【JDBC 】
文章目录
- JDBC
-
- 概念
- 四个核心的对象
- 使用步骤
-
-
- statement执行sql语句的时候会有sql注入的风险，所以推荐使用PreparedStatemen
- 查询使用executeQuery(); 增删改使用executeUpdate()；
- 实体类
- dao层代码
-
JDBC
概念
- Java Database Connectivity，简称JDBC
- JDBC：sun公司定义的一套操作数据库的规范，就是接口
四个核心的对象
- DriverManager：依据数据库的不同，管理JDBC驱动
- Connection： 负责连接数据库并担任传送数据的任务
- Statement： 由 Connection 产生、负责执行SQL语句
- ResultSet：负责保存Statement执行后所产生的查询结果
使用步骤
- 注册驱动
- 获取数据库连接对象 Connection
- 定义sql
- 获取执行sql语句的对象 Statement
- 执行sql，接受返回结果
- 处理结果
- 释放资源
#### 注册驱动
Class.forName("com.mysql.jdbc.Driver");
- 括号中的数据不知道怎么写的时候，可以去复制
#### 获取数据库连接对象 Connection，故名思意，连接肯定需要连接的地址，用户名和密码
Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/xinzhi666", "root", "root");
- 如果java操作数据库的时候有乱码，可以在地址后面跟 ?useUnicode=true&characterEncoding=UTF-8
#### 定义sql语句，就是个字符串，如果需要字符串拼接，注意单引号。
String sql = "update person set name='赵琳鹏' where id=1";
#### 获取执行sql语句的对象 Statement，是由连接对象创建出来的
Statement statement = connection.createStatement();
#### 执行sql，接受返回结果
- 1.查询executeQuery(SQL)，会有返回值ResultSet，保存了查询的结果
- 2.增删改executeUpdate(增删改SQL)，返回一个数据，表示数据库中受影响的行数
#### 处理结果
- ResultSet，可以把ResultSet看成我们java里的set,迭代的时候用next()方法
- 获取每一列resultSet.getString()，括号中的参数可以是数字，从1开始，表示第几列，也可以是字符串，列名的字符串。
#### 释放资源
调用close()的方法
```
## sql注入
statement执行sql语句的时候会有sql注入的风险，所以推荐使用PreparedStatemen
PreparedStatement ps = con.prepareStatement(sql);
sql语句中的参数可以使用?代替
statement.setInt(索引，值); 索引从1开始的
setXXX XXX代表数据类型
查询使用executeQuery(); 增删改使用executeUpdate()；
## 工具类
public class JDBCUtils {
private JDBCUtils(){}
private static String url = “jdbc:mysql://localhost:3306/xinzhi666?useUnicode=true&characterEncoding=UTF-8”;
private static String user=“root”;
private static String password=“root”;
private static String driver=“com.mysql.jdbc.Driver”;
static {
try {
Class.forName(driver);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public static Connection getConnection(){
Connection connection = null;
try {
connection = DriverManager.getConnection(url,user,password);
} catch (SQLException e) {
e.printStackTrace();
}
return connection;
}
public static void release(Connection connection, Statement statement, ResultSet resultSet){
if(resultSet!=null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(connection!=null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(statement!=null){
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
## 案列
### 创建jdbc项目，并且导入资料中的jar包
### 创建JDBC工具类
package utils;
import java.sql.*;
/**
-
工具类 ，也有人叫 BaseDao
*/
public class JDBCUtils {private JDBCUtils(){
}
public static Connection getConnection(){
Connection connection = null;
try {
Class.forName(“com.mysql.jdbc.Driver”);
connection = DriverManager.getConnection(“jdbc:mysql://localhost:3306/xinzhi666?useUnicode=true&characterEncoding=UTF-8”, “root”, “root”);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return connection;
}public static void release(ResultSet rs, Statement statement,Connection connection){
if(rs!=null){ try { rs.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if(statement!=null){ try { statement.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if(connection!=null){ try { connection.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } }}
public static void release( Statement statement,Connection connection){
if(statement!=null){ try { statement.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if(connection!=null){ try { connection.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } }}
}
### 加密工具
package utils;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
public class MD5Utils {
public static String encrypt(String password){
MessageDigest md = null;
String s = null;
try {
md = MessageDigest.getInstance("MD5");
md.update(password.getBytes());
s = new BigInteger(1, md.digest()).toString(16);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return s;
}
}
实体类
package model;
/**
* 实体类 ，一般放在model包下， entity
*/
public class User {
private int id;
private String username;
private String password;
private String name;
private String phone;
private String email;
public User() {
}
public User(int id, String username, String password, String name, String phone, String email) {
this.id = id;
this.username = username;
this.password = password;
this.name = name;
this.phone = phone;
this.email = email;
}
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 getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", password='" + password + '\'' +
", name='" + name + '\'' +
", phone='" + phone + '\'' +
", email='" + email + '\'' +
'}';
}
}
dao层代码
package dao;
import model.User;
public interface ILoginDao {
/**
* 注册
* @param user 用户的实体类
* @return 返回值是一个数字，表示数据库中受影响的行数
*/
int register(User user);
/**
* 登录
* @param username 用户名
* @param password 密码
* @return
*/
User login(String username, String password);
/**
* 修改用户信息
* @param user
* @return
*/
int update(User user,String pw);
/**
* 删除用户
* @param username
* @param password
* @return
*/
int delete(String username, String password);
}
package dao.impl;
import dao.ILoginDao;
import model.User;
import utils.JDBCUtils;
import utils.MD5Utils;
import java.sql.*;
public class LoginDaoImpl implements ILoginDao {
@Override
public int register(User user) {
Connection connection = null;
PreparedStatement statement = null;
int i = 0;
try {
connection = JDBCUtils.getConnection();
String sql = "insert into user () values (?,?,?,?,?,?)";
statement = connection.prepareStatement(sql);
statement.setInt(1,user.getId());
statement.setString(2,user.getUsername());
statement.setString(3, MD5Utils.encrypt(user.getPassword()));
statement.setString(4,user.getName());
statement.setString(5,user.getPhone());
statement.setString(6,user.getEmail());
i = statement.executeUpdate(); // 数据库中受影响的行数
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
//7 释放资源
JDBCUtils.release(statement,connection);
}
return i;
}
@Override
public User login(String username, String password) {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
String sql = "select id,username,password,name,phone,email from user where username=? and password=?";
try {
connection = JDBCUtils.getConnection();
statement = connection.prepareStatement(sql);
statement.setString(1,username);
statement.setString(2,MD5Utils.encrypt(password));
resultSet = statement.executeQuery();
while (resultSet.next()){
User user = new User();
String id = resultSet.getString("id");
user.setId(Integer.parseInt(id));
user.setUsername(resultSet.getString("username"));
user.setPassword(resultSet.getString("password"));
user.setName(resultSet.getString("name"));
user.setPhone(resultSet.getString("phone"));
user.setEmail(resultSet.getString("email"));
return user;
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCUtils.release(resultSet,statement,connection);
}
return null;
}
@Override
public int update(User user,String pw) {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
String sql = "update user set name=?,phone=?,password=? where username=? and password=?";
try {
connection = JDBCUtils.getConnection();
statement = connection.prepareStatement(sql);
statement.setString(1,user.getName());
statement.setString(2,user.getPhone());
statement.setString(3,MD5Utils.encrypt(pw));
statement.setString(4,user.getUsername());
statement.setString(5,MD5Utils.encrypt(user.getPassword()));
int i = statement.executeUpdate();
return i;
}catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCUtils.release(resultSet,statement,connection);
}
return 0;
}
@Override
public int delete(String username, String password) {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
String sql = "delete from user where username=? and password=?";
try {
connection = JDBCUtils.getConnection();
statement = connection.prepareStatement(sql);
statement.setString(1,username);
statement.setString(2,password);
int i = statement.executeUpdate();
return i;
}catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCUtils.release(resultSet,statement,connection);
}
return 0;
}
}
### 测试
import dao.impl.LoginDaoImpl;
import model.User;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Scanner;
public class Test01 {
public static void main(String[] args) {
LoginDaoImpl loginDao = new LoginDaoImpl();
// int num = loginDao.register(new User(6, “qinyuzhao”, “123456”, “老韩”, “13111223344”, “[email protected]”));
// if(num>0){
// System.out.println(“注册成功”);
// }else {
// System.out.println(“注册失败”);
// }
// User user = loginDao.login(“qinyuzhao”, “123456”);
// if(user!=null){
// System.out.println(“登录成功，欢迎”+user.getName()+“回来”);
// }else {
// System.out.println(“登录失败”);
// }
// int update = loginDao.update(new User(6, “qinyuzhao”, “123456”, “秦昱照”, “12315”, “[email protected]”),“root”);
// if(update>0){
// System.out.println(“修改成功”);
// }else {
// System.out.println(“修改失败”);
// }
// int delete = loginDao.delete(“changkaixun”, “zhanan”);
// if(delete>0){
// System.out.println(“删除成功”);
// }else {
// System.out.println(“删除失败”);
// }
// Test01 test01 = new Test01();
// Scanner scanner = new Scanner(System.in);
// System.out.println(“请输入要加密的字符串：”);
// String str = scanner.next();
// String encrypt = test01.encrypt(str);
// System.out.println(“加密前：”+str+“,加密后的：”+encrypt);
}
public String encrypt(String password){
MessageDigest md = null;
String s = null;
try {
md = MessageDigest.getInstance("MD5");
md.update(password.getBytes());
s = new BigInteger(1, md.digest()).toString(16);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return s;
}
}