DriverManager.registerDriver(new Driver());与Class.forName(“com.mysql.jdbc.Driver”);的区别

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……


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