JDBC初体验（二）
一、SQL注入
1.1 SQL注入原理
利用现有应用程序，将（恶意的）SQL命令注入到后台数据库引擎执行的能力，它可以通过在web表单中输入（恶意的）SQL语句得到一个存在安全漏洞的网站上的数据库，而不是按照设计者意图去执行SQL语句
1.2 防止SQL注入的方法
- 过滤用户输入的数据中是否包含非法字符
- 分步校验，先使用用户名来查询用户，如果查到了，再比较密码
- 使用PreparedStatement接口
二、PreparedStatement接口
PreparedStatement接口是Statement的子接口，可以使用该接口来替换Statement接口
PreparedStatement的使用
- 使用Connection对象的preparedStatement(String sql):即创建它时就让它与一条SQL语句绑定
- 编写SQL语句时，如果存在参数，就是用？作为数据占位符
- 调用PreparedStatement的setXXX()系列方法为占位符设置值，索引从1开始
- 调用executeUpdated()或executeQuery()方法，但要注意，要调用没有参数的方法
三、增、删、改、查操作代码演示
3.1 User类
package day02.pojo;
/**
* @desc:User类
*/
public class User {
private int id;
private String userName;
private String userPass;
private int role;
public User(int id, String userName, String userPass, int role) {
this.id = id;
this.userName = userName;
this.userPass = userPass;
this.role = role;
}
public User() {
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getUserPass() {
return userPass;
}
public void setUserPass(String userPass) {
this.userPass = userPass;
}
public int getRole() {
return role;
}
public void setRole(int role) {
this.role = role;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", userName='" + userName + '\'' +
", userPass='" + userPass + '\'' +
", role=" + role +
'}';
}
}3.2 JDBC/增删改查类
package day02.IncreaseDeleteChangeQuery;
import day02.pojo.User;
import java.sql.*;
/**
* @desc:JDBC类、增删改查类
*/
public class UserDao {
Connection connection =null;
Statement statement =null;
PreparedStatement ps = null;
ResultSet resultSet =null;
/**
* 用户登录
* @param userName 用户名
* @param userPass 用户密码
* @return User
*/
public User toLogin(String userName,String userPass){
//1.获取连接对象
getConnection();
//2.编写SQL语句
String sql = "select ID,USERNAME,ROLE from user where userName = ? and userPass = ?";
System.out.println("要执行的SQL语句是：" + sql);
//3.创建statement对象
User user = null;
try {
// 创建PreparedStatement对象 发送SQL语句并预执行
ps = connection.prepareStatement(sql);
//3.1处理参数
ps.setString(1,userName);
ps.setString(2,userPass);
//4.执行并解析结果
resultSet = ps.executeQuery();
while (resultSet.next()){
user = new User();
user.setId(resultSet.getInt(1));
user.setUserName(resultSet.getString(2));
user.setRole(resultSet.getInt(3));
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
closeResource();
}
return user;
}
/**
* 增删改查——查
*/
public User login(String userName,String userPass){
//1.获取连接对象
getConnection();
//2.编写SQL语句
String sql = "select ID,USERNAME,ROLE from user where userName = '"+userName+"' and userPass = '"+userPass+"'";
System.out.println("要执行的SQL语句是：" + sql);
//3.创建statement对象
User user = null;
try {
statement = connection.createStatement();
resultSet = statement.executeQuery(sql);
//4.解析结果
while (resultSet.next()){
user = new User();
user.setId(resultSet.getInt(1));
user.setUserName(resultSet.getString(2));
user.setRole(resultSet.getInt(3));
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
closeResource();
}
return user;
}
public User login2(String userName,String userPass){
//1.获取连接对象
getConnection();
//2.编写SQL语句
String sql = "select ID,USERNAME,USERPASS,ROLE from user where userName = '"+userName+"'";
System.out.println("要执行的SQL语句是：" + sql);
//3.创建statement对象
User user = null;
try {
statement = connection.createStatement();
resultSet = statement.executeQuery(sql);
//4.解析结果
while (resultSet.next()){
user = new User();
user.setId(resultSet.getInt(1));
user.setUserName(resultSet.getString(2));
user.setUserPass(resultSet.getString(3));
user.setRole(resultSet.getInt(4));
}
if(userPass.equals(user.getUserPass())){
return user;
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
closeResource();
}
return null;
}
/**
* 增删改查——增
*/
public int saveUser(User user) {
int line = 0;
//1、获取连接对象
getConnection();
//2、编写SQL语句
String sql = "insert into user values(default,?,?,?)";
try {
ps = connection.prepareStatement(sql);
ps.setString(1, user.getUserName());
ps.setString(2,user.getUserPass());
ps.setInt(3,user.getRole());
//3、执行 增删改的执行方法是excuteUpdate()
//返回一个整数，表示受影响的行数
line = ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
closeResource();
}
return line;
}
/**
* 增删改查——改
*/
public int updateUser(User user) {
int line = 0;
//1、获取连接对象
getConnection();
//2、编写SQL语句
String sql = "update user set USERNAME=?,USERPASS=?,ROLE=? where ID=?";
try {
ps = connection.prepareStatement(sql);
ps.setString(1, user.getUserName());
ps.setString(2,user.getUserPass());
ps.setInt(3,user.getRole());
ps.setInt(4,user.getId());
//3、执行 增删改的执行方法是excuteUpdate()
//返回一个整数，表示受影响的行数
line = ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
closeResource();
}
return line;
}
/**
* 增删改查——删
*/
public int deleteUser(int id) {
int line = 0;
//1、获取连接对象
getConnection();
//2、编写SQL语句
String sql = "delete from user where id = ?";
try {
ps = connection.prepareStatement(sql);
ps.setInt(1,id);
//3、执行 增删改的执行方法是excuteUpdate()
//返回一个整数，表示受影响的行数
line = ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
closeResource();
}
return line;
}
//↓↓↓以下两部分代码是固定的，不需要改动，所以封装起来
/**
* 加载驱动和建立连接
*/
public Connection getConnection(){
try {
//1.加载驱动
Class.forName("com.mysql.jdbc.Driver");
//2.建立连接
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/myschool?useSSL=false","root","zkz2002513>");
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return connection;
}
/**
* 关闭资源
*/
public void closeResource(){
if(resultSet!=null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(ps!=null){
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(statement!=null){
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(connection!=null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}3.3 增删改查——增
package day02.IncreaseDeleteChangeQuery;
import day02.pojo.User;
/**
* @desc:增删改查操作——增加main方法
*/
public class IncreaseMain {
public static void main(String[] args) {
UserDao userDao = new UserDao();
User user = new User();
user.setUserName("诸葛亮");
user.setUserPass("9087666");
user.setRole(3);
int line = userDao.saveUser(user);
System.out.println(line > 0 ? "添加成功": "添加失败");
}
}3.4 增删改查——删
package day02.IncreaseDeleteChangeQuery;
/**
* @desc:增删改查操作——删除main方法
*/
public class DeleteMain {
public static void main(String[] args) {
UserDao userDao = new UserDao();
int line = userDao.deleteUser(11);
System.out.println(line > 0 ? "删除成功": "删除失败");
}
}3.5 增删改查——改
package day02.IncreaseDeleteChangeQuery;
import day02.pojo.User;
import java.util.Scanner;
/**
* @desc:增删改查操作——改main方法
*/
public class ChangeMain {
public static void main(String[] args) {
/* Scanner sc = new Scanner(System.in);
System.out.println("请输入要修改的用户id：");
int id = sc.nextInt();
System.out.println("请输入要修改的用户名：");
String username = sc.next();
System.out.println("请输入新的的密码：");
String password = sc.next();
System.out.println("请输入角色类型：");
int role = sc.nextInt();
User user = new User(id, username, password, role);
UserDao userDao = new UserDao();*/
UserDao userDao = new UserDao();
User user = new User(8,"赵云","24678",2);
int line = userDao.updateUser(user);
System.out.println(line > 0 ? "修改成功" : "修改失败");
}
}3.6 增删改查——查
package day02.IncreaseDeleteChangeQuery;
import day02.pojo.User;
import java.util.Scanner;
/**
* @desc:增删改查操作——查询main方法
*/
public class QueryMain {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
UserDao userDao = new UserDao();
System.out.println("****************************************");
System.out.println("\t\t\t\t\t用户管理系统");
System.out.println("****************************************");
System.out.print("请输入用户名：");
String userName = sc.next();
System.out.print("请输入密码：");
String userPass = sc.next();
User user = userDao.toLogin(userName,userPass);
if (user == null) {
System.out.println("登录失败，用户名或密码错误！");
} else {
System.out.println("登录成功，欢迎【" + user.getUserName() + "】！");
}
}
}