JDBC连接数据库（Servlet+JSP）

　　JDBC（Java Database connectivity）,是连接数据库的一种方式。后面的框架Mybatis和Hibernate等都封装的是JDBC。在JDBC中常用的API有4个：DriverManager、Connection、Statement、ResultSet。

代码演示：

　　首先要导入jar包: jstl_el、jstl-1.2_1、mysql-5.1.10

User.java

 public class User {
     private int id;
     private String age;
     private String name;

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getAge() {
         return age;
     }

     public void setAge(String age) {
         this.age = age;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }
 }

QueryServlet.java

 package cn.woo.servlet;

 import java.io.IOException;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.List;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import cn.woo.entity.User;
 import cn.woo.util.DBUtil;

 /**
  * 类说明：接收请求的Servlet
  *
  * @author wyh
  * @version 创建时间：2018年8月23日 下午2:46:29
  */
 public class QueryServlet extends HttpServlet {

     /**
      *
      */
     private static final long serialVersionUID = 1L;

     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         doPost(req, resp);
     }

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         req.setCharacterEncoding("utf-8");
         resp.setCharacterEncoding("utf-8");

         String action = req.getParameter("action");
         List<User> userList = new ArrayList<>();

         switch (action) {
         case "getUserList":
             try {
                 ResultSet resultSet = DBUtil.query("select * from user");
                 // 遍历结果集【一行行数据读取】，将结果集放置到实体对象中
                 while (resultSet.next()) {
                     User user = new User();
                     user.setId(resultSet.getInt("id"));
                     user.setAge(String.valueOf(resultSet.getInt("age")));
                     user.setName(resultSet.getString("name"));
                     userList.add(user);
                 }
                 req.setAttribute("userList",userList);
                 // 跳转至展示页面
                 req.getRequestDispatcher("../UserList.jsp").forward(req, resp);
             } catch (SQLException e) {
                 e.printStackTrace();
             }finally {
                 // 释放资源
                 DBUtil.closeResource();
             }
             break;
         case "deleteUserInfo":
             try {
                 String id = req.getParameter("id");
                 int delResult = DBUtil.insertOrDeleteOrUpdate("delete from user where id='"+id+"'");
                 if(delResult>0) {
                     System.out.println("删除成功");
                 }
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             break;
         case "updateUserName":
             try {
                 String id = req.getParameter("id");
                 String name = req.getParameter("name");
                 int updateResult = DBUtil.insertOrDeleteOrUpdate("update user set name='"+name+"' where id='"+id+"'");
                 if(updateResult>0) {
                     System.out.println("更新用户名成功");
                 }
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             break;
         case "insertUserInfo":
             try {
                 String addAge = req.getParameter("age");
                 String addName = req.getParameter("name");
                 int addResult = DBUtil.insertOrDeleteOrUpdate("insert into user(age,name) value('"+addAge+"','"+addName+"')");
                 if(addResult>0) {
                     System.out.println("新增用户成功");
                 }
             } catch (SQLException e) {
                 e.printStackTrace();
             }
             break;
         default:
             break;
         }
     }
 }

UserList.jsp

 <%@ page language="java" contentType="text/html; charset=UTF-8"
     pageEncoding="UTF-8"%>
 <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>用户信息列表</title>
 <style type="text/css">
     *{
         padding: 0;
         margin: 0;
     }

     table{
         margin: 300px auto;
     }

     td{
         width:100px;
         text-align: center;
     }
 </style>
 </head>
 <body>
     <table border="1" cellpadding="0" cellspacing="0">
         <tr>
             <td>序号</td>
             <td>工号</td>
             <td>年龄</td>
             <td>姓名</td>
         </tr>
         <c:forEach items="${ userList }" var="user" varStatus="status">
             <tr>
                 <td>${ status.index+1 }</td>
                 <td>${ user.id }</td>
                 <td>${ user.age }</td>
                 <td>${ user.name }</td>
             </tr>
         </c:forEach>
     </table>
 </body>
 </html>

DBUtil.java

 package cn.woo.util;

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;

 /**
 * 类说明：数据库连接工具类
 * @author wyh
 * @version 创建时间：2018年8月23日 下午3:58:55
 */
 public class DBUtil {

     private static Connection connection;
     private static Statement statement;

     static {
         try {
             DriverManager.registerDriver(new com.mysql.jdbc.Driver());
             // 获取连接 【并设置编码方式】
             connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/woo?unicode=true&characterEncoding=UTF-8","root","root");
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }

     public static Statement getStatement() throws SQLException {
         // 获取statement 【用于执行SQL语句】
         statement = connection.createStatement();
         return statement;
     }

     /**
      * 查
      * @param sql 执行查询的sql语句
       * @return resultSet 返回的结果集
      * @throws SQLException
      */
     public static ResultSet query(String sql) throws SQLException {
         return getStatement().executeQuery(sql);
     }

     /**
      * 增/删/改 通用方法
      * @param sql 要执行的SQL语句
       * @return 执行结果 >0表明执行成功
      * @throws SQLException
      */
     public static int insertOrDeleteOrUpdate(String sql) throws SQLException {
         return getStatement().executeUpdate(sql);
     }

     /**
      * 释放资源
      */
     public static void closeResource() {
         try {
             if(statement!=null) {
                 statement.close();
             }
             if(connection!=null) {
                 connection.close();
             }
         }catch(Exception e) {
             e.printStackTrace();
         }
     }
 }