JDBC基础

1.JDBC 2.JDBC连接 3.寻找properties配置文件 4.JDBC连接数据库（配置文件版 5.结果集回滚

JDBC是JAVA连接数据库的工具API

import java.sql.*;
public class Test{
	public static void main(String[] args)throws Exception{
		//1.注册驱动(造桥人
		Class.forName("com.mysql.cj.jdbc.Driver");
		//2.获取链接(造桥
		String url = "jdbc:mysql://127.0.0.1:3306/et2202?useSSL=false&serverTimezone=UTC";
		String user = "root";
		String pwd = "etoak";
		Connection con = DriverManager.getConnection(url,user,pwd);
		//3.创建Statement执行器，运行SQL语句(造车
		String sql = "select * from student where id > ?";
		PreparedStatement ps = con.prepareStatement(sql);
		ps.setInt(1,0);
		//4.得到数据集(装桶，拉回来
		ResultSet rs = ps.executeQuery();
		//5.处理数据集
		while(rs.next()){
			int id = rs.getInt("id");
			String name = rs.getString("name");
			String email = rs.getString("email");
			System.out.println(id+"t"+name+"t"+"t"+email);
		}
		//6.关闭资源
		rs.close();
		ps.close();
		con.close();
	}
}

1.包里面寻找

InputStream is = Test[项目名].class.getResourceAsStream("../../../db.properties");

2.包外面寻找

InputStream is = Test[项目名].getClassLoader().getResourceAsStream("db.properties");

1.db.properties文件

url = jdbc:mysql://127.0.0.1:3306/et2202?characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai&rewriteBatchedStatements=true&allowPublicKeyRetrieval=true
user = root
password = etoak
driver = com.mysql.cj.jdbc.Driver

2.Test.java文件

import java.io.*;
import java.sql.*;
import java.util.*;
public class Test{
	public static void main(String[] args)throws Exception{
		Connection con = getCon();
		String sql = "select * from student";
		PreparedStatement ps = con.prepareStatement(sql);
		ResultSet rs = ps.executeQuery();
		while(rs.next()){
			String name = rs.getString("name");
			int id = rs.getInt("id");
			String email = rs.getString("email");
			System.out.println(id+"t"+name+"t"+email);
		}
		rs.close();
		ps.close();
		con.close();
	}
	//读取.properties文件
	private static Properties getPro()throws Exception{
		Properties pro = new Properties();
		InputStream is = Test.class.getResourceAsStream("./db.properties");
		pro.load(is);
		return pro;
	}
	//获取链接
	private static Connection getCon()throws Exception{
		Properties pro = getPro();
		Class.forName(pro.getProperty("driver"));
		//第一种
		//Connection con = DriverManager.getConnection(pro.url,pro.user,pro.password);
		//第二种，properties文件中需要有user+password键，否则无法使用
		Connection con = DriverManager.getConnection(pro.getProperty("url"),pro);

		return con;
	}
}

//结果集回滚到第一条数据之前
rs.beforeFirst();
//结果集定位到第二条数据
rs.absolute(2);