背景

假设我们正在开发一个简单的在线书店系统，其中包含书籍信息、用户信息和订单信息等数据。为了实现系统功能，我们需要使用Servlet与数据库进行交互。

1. 数据库设计

首先，我们需要设计数据库表结构。以下是一个简单的示例：

CREATE TABLE books (
    id INT PRIMARY KEY AUTO_INCREMENT,
    title VARCHAR(100),
    author VARCHAR(100),
    price DECIMAL(10, 2)
);

CREATE TABLE users (
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(50),
    password VARCHAR(50)
);

CREATE TABLE orders (
    id INT PRIMARY KEY AUTO_INCREMENT,
    user_id INT,
    book_id INT,
    quantity INT,
    order_date DATE,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (book_id) REFERENCES books(id)
);

2. Servlet开发

接下来，我们将开发一个Servlet来处理用户请求。以下是一个简单的示例：

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class BookServlet extends HttpServlet {
    private Connection conn;

    public void init() throws ServletException {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/bookstore", "root", "password");
        } catch (Exception e) {
            throw new ServletException("Error initializing database connection", e);
        }
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String action = request.getParameter("action");
        if ("listBooks".equals(action)) {
            listBooks(request, response);
        } else if ("addBook".equals(action)) {
            addBook(request, response);
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    private void listBooks(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        try {
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM books");
            out.println("<html><body>");
            out.println("<table border='1'><tr><th>ID</th><th>Title</th><th>Author</th><th>Price</th></tr>");
            while (rs.next()) {
                out.println("<tr><td>" + rs.getInt("id") + "</td><td>" + rs.getString("title") + "</td>"
                        + "<td>" + rs.getString("author") + "</td><td>" + rs.getDouble("price") + "</td></tr>");
            }
            out.println("</table></body></html>");
        } catch (SQLException e) {
            throw new ServletException("Error listing books", e);
        }
    }

    private void addBook(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String title = request.getParameter("title");
        String author = request.getParameter("author");
        double price = Double.parseDouble(request.getParameter("price"));
        try {
            PreparedStatement stmt = conn.prepareStatement("INSERT INTO books (title, author, price) VALUES (?, ?, ?)");
            stmt.setString(1, title);
            stmt.setString(2, author);
            stmt.setDouble(3, price);
            stmt.executeUpdate();
            response.sendRedirect("listBooks");
        } catch (SQLException e) {
            throw new ServletException("Error adding book", e);
        }
    }

    public void destroy() {
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

3. 配置web.xml

在web.xml文件中，我们需要配置Servlet映射：

<servlet>
    <servlet-name>BookServlet</servlet-name>
    <servlet-class>com.example.BookServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>BookServlet</servlet-name>
    <url-pattern>/books</url-pattern>
</servlet-mapping>

4. 测试

启动Tomcat服务器，访问http://localhost:8080/your-app-context/books?action=listBooks，即可看到书籍列表。访问http://localhost:8080/your-app-context/books?action=addBook，可以添加新书。

总结

本文通过一个实战案例，详细解析了Servlet与数据库交互的过程。通过学习本文，读者应该能够掌握如何使用Servlet与数据库进行交互，并能够将其应用到实际项目中。

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