6 JDBC

JDBC

理解图

需要mysql包

下载官网：https://downloads.mysql.com/archives/c-j/

第一个JDBC项目

1. 创建一个java项目,一路next

2. 导入jar包

   1. 
   2. 

如果是Maven项目的话，在pom.xml文件输入

 <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
</dependency>

3. 编写测试代码

   步骤：

   1. 加载驱动 ——打开SQLyog
   2. 用户信息和url——输入用户账号密码和url (localhost)
   3. 连接成功，数据库对象——点击连接
   4. 获得执行SQL的对象
   5. 获得返回结果集合——执行语句，返回结果
   6. 释放连接

   import java.sql.*;
   public class jdbc_01 {
       public static void main(String[] args) throws ClassNotFoundException, SQLException {
           //1. 加载驱动 ——打开SQLyog
           Class.forName("com.mysql.jdbc.Driver");//固定写法
           //2. 用户信息和url
           //useUnicode=true 支持中文编码 &characterEncoding=utf8 设置中文字符UTF8&useSSL=true 使用安全的连接
           String url = "jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&characterEncoding=utf8&useSSL=true";
           String username="root";
           String password="123456";
           //3. 连接成功，数据库对象
           Connection connection = DriverManager.getConnection(url, username, password);
           //4. 获得执行SQL的对象
           Statement statement = connection.createStatement();
           //5. 获得返回结果集合
           String sql = "SELECT * FROM users";
           ResultSet resultSet = statement.executeQuery(sql);
   
           while(resultSet.next()){
               System.out.println(resultSet.getObject("id"));
               System.out.println(resultSet.getObject("name"));
           }
           //6.释放连接
           resultSet.close();
           statement.close();
           connection.close();
       }
   }
   

DriverManager

//加载驱动，不返回对象的原因（即不new的原因）
Class.forName("com.mysql.jdbc.Driver");
//com.mysql.jdbc.Driver类中存在了DriverManager.registerDriver(new Driver());

URL

String url = "jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&characterEncoding=utf8&useSSL=true";
//mysql 默认3306端口
//jdbc:mysql 理解成https 就是连接Mysql 
//localhost  理解成www.baidu.com
//jdbcStudy 数据库名

Connection

Connection connection = DriverManager.getConnection(url, username, password);
//connection 代表数据库
//数据库设置自动提交connection.getAutoCommit();
//事务提交connection.commit();
//事务回滚connection.rollback();

statement 执行SQL 的对象 prepareStatement

statement用于向是数据库发送sql

statement.executeQuery();//查询 返回ResultSet
statement.executeUpdate();//更新 插入 删除 返回受影响的行数
statement.execute();//SQL语句

Resultset 查询的结果集

resultSet.getString();
resultSet.getFloat();
resultSet.getInt();
resultSet.getObject();//知道类的类型就使用指定类型

resultSet.next();

释放资源 不关耗资源

resultSet.close();
statement.close();
connection.close();

封装

1. 编写配置

2. 编写工具类

3. 编写测试类

文件结构

db.properties(字符串不用加引号)

driver = com.mysql.jdbc.Driver
url = jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&characterEncoding=utf8&useSSL=true
username = root
password = 123456

工具类

package cn.dj.www.lesson01;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

public class JdbcUtil {
    private static String driver=null;
    private static String url=null;
    private static String username=null;
    private static String password=null;

    static{
        try{
            //./ 表示上一级目录
            InputStream inputStream = JdbcUtil.class.getClassLoader().getResourceAsStream("db.properties");
            Properties properties = new Properties();
            properties.load(inputStream);
            driver=properties.getProperty("driver");
            url=properties.getProperty("url");
            username=properties.getProperty("username");
            password=properties.getProperty("password");

            //驱动只要加载一次
            Class.forName(driver);

        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    //获取连接
    public static Connection getConnection() throws SQLException {
        return  DriverManager.getConnection(url, username, password);
    }
    //释放连接
    public static void release(Connection connection, Statement statement, ResultSet resultSet)  {
        if(resultSet!=null){
            try {
                resultSet.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();
            }
        }
    }
}

测试类

package cn.dj.www.lesson01;

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

public class Test {
    public static void main(String[] args) throws SQLException {
        Connection connection = JdbcUtil.getConnection();
        Statement statement = connection.createStatement();
        String name = "li%";//注意有''
        String sql = "SELECT * FROM users " +
                "where name like '"+name+"'";

        ResultSet rs = statement.executeQuery(sql);
        while(rs.next()){
            System.out.println(rs.getString("name"));
            System.out.println(rs.getInt("id"));
        }
        JdbcUtil.release(connection,statement,rs);

    }

}

statement对象导致SQL注入

典型例子

String id = "1 or 1=1";
String sql = "SELECT * FROM users " +"where id = "+id;

prepareStatement

更安全，效率更高

package cn.dj.www.lesson01;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Date;

public class PTest {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement pst =null;
        try {
            conn  = JdbcUtil.getConnection();
            String sql = "insert into users(id,`name`,`password`,`email`,`birthday`)"+
                   "values(?,?,?,?,?)";
            pst = conn.prepareStatement(sql);//预编译
            //传递参数
            pst.setInt(1,4);
            pst.setString(2,"DJ");
            pst.setString(3,"123456");
            pst.setString(4,"123@163.com");
            // java Date().getTime() 获得时间戳
            pst.setDate(5, new java.sql.Date(new Date().getTime()));

            int i = pst.executeUpdate();
            if(i>0){
                System.out.println("插入成功！");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JdbcUtil.release(conn,pst,null);
        }

    }
}

解决1=1注入的例子

//防止SQL注入的本质：把传递进来的参数当做字符就是外面再包了'',假设其中存在转移字符如（‘）就直接忽略了
String name =" '' or 1=1";
String sql = "SELECT * FROM users " +"where name = ?";
pst.setString(1,name);