开心一笑
爱神和月老
甲:“你知道西方国家闹离婚的为什么比中国的多吗?”
乙:“这还不简单,因为西方的爱神丘比特是个娃娃,而中国的是月下老人,经验当然丰富得多!”
提出问题
DriverManager类的简单学习???
解决问题
DriverManager在java.sql这个包里面,管理一组 JDBC 驱动程序的基本服务
[code]package com.evada.de; import java.sql.Connection; import java.sql.Driver; import java.sql.DriverManager; import java.util.Enumeration; /** * 用静态工厂方法管理一个唯一的可重用的连接 * Created by Ay on 2016/5/1. */ public class ConnUtils{ private ConnUtils(){} private static Connection con; //在静态代码块中创建与数据库的连接 static{ try{ //postgresql驱动名称 Class.forName("org.postgresql.Driver"); //数据库连接路径 String url = "jdbc:postgresql://127.0.0.1:5432/postgres"; //用户名和密码 con = DriverManager.getConnection(url, "postgres", "888888"); }catch(Exception e){ throw new RuntimeException(e.getMessage(),e); } } //使用一个静态方法-静态工厂方法,返回connection实例 public static Connection getCon(){ return con; } //main函数测试用 public static void main(String[] args) { //获取所有的数据库驱动 Enumeration<Driver> driverEnum = DriverManager.getDrivers(); //打印出所有驱动信息 while(driverEnum.hasMoreElements()){ System.out.println(driverEnum.nextElement()); } } }
运行结果:
[code]org.mariadb.jdbc.Driver@7cef4e59 com.alibaba.druid.proxy.DruidDriver@3ada9e37 com.alibaba.druid.mock.MockDriver@4ec6a292 org.postgresql.Driver@71c7db30
解释,因为我们的项目包里有如下图片的数据库驱动,所以会打印下面信息
这两者的区别:
DriverManager.registerDriver(new Driver()); Class.forName(“com.mysql.jdbc.Driver”);
org.postgresql.Driver类源码如下,可以看出postgresql是通过单例形式,new一个驱动Driver,也就是说在连接数据库是只new了一个Driver
[code]static { sharedTimer = new SharedTimer(logger); try { //注册 register(); } catch (SQLException var1) { throw new ExceptionInInitializerError(var1); } protocols = new String[]{"jdbc", "postgresql"}; } public static void register() throws SQLException { if(isRegistered()) { throw new IllegalStateException("Driver is already registered......); } else { Driver registeredDriver = new Driver(); DriverManager.registerDriver(registeredDriver); registeredDriver = registeredDriver; } }
再来看看DriverManager的源码,它会把Driver包装到DriverInfo中,
[code]// public static synchronized void registerDriver(java.sql.Driver driver, DriverAction da) throws SQLException { /* Register the driver if it has not already been added to our list */ if(driver != null) { //将驱动包装到DriverInfo中 registeredDrivers.addIfAbsent(new DriverInfo(driver, da)); } else { // This is for compatibility with the original DriverManager throw new NullPointerException(); } println("registerDriver: " + driver); }
Class.forName(“com.mysql.jdbc.Driver”);
结论:DriverManager.registerDriver(new Driver()); 多new一个Driver浪费;而Class.forName(“com.mysql.jdbc.Driver”); 单例形式,更推荐……
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