连接和关闭资源工具类

做一个工具类，里面封装了两个方法，一个用来获得连接，一个用来关闭资源

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
    }
}