/*
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 * and open the template in the editor.
 */

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

/**
 *
 * @author Administrator
 */
@WebServlet(name = "testServlet",
        urlPatterns = {"/testServlet"},
        initParams = {
            @WebInitParam(name = "driver", value = "com.mysql.cj.jdbc.Driver")
            ,
        @WebInitParam(name = "url", value = "jdbc:mysql://localhost:3306/taobao")
            ,
        @WebInitParam(name = "user", value = "root")
            ,
        @WebInitParam(name = "pass", value = "admin")})
public class TestServlet extends HttpServlet {
        // 重写init方法
    public void init(ServletConfig config) throws ServletException {
        // 重写该方法，应该首先调用父类的init()方法
        super.init(config);
    }
    // 响应客户端请求的方法
    public void service(HttpServletRequest request,HttpServletResponse response)
            throws ServletException, java.io.IOException {
        try {
            // 获取ServletConfig对象
            ServletConfig config = getServletConfig();
            // 通过ServletConfig对象获取配置参数：dirver
            String driver = config.getInitParameter("driver");
            // 通过ServletConfig对象获取配置参数：url
            String url = config.getInitParameter("url");
            // 通过ServletConfig对象获取配置参数：user
            String user = config.getInitParameter("user");
            // 通过ServletConfig对象获取配置参数：pass
            String pass = config.getInitParameter("pass");
            // 注册驱动
            Class.forName(driver);
            // 获取数据库连接
            Connection conn = DriverManager.getConnection(url, user, pass);
            // 创建Statement对象
            Statement stmt = conn.createStatement();
            // 执行查询，获取ResuletSet对象
            ResultSet rs = stmt.executeQuery("select * from person");
            response.setContentType("text/html;charSet=UTF-8");
            // 获取页面输出流
            PrintStream out = new PrintStream(response.getOutputStream());
            // 输出HTML标签
            out.println("<html>");
            out.println("<head>");
            out.println("<title>访问Servlet初始化参数测试</title>");
            out.println("</head>");
            out.println("<body>");
            out.println("<table bgcolor=\"#9999dd\" border=\"1\""
                    + "width=\"480\">");
            // 遍历结果集
            while (rs.next()) {
                // 输出结果集内容
                out.println("<tr>");
                out.println("<td>" + rs.getInt(1) + "</td>");
                out.println("<td>" + rs.getString(2) + "</td>");
                out.println("<td>" + rs.getInt(3) + "</td>");
                out.println("</tr>");
            }
            out.println("</table>");
            out.println("</body>");
            out.println("</html>");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
<?xml version="1.0" encoding="UTF-8"?>
<web-app metadata-complete="true" version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee                       http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
    <!-- 配置Servlet的名字 -->
    <servlet>
        <!-- 指定Servlet的名字，
        相当于指定@WebServlet的name属性 -->
        <servlet-name>firstServlet</servlet-name>
        <!-- 指定Servlet的实现类 -->
        <servlet-class>FirstServlet</servlet-class>
    </servlet>
    <!-- 配置Servlet的URL -->
    <servlet-mapping>
        <!-- 指定Servlet的名字 -->
        <servlet-name>firstServlet</servlet-name>
        <!-- 指定Servlet映射的URL地址，
        相当于指定@WebServlet的urlPatterns属性-->
        <url-pattern>/aa</url-pattern>
    </servlet-mapping>
    <servlet>
        <!-- Servlet名 -->
        <servlet-name>timerServlet</servlet-name>
        <!-- Servlet的实现类 -->
        <servlet-class>TimerServlet</servlet-class>
        <!-- 配置应用启动时，创建Servlet实例
        ，相当于指定@WebServlet的loadOnStartup属性-->
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet>
        <!-- 配置Servlet名 -->
        <servlet-name>testServlet</servlet-name>
        <!-- 指定Servlet的实现类 -->
        <servlet-class>TestServlet</servlet-class>
        <!-- 配置Servlet的初始化参数：driver -->
        <init-param>
            <param-name>driver</param-name>
            <param-value>com.mysql.cj.jdbc.Driver</param-value>
        </init-param>
        <!-- 配置Servlet的初始化参数：url -->
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/taobao</param-value>
        </init-param>
        <!-- 配置Servlet的初始化参数：user -->
        <init-param>
            <param-name>user</param-name>
            <param-value>root</param-value>
        </init-param>
        <!-- 配置Servlet的初始化参数：pass -->
        <init-param>
            <param-name>pass</param-name>
            <param-value>admin</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <!-- 确定Servlet名 -->
        <servlet-name>testServlet</servlet-name>
        <!-- 配置Servlet映射的URL -->
        <url-pattern>/testServlet</url-pattern>
    </servlet-mapping>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>