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
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,
// 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……