package com.sjx.tool;import java.io.FileInputStream;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;public class JDBCUtils {private static String driver;private static String url;private static String user;private static String password;static{try {//0读取配置文件Properties prop  = new Properties();InputStream is = new FileInputStream("src/db.properties");prop.load(is);is.close();driver = prop.getProperty("driver");url = prop.getProperty("url");user = prop.getProperty("user");password = prop.getProperty("password");//1 注册驱动
            Class.forName(driver);} catch (Exception e) {e.printStackTrace();}}//1 获得连接public static Connection getConnection(){Connection conn = null;try {//2 获得连接conn = DriverManager.getConnection(url, user, password);} catch (Exception e) {e.printStackTrace();throw new RuntimeException("创建连接失败!");}return conn;}//2 释放资源//1> 参数可能为空//2> 调用close方法要抛出异常,确保即使出现异常也能继续关闭//3>关闭顺序,需要从小到大public  static void  close(Connection conn , Statement st , ResultSet rs){try {if(rs!=null){rs.close();}} catch (SQLException e) {e.printStackTrace();}finally{try {if(st!=null){st.close();    }} catch (SQLException e) {// TODO Auto-generated catch block
                e.printStackTrace();}finally{try {if(conn!=null){conn.close();    }} catch (SQLException e) {// TODO Auto-generated catch block
                    e.printStackTrace();}}}}public static void main(String[] args) {System.out.println(getConnection());　　//本机安装的数据库能接受的连接数是极少的，所以少执行几次}
}