13. JDBC

JDBC

import java.sql.*;
public class JdbcFirstDemo {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        // 1. 加载驱动
        Class.forName("com.mysql.jdbc.Driver"); // 固定写法 加载驱动 内部源码就是一个静态代码块
                                                // 执行就行
        // 2. url 账号密码
        String url = "jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf8&useSSL=false";
        String username = "root";
        String password = "123456";
        // 3. 连接成功，数据库对象
        Connection connection = DriverManager.getConnection(url, username, password);
        // 4. 执行sql语句的对象
        Statement statement = connection.createStatement();
        //5. 执行sql
        String sql = "SELECT * FROM user";
        ResultSet resultSet = statement.executeQuery(sql);
        while(resultSet.next()){
            System.out.println("id: "+resultSet.getObject("id"));
            System.out.println("name: "+resultSet.getObject("name"));
            System.out.println("pwd: "+resultSet.getObject("pwd"));
            System.out.println("===================");
        }
        //6. 释放对象
        resultSet.close();
        statement.close();
        connection.close(); // 消耗资源，用完关掉
    }
}

id: 1
name: 张三
pwd: 123456
===================
id: 2
name: 李四
pwd: 122222
===================
id: 3
name: 王超
pwd: 133333
===================
id: 4
name: 马汉
pwd: 144444
===================
Process finished with exit code 0

url

String url = "jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf8&useSSL=false";
//jdbc:mysql://主机：端口/数据库名？参数1&参数2&参数3

// 3. 连接成功，数据库对象
Connection connection = DriverManager.getConnection(url, username, password);
// connection代表数据库 事务提交  事务回滚

// 4. 执行sql语句的对象
Statement statement = connection.createStatement();
//Statement 具体执行类  执行增删改查语句
statement.executeQuery(); //查询操作 返回结果集
statement.execute(); //执行任何sql
statement.executeUpdate(); //更新 插入 删除 返回受影响的行数

//5. 执行sql
String sql = "SELECT * FROM user";
ResultSet resultSet = statement.executeQuery(sql);
while(resultSet.next()){
    System.out.println("id: "+resultSet.getObject("id"));
    System.out.println("name: "+resultSet.getObject("name"));
    System.out.println("pwd: "+resultSet.getObject("pwd"));
    System.out.println("===================");
}
resultset.getString(); // 知道具体类型 就用get+类型 不知道用object
resultset.getInt();

Statement对象

statement对象用于向数据库发送SQL命令。
提取工具类

package com.angyi.utils;
import javax.swing.plaf.nimbus.State;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;
public class JdbcUtils {
    private static String url=null;
    private static String driver=null;
    private static String pwd=null;
    private static String username=null;
    static{
        InputStream inputStream = ClassLoader.getSystemResourceAsStream("db.properties");
        Properties properties = new Properties();
        try {
            properties.load(inputStream);
            url = properties.getProperty("jdbc.url");
            driver = properties.getProperty("jdbc.driver");
            pwd = properties.getProperty("jdbc.password");
            username = properties.getProperty("jdbc.username");
            //1。 驱动只需要加载一次
            Class.forName(driver);
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    public static Connection getConnection() throws ClassNotFoundException, SQLException {
        Connection connection = DriverManager.getConnection(url,username,pwd);
        return connection;
    }
    public static void release(Connection con, Statement st,ResultSet rs) throws SQLException {
        if(con!=null){
            try{
                con.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
        if(st!=null){
            try{
                con.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
        if(rs!=null){
            try{
                con.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
    }
}