JDBC基础（补）：相关配置文件，和工具类

db.properties(链接数据库配置文件)

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/jdbcstudy?useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=GMT%2B8
username=root
password=123456

JdbcUtils.class（工具类）

package com.king.lesson02.utils;

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


//工具类
public class JdbcUtils {

    private  static String driver=null;
    private  static String url=null;
    private  static String username=null;
    private  static String password=null;

    static {

        try{
            //获得类加载器.获得它的资源(返回了一个输入流)
            InputStream in = JdbcUtils.class.getClassLoader().getResourceAsStream("db.properties");
            Properties properties = new Properties();
            properties.load(in);

            driver=properties.getProperty("driver");
            url=properties.getProperty("url");
            username=properties.getProperty("username");
            password=properties.getProperty("password");

            //1.驱动只用加载一次
            Class.forName(driver);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //获取连接
    public  static Connection getConnection() throws SQLException {
            return DriverManager.getConnection(url, username, password);
    }

    //释放连接资源
    public static void release(Connection conn, Statement st, ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (st!=null){
            try {
                st.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}