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{
        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();
        }
    }
}